Hurricane Isabel

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Matt-hurricanewatcher
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Hurricane Isabel

#1 Postby Matt-hurricanewatcher » Fri Jul 25, 2008 10:28 pm

I find it a little weird to have a 2003 archives without isabel thread.

ZCZC MIATCDAT3 ALL
TTAA00 KNHC DDHHMM
TROPICAL STORM ISABEL SPECIAL DISCUSSION NUMBER 1
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
9 AM EDT SAT SEP 06 2003

SATELLITE DATA INDICATE THAT THE TROPICAL WAVE IN THE FAR EASTERN
ATLANTIC HAS BECOME BETTER ORGANIZED AND IS NOW TROPICAL STORM
ISABEL. SINCE THE SHEAR IS LOW AHEAD OF THE TROPICAL CYCLONE A
GRADUAL STRENGTHENING IS INDICATED.

ISABEL IS MOVING WESTWARD AT 11 KNOTS. THIS GENERAL TRACK IS
EXPECTED TO CONTINUE DURING THE NEXT 2 TO 3 DAYS WITH A GRADUAL
TURN TO THE WEST-NORTHWEST AS THE WESTERN PORTION OF THE
SUBTROPICAL RIDGE WEAKENS.

A REGULAR ADVISORY WILL BE ISSUED AT 1500Z TODAY.

FORECASTER AVILA

FORECAST POSITIONS AND MAX WINDS

INITIAL 06/1300Z 14.0N 34.0W 35 KT
12HR VT 06/1800Z 14.0N 35.0W 40 KT
24HR VT 07/0600Z 14.0N 37.5W 45 KT
36HR VT 07/1800Z 14.5N 40.0W 55 KT
48HR VT 08/0600Z 15.0N 42.5W 65 KT
72HR VT 09/0600Z 15.5N 46.5W 65 KT
96HR VT 10/0600Z 16.5N 50.0W 65 KT
120HR VT 11/0600Z 17.5N 54.5W 65 KT


MIATCDAT3 ALL
TTAA00 KNHC DDHHMM
TROPICAL STORM ISABEL DISCUSSION NUMBER 2
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
11 AM EDT SAT SEP 06 2003

SATELLITE IMAGES SHOW THAT THE CLOUD PATTERN ASSOCIATED WITH ISABEL
IS GRADUALLY BECOMING BETTER ORGANIZED. IT APPEARS TO BE DEVELOPING
A CENTRAL DENSE OVERCAST AND HAS A WELL DEFINED CURVED BAND. THE
OUTFLOW IS FAIR IN ALL QUADRANTS BUT THE NORTHEAST. THE SHEAR IS
FORECAST TO REMAIN LOW OVER THE TROPICAL ATLANTIC AS INDICATED BY
GLOBAL AND SHIPS MODELS. IN ADDITION...SSTS ARE INCREASING ALONG
THE PATH OF ISABEL. THEREFORE...STRENGHTENING IS INDICATED AND
ISABEL MAY BECOME A HURRICANE IN THE NEXT 2 OR 3 DAYS.

MORE RECENT VISIBLE SATELLITE IMAGES INDICATE THAT THE CENTER
APPEARS TO BE A LITTLE TO THE SOUTH OF PREVIOUSLY INDICATED. BEST
ESTIMATE OF THE INITIAL MOTION IS 270 AT 12 KNOTS. BECAUSE THE
SUBTROPICAL RIDGE IS WELL ESTABLISHED TO THE NORTH OF ISABEL...A
WESTWARD MOTION IS EXPECTED TO CONTINUE. A GRADUAL TURN TO THE
WEST-NORTHWEST IS POSSIBLE IN ABOUT 4 TO 5 DAYS AS THE TROPICAL
CYCLONE APPROACHES A WEAKNESS OF THE RIDGE. THE OFFICIAL FORECAST
IS SIMILAR TO THE LATEST GFS.

FORECASTER AVILA

FORECAST POSITIONS AND MAX WINDS

INITIAL 06/1500Z 13.6N 34.5W 35 KT
12HR VT 07/0000Z 13.7N 36.4W 40 KT
24HR VT 07/1200Z 14.0N 39.0W 45 KT
36HR VT 08/0000Z 14.5N 41.5W 55 KT
48HR VT 08/1200Z 15.0N 44.0W 65 KT
72HR VT 09/1200Z 16.0N 48.0W 65 KT
96HR VT 10/1200Z 17.0N 51.9W 65 KT
120HR VT 11/1200Z 18.0N 56.5W 65 KT


ZCZC MIATCDAT3 ALL
TTAA00 KNHC DDHHMM
TROPICAL STORM ISABEL DISCUSSION NUMBER 3
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
5 PM EDT SAT SEP 06 2003

SATELLITE IMAGES DURING THE DAY INDICATE THAT ISABEL HAS CONTINUED
TO BECOME BETTER ORGANIZED. THE TROPICAL STORM HAS A LARGE ENVELOPE
DEFINED BY LOW CLOUDS ON SATELLITE...CONVECTIVE CURVED BANDS AND AN
EXPANDING CENTRAL DENSE OVERCAST. THE OUTFLOW CONTINUES TO BE
FAIRLY GOOD IN ALL QUADRANTS BUT THE NORTHEAST. SATELLITE INTENSITY
ESTIMATES AND AN EARLIER ADEOS SCATTEROMETER SUPPORT INCREASING THE
WINDS TO 45 KNOTS. THE OCEAN IS PLENTY WARM AHEAD OF ISABEL AS
INDICATED BY BUOYS AND THE SHEAR IS FORECAST TO REMAIN LOW.
THEREFORE...ISABEL IS FORECAST TO BECOME A HURRICANE.

A 24 TO 36 HOUR SATELLITE LOOP INDICATES THAT ISABEL HAS BEEN MOVING
SOUTH OF DUE WEST...OR PERHAPS IT WAS A REFORMATION UNDER THE
MID-LEVEL CIRCULATION. THE TROPICAL CYCLONE IS FORECAST TO MOVE
ABOUT 10 TO 12 KNOTS TOWARD THE WEST STEERED BY A RATHER STRONG
SUBTROPICAL RIDGE TO THE NORTH. HOWEVER...IN 3 TO 5 DAYS...THE
RIDGE IS EXPECTED TO ERODE AND ISABEL COULD BEGIN TO MOVE TO THE
WEST-NORTHWEST. THE OFFICIAL FORECAST IS SIMILAR TO THE GLOBAL
MODEL CONSENSUS...GUNA...BUT A LITTLE BIT BIASED TOWARD THE GFS.
THE LATTER IS THE ONLY MODEL THAT BRINGS THE TROPICAL CYCLONE VERY
CLOSE TO THE LEEWARD ISLANDS BEYOND 5 DAYS.

FORECASTER AVILA

FORECAST POSITIONS AND MAX WINDS

INITIAL 06/2100Z 13.4N 35.4W 45 KT
12HR VT 07/0600Z 13.4N 36.8W 50 KT
24HR VT 07/1800Z 13.5N 38.5W 60 KT
36HR VT 08/0600Z 14.5N 40.5W 65 KT
48HR VT 08/1800Z 15.5N 43.0W 70 KT
72HR VT 09/1800Z 17.0N 48.5W 75 KT
96HR VT 10/1800Z 18.0N 53.5W 75 KT
120HR VT 11/1800Z 18.5N 58.0W 75 KT


ZCZC MIATCDAT3 ALL
TTAA00 KNHC DDHHMM
TROPICAL STORM ISABEL DISCUSSION NUMBER 4
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
11 PM EDT SAT SEP 06 2003

SATELLITE IMAGERY DURING THE EVENING SHOWS THAT ISABEL HAS A
WELL-DEFINED CURVED CONVECTIVE BAND WITH TOPS COLDER THAN -80C.
THE CIRRUS OUTFLOW IS EXCELLENT OVER THE SOUTH SEMICIRCLE AND FAIR
TO GOOD ELSEWHERE. SATELLITE INTENSITY ESTIMATES ARE 55 KT FROM
TAFB AND SAB...AND 45 KT FROM AFWA. THE INITIAL INTENSITY IS
RAISED TO 50 KT FOR THIS ADVISORY.

THE INITIAL MOTION IS 270/09. WATER VAPOR IMAGERY INDICATES THAT
ISABEL IS SOUTH OF A MID/UPPER-LEVEL RIDGE...WITH AN UPPER-LEVEL
LOW CENTERED NEAR 26N46W. LARGE-SCALE MODELS SUGGEST THAT THIS LOW
WILL CREATE ENOUGH WEAKNESS IN THE RIDGE TO ALLOW ISABEL TO
GRADUALLY TURN TO A WEST-NORTHWESTWARD COURSE DURING THE NEXT 24-48
HR...AND CONTINUE THAT GENERAL MOTION THROUGH DAY 5. NHC TRACK
GUIDANCE AGREES WITH THIS SCENARIO. SINCE SOME MODELS SHOWED
SOMEWHAT OF A NORTHWARD BIAS WHEN FABIAN WAS IN THIS AREA...THE
OFFICIAL FORECAST WILL LEAN TOWARD THE SOUTH SIDE OF THE GUIDANCE.
IT IS ALSO NUDGED JUST A LITTLE SOUTH OF THE PREVIOUS TRACK.

ISABEL SEEMS TO HAVE ALL THE INGREDIENTS TO STRENGTHEN
SIGNIFICANTLY...A LARGE CYCLONIC ENVELOPE...GOOD CONVECTIVE
STRUCTURE...COLD CLOUD TOPS...AND FAVORABLE OUTFLOW AND VERTICAL
SHEAR. THE SHIPS MODEL TAKES THE STORM TO 80 KT IN 60 HR AND THEN
STOPS INTENSIFICATION FOR REASONS NOT READILY APPARENT. THE GFDL
MAKES ISABEL A 90 KT HURRICANE IN 120 HR. THE INTENSITY FORECAST
WILL SHOW THE INTENSITY LEVELING OFF AT 80 KT IN AGREEMENT WITH THE
SHIPS MODEL. HOWEVER...IT WOULD NOT BE A SURPRISE TO SEE ISABEL
STRENGTHEN FASTER AND MORE THAN CURRENTLY FORECAST.

FORECASTER BEVEN

FORECAST POSITIONS AND MAX WINDS

INITIAL 07/0300Z 13.4N 36.1W 50 KT
12HR VT 07/1200Z 13.4N 37.4W 60 KT
24HR VT 08/0000Z 13.8N 39.4W 65 KT
36HR VT 08/1200Z 14.7N 41.8W 70 KT
48HR VT 09/0000Z 15.6N 44.4W 75 KT
72HR VT 10/0000Z 17.0N 49.4W 80 KT
96HR VT 11/0000Z 18.0N 54.5W 80 KT
120HR VT 12/0000Z 18.5N 59.0W 80 KT


NNNN

ZCZC MIATCDAT3 ALL
TTAA00 KNHC DDHHMM
TROPICAL STORM ISABEL DISCUSSION NUMBER 5
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
5 AM EDT SUN SEP 07 2003

OVERNIGHT SATELLITE IMAGERY SHOWS THAT ISABEL CONTINUES TO EXHIBIT A
WELL-DEFINED CURVED CONVECTIVE BAND...AND THE LAST FEW IMAGES
SUGGEST THAT THE CONVECTION HAS BEGUN TO WRAP CLOSER TO THE CENTER.
SATELLITE INTENSITY ESTIMATES ARE A CONSENSUS 55 KT FROM
TAFB...SAB...AND AFWA. THEREFORE...THE INITIAL INTENSITY IS RAISED
TO 55 KT FOR THIS ADVISORY. GLOBAL MODELS SUGGEST THAT A MID/UPPER
LEVEL RIDGE WILL REMAIN NORTH OF THE CYCLONE THROUGH THE FORECAST
PERIOD...PROVIDING FAVORABLE CONDITIONS FOR STRENGTHENING. THE
SHIPS MODEL TAKES ISABEL TO 85 KT IN 72 HOURS...AND THE GFDL BRINGS
THE INTENSITY UP TO 95 KT IN 48 HOURS. THE INTENSITY FORECAST WILL
BE RATHER CONSERVATIVE AND INDICATE GRADUAL STRENGTHENING OVER THE
NEXT 2-3 DAYS...WITH THE INTENSITY LEVELING OFF AT 85 KT BY 72
HOURS WHICH IS IN GENERAL AGREEMENT WITH SHIPS.

THE INITIAL MOTION IS 275/09...SLIGHTLY NORTH OF THE PREVIOUS
ADVISORY. THE SYNOPTIC PATTERN REMAINS BASICALLY UNCHANGED FROM
THE PREVIOUS FORECAST...WITH ISABEL BEING STEERED BY A MID/UPPER
LEVEL RIDGE TO THE NORTH. WATER VAPOR IMAGERY INDICATES AN
UPPER-LEVEL TROUGH ABOUT 900 NM NORTHWEST OF THE TROPICAL CYCLONE.
LARGE-SCALE GLOBAL MODELS SUGGEST THAT THIS TROUGH WILL CREATE JUST
ENOUGH OF A WEAKNESS IN THE RIDGE TO ALLOW FOR A MORE
WEST-NORTHWEST MOTION BEYOND 12 HOURS...AND CONTINUE THAT MOTION
THROUGH DAY 5. NHC TRACK GUIDANCE BASICALLY FOLLOWS THIS
SCENARIO...WITH THE FORECAST TRACK ADJUSTED A TAD TO THE NORTH OF
THE PREVIOUS TRACK AND REMAINING ON THE SOUTH SIDE OF THE GUIDANCE.

FORECASTER MOLLEDA/LAWRENCE

FORECAST POSITIONS AND MAX WINDS

INITIAL 07/0900Z 13.7N 37.1W 55 KT
12HR VT 07/1800Z 13.8N 38.5W 60 KT
24HR VT 08/0600Z 14.8N 40.9W 65 KT
36HR VT 08/1800Z 15.6N 43.2W 70 KT
48HR VT 09/0600Z 16.5N 45.3W 75 KT
72HR VT 10/0600Z 18.0N 50.0W 85 KT
96HR VT 11/0600Z 18.5N 55.5W 85 KT
120HR VT 12/0600Z 19.0N 60.0W 85 KT

ZCZC MIATCDAT3 ALL
TTAA00 KNHC DDHHMM
HURRICANE ISABEL DISCUSSION NUMBER 6
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
11 AM EDT SUN SEP 07 2003

SATELLITE IMAGERY THIS MORNING INDICATES THAT ISABEL HAS DEVELOPED A
VERY LARGE RAGGED EYE. SATELLITE INTENSITY ESTIMATES ARE 65 KT FROM
TAFB AND SAB...AND 77 KT FROM AFWA...SO THE INITIAL INTENSITY IS
SET AT 65 KT. THE UPPER-LEVEL OUTFLOW PATTERN IS NEARLY CIRCULAR
AND APPEARS TO BE UNRESTRICTED AND EXPANDING.

THE INITIAL MOTION IS 295/09...BASED ON ABOUT A 9 HOUR MOTION
BETWEEN SUCCESSIVE MICROWAVE POSITIONS. THE EYE FEATURE IS RAGGED
AND NOT REALLY A TRUE EMBEDDED EYE. CONVENTIONAL WATER VAPOR AND
SSMI VAPOR SATELLITE IMAGERY INDICATE DRY AIR HAS BEEN WRAPPING
INTO THE CENTER FROM THE SOUTHEAST THROUGH NORTHEAST...WHICH HAS
ACTUALLY ERODED THE CONVECTION ON THE NORTH SIDE. FOR THIS REASON
...THE INITIAL POSITION WAS PLACED NEAR THE SOUTHERN EDGE OF THE
'EYE' AND CLOSER TO THE DEEPEST CONVECTION. EVEN WITH THAT...THE
INITIAL POSITION IS STILL MORE THAN 40 NMI NORTH OF THE PREVIOUS
ADVISORY POSITION. THE GLOBAL MODELS ARE IN FAIRLY GOOD AGREEMENT
AND THERE IS GOOD CONVERGENCE ON A WEST-NORTHWESTWARD TRACK THROUGH
48-72 HOURS...WITH A MORE WESTWARD MOTION AFTER THAT. THIS IS
CONSISTENT WITH THE DEVELOPING SYNOPTIC PATTERN...WHICH INDICATES
THAT THE SUBTROPICAL RIDGE ALONG 32N LATITUDE SHOULD GRADUALLY
SHIFT WESTWARD AND PERHAPS EVEN CLOSE OFF A 500 MB HEIGHT CENTER A
COUPLE HUNDRED MILES SOUTHEAST OF BERMUDA. THE OFFICIAL TRACK IS
SIMILAR TO BUT TO THE RIGHT OF THE PREVIOUS TRACK...MAINLY DUE TO
THE MORE NORTHERLY INITIAL POSITION.

AT LEAST STEADY STRENGTHENING SHOULD OCCUR SINCE ISABEL NOW HAS AN
EYE FEATURE...IS OVER 82F WATER WITH WARMER SSTS AHEAD...AND HAS AN
IMPRESSIVE OUTFLOW PATTERN. BOTH THE SHIPS AND GFDL INTENSITY
MODELS BRING ISABEL UP TO 96 KT IN 42-60 HOURS...SO THIS TREND WAS
CLOSELY FOLLOWED. THE INTENSITY WAS LEVELED OFF AFTER 48 HOURS
SINCE ISABEL IS FORECAST TO BEGIN CROSSING A POSSIBLE COLD WAKE
LEFT BEHIND BY HURRICANE FABIAN LAST WEEK.

FORECASTER STEWART

FORECAST POSITIONS AND MAX WINDS

INITIAL 07/1500Z 14.5N 37.7W 65 KT
12HR VT 08/0000Z 15.1N 39.2W 75 KT
24HR VT 08/1200Z 15.8N 41.3W 85 KT
36HR VT 09/0000Z 16.6N 43.8W 95 KT
48HR VT 09/1200Z 17.3N 46.3W 100 KT
72HR VT 10/1200Z 18.5N 51.0W 100 KT
96HR VT 11/1200Z 19.0N 55.5W 100 KT
120HR VT 12/1200Z 19.5N 60.0W 100 KT


Becomes a hurricane.


ZCZC MIATCDAT3 ALL
TTAA00 KNHC DDHHMM
HURRICANE ISABEL DISCUSSION NUMBER 7
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
5 PM EDT SUN SEP 07 2003

THE ALLEGED EYE OF ISABEL PASSED OVER BUOY 13008 LOCATED AT 15N 38W
BETWEEN 14-15Z. THE BUOY REPORTED 37 KT AND 24 KT NORTHEAST WINDS
...TO THE SOUTH OF ALL THE SATELLITE CENTER POSITIONS. THESE WIND
REPORTS SUGGEST THAT THE ACTUAL CENTER IS FARTHER SOUTH NEAR THE
SOUTHERN PORTION OF THE EYE FEATURE...AS MENTIONED IN THE PREVIOUS
DISCUSSION. DURING THE PAST 6 HOURS...THE EYE FEATURE...OVERALL
CONVECTIVE PATTERN...AND OUTFLOW PATTERN HAVE CONTINUED TO IMPROVE.
THE INITIAL INTENSITY OF 70 KT IS BASED ON SATELLITE INTENSITY
ESTIMATES OF 65 KT FROM TAFB AND SAB...AND 77 KT FROM AFWA.

THE INITIAL MOTION ESTIMATE IS 295/13. THE INITIAL POSITION REMAINS
ABOUT 24 NMI SOUTH OF THE SATELLITE POSITIONS. THE 12Z GLOBAL
MODELS ARE IN EVEN BETTER AGREEMENT NOW ON KEEPING AT LEAST A
MODERATE SUBTROPICAL RIDGE NORTH OF ISABEL ALONG 32N LATITUDE
THROUGHOUT THE FORECAST PERIOD...AND EVEN BUILD IT WESTWARD ACROSS
THE BAHAMAS AND FLORIDA. THIS SHOULD KEEP ISABEL MOVING
WEST-NORTHWESTWARD THROUGH 48-72 HOURS...WITH A GRADUAL WESTWARD
MOTION DEVELOPING AFTER THAT. THE PREVIOUS FORECAST TRACK WAS ONLY
SHIFTED SLIGHTLY NORTHWARD AND SLOWED A LITTLE AFTER 72 HOURS...
WHICH IS CONSISTENT WITH THE GLOBAL MODEL CONSENSUS.

ISABEL CURRENTLY HAS A VERY IMPRESSIVE OUTFLOW PATTERN AND...
UNFORTUNATELY...THE GLOBAL MODELS ARE FORECASTING IT TO BECOME EVEN
BETTER. BY 36-48 HOURS... ALL OF THE GLOBAL MODELS EXCEPT THE UKMET
ARE FORECASTING MORE THAN 50 KT OF OUTFLOW ON THE WEST SIDE OF
ISABEL BEING DRAWN INTO AN UPPER-LEVEL LOW LOCATED JUST NORTHEAST
OF THE LEEWARD ISLANDS. A PATTERN LIKE THAT CAN OFTENTIMES LEAD TO
RAPID OR EXPLOSIVE DEEPENING. THE SHIPS INTENSITY MODEL BRINGS
ISABEL UP TO 97 KT IN 60 HOURS...BUT THE OFFICIAL FORECAST IS A
LITTLE HIGHER SINCE SHIPS WAS LOW/SLOW WITH THE INTENSIFICATION OF
FABIAN. THE INTENSITY WAS LEVELED OFF AFTER 48 HOURS SINCE ISABEL
MAY CROSS A POSSIBLE COLD WAKE LEFT BEHIND BY HURRICANE FABIAN.

FORECASTER STEWART

FORECAST POSITIONS AND MAX WINDS

INITIAL 07/2100Z 15.2N 39.1W 70 KT
12HR VT 08/0600Z 15.8N 40.5W 75 KT
24HR VT 08/1800Z 16.5N 42.8W 85 KT
36HR VT 09/0600Z 17.2N 45.2W 95 KT
48HR VT 09/1800Z 18.0N 47.7W 100 KT
72HR VT 10/1800Z 19.0N 52.0W 100 KT
96HR VT 11/1800Z 19.5N 55.5W 100 KT
120HR VT 12/1800Z 19.5N 60.0W 100 KT




ZCZC MIATCDAT3 ALL
TTAA00 KNHC DDHHMM
HURRICANE ISABEL DISCUSSION NUMBER 8
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
11 PM EDT SUN SEP 07 2003

ISABEL CONTINUES TO GET BETTER ORGANIZED AND HAS IMPRESSIVE COLD
CLOUD TOPS SURROUNDING THE 35 NMI DIAMETER EYE. THE INITIAL
INTENSITY OF 80 KT IS BASED ON SATELLITE INTENSITY ESTIMATES OF 77
KT FROM TAFB AND SAB...AND 90 KT FROM AFWA.

THE INITIAL MOTION ESTIMATE IS 285/13. ISABEL IS MOVING IN THIS
DIRECTION IN RESPONSE TO A SUBTROPICAL RIDGE TO THE NORTH. THE
GLOBAL MODELS ARE ALL IN AGREEMENT THAT THE RIDGE WILL REMAIN
THROUGHOUT THE FORECAST PERIOD AND ISABEL SHOULD CONTINUE TO MOVE
IN A WEST-NORTHWEST TO WEST MOTION FOR THE NEXT FIVE DAYS WITH THE
SYSTEM ENDING UP JUST TO THE NORTHEAST OF THE LEEWARD ISLANDS ON
DAY FIVE. THE OFFICIAL FORECAST REFLECTS THIS AND IS ESSENTIALLY AN
UPDATE OF THE PREVIOUS FORECAST.

THE SHIPS MODEL SEEMS TO BE HANDLING THE INTENSIFICATION OF ISABEL
VERY WELL SO THE INTENSITY FORECAST BASICALLY FOLLOWS THE SHIPS
GUIDANCE.

FORECASTER JARVINEN

FORECAST POSITIONS AND MAX WINDS

INITIAL 08/0300Z 16.1N 40.2W 80 KT
12HR VT 08/1200Z 16.8N 42.0W 85 KT
24HR VT 09/0000Z 17.7N 44.4W 90 KT
36HR VT 09/1200Z 18.5N 46.9W 95 KT
48HR VT 10/0000Z 19.2N 49.3W 100 KT
72HR VT 11/0000Z 19.7N 53.2W 100 KT
96HR VT 12/0000Z 20.2N 56.7W 100 KT
120HR VT 13/0000Z 20.5N 60.0W 100 KT


NNNN


ZCZC MIATCDAT3 ALL
TTAA00 KNHC DDHHMM
HURRICANE ISABEL DISCUSSION NUMBER 9
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
5 AM EDT MON SEP 08 2003

ISABEL CONTINUES TO GET BETTER ORGANIZED AND HAS IMPRESSIVE COLD
CLOUD TOPS SURROUNDING THE EYE WHICH HAS DECREASED IN DIAMETER SINCE
THE LAST ADVISORY. THE INITIAL INTENSITY IS NOW 90 KT AND IS BASED
ON SATELLITE INTENSITY ESTIMATES OF 102 KTS FROM TAFB AND 90 KTS
FROM SAB AND AIR FORCE GLOBAL. IN FACT...ISABEL MAY BE STRONGER BUT
I WANT TO SEE IF IT CAN MAINTAIN THESE SATELLITES ESTIMATES FOR AT
LEAST ANOTHER CYCLE BEFORE I GO ABOVE 90 KTS

THE INITIAL MOTION ESTIMATE IS 300/14. ISABEL IS MOVING IN THIS
DIRECTION IN RESPONSE TO A SUBTROPICAL RIDGE TO THE NORTH. BUT...
WATER VAPOR IMAGERY ALSO SHOWS AN UPPER COLD LOW THAT IS DEVELOPING
TO THE WEST OF ISABEL. THE SOUTHERLY AND SOUTHWESTERLY FLOW ON THE
EAST SIDE OF THIS COLD LOW MAY BE ADDING A NORTHERLY COMPONENT TO
THE MOTION. HOWEVER...THE GLOBAL MODELS EVENTUALLY MOVE THIS
SYSTEM TOWARD THE WEST AND WEAKEN IT. THE GLOBAL MODELS ARE ALL IN
AGREEMENT THAT THE RIDGE WILL REMAIN THROUGHOUT THE FORECAST PERIOD
AND ISABEL SHOULD CONTINUE TO MOVE IN A WEST-NORTHWEST TO WEST
MOTION FOR THE NEXT FIVE DAYS WITH THE SYSTEM ENDING UP JUST TO THE
NORTHEAST OF THE LEEWARD ISLANDS ON DAY FIVE. THE OFFICIAL FORECAST
REFLECTS THIS AND IS ESSENTIALLY AN UPDATE OF THE PREVIOUS
FORECAST.

THE SHIPS MODEL INTENSIFIES ISABEL TO 115 KTS IN 48 HOURS AND THE
OFFICIAL INTENSITY FORECAST REFLECTS THIS. HOWEVER...THE SYSTEM
MAY BE IN A RAPID DEEPENING MODE AND MAY GET STRONGER SOONER.

FORECASTER JARVINEN

FORECAST POSITIONS AND MAX WINDS

INITIAL 08/0900Z 16.9N 41.4W 90 KT
12HR VT 08/1800Z 17.9N 43.3W 100 KT
24HR VT 09/0600Z 18.8N 45.7W 105 KT
36HR VT 09/1800Z 19.4N 48.0W 110 KT
48HR VT 10/0600Z 19.8N 50.3W 115 KT
72HR VT 11/0600Z 19.9N 54.4W 115 KT
96HR VT 12/0600Z 20.2N 58.0W 115 KT
120HR VT 13/0600Z 20.6N 60.7W 115 KT


NNNN

MIATCDAT3 ALL
TTAA00 KNHC DDHHMM
HURRICANE ISABEL DISCUSSION NUMBER 10
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
11 AM EDT MON SEP 08 2003

ISABEL HAS CONTINUED TO RAPIDLY INTENSIFY. THE INITIAL INTENSITY IS
INCREASED TO 100 KT BASED ON SATELLITE INTENSITY ESTIMATES OF 115
KT FROM TAFB AND AFWA...102 KT FROM SAB...AND 102 KT/T5.5 3-HOUR
OBJECTIVE DVORAK INTENSITY ESTIMATES. THE 100 KT INITIAL INTENSITY
IS ALSO CONSISTENT WITH THE LATEST AMSU INTENSITY ESTIMATES OF 100
KT AND 960 MB. OUTFLOW REMAINS QUITE IMPRESSIVE AND CONTINUES TO
IMPROVE AND THE EYE DIAMETER HAS DECREASED DOWN TO 25 NMI.

THE INITIAL MOTION ESTIMATE IS 290/12. IS APPEARS THAT ISABEL MAY BE
MAKING THE MORE WESTWARD TURN THAT THE GLOBAL MODELS HAVE BEEN
INDICATING. THE NHC MODEL GUIDANCE IS EVEN MORE TIGHTLY PACKED AND
IN GOOD AGREEMENT ON ISABEL MOVING WEST-NORTHWESTWARD FOR THE NEXT
36 HOURS...AND THEN TURNING MORE WESTWARD AFTER THAT. THIS IS QUITE
REASONABLE GIVEN THE STRENGTH AND EAST-WEST ORIENTATION OF THE
SUBTROPICAL RIDGE LOCATED ALONG 32N LATITUDE. A DISCONCERTING PART
OF THE MODEL GUIDANCE IS THE GFS AND NOGAPS MODELS CONTINUING TO
INSIST THAT ISABEL WILL MAKE A DIP SOUTH-OF-WEST AFTER 72 HOURS.
THEY BRING ISABEL DANGEROUSLY CLOSE TO THE NORTHERN LEEWARD ISLANDS
BY 120 HOURS. THE GFS AND NOGAPS HAD A LEFT OF TRACK BIAS WITH
FABIAN LAST WEEK...SO I PREFER TO WAIT ANOTHER 24 HOURS OR SO TO
SEE IF THIS SAME BIAS DEVELOPS. HOWEVER...THIS SCENARIO CAN NOT BE
COMPLETELY RULED OUT GIVEN THE DEEP MID-/UPPER-LEVEL TROUGH
NORTHWEST OF AFRICA THAT HAS BEEN DIGGING SOUTHWESTWARD. THAT COULD
CREATE ENOUGH LOW-LEVEL RIDGING FROM THE NORTHEAST TO NUDGE ISABEL
A LITTLE SOUTH OF DUE WEST...SIMILAR TO THE GFS-NOGAPS SCENARIO.

ISABEL IS ABOUT 18-24 HOURS INTO A RAPID INTENSIFICATION CYCLE...SO
THIS TREND IS FORECAST TO CONTINUE FOR ANOTHER 12 HOURS OR SO.
AFTER REACHING CATEGORY 4 INTENSITY...INNER-CORE CONVECTION AND
EYEWALL DYNAMICS WILL DICTATE ANY INTENSITY CHANGES. HOWEVER...THE
INTENSITY FORECAST COULD EASILY BE TOO LOW GIVEN THE CURRENT AND
FORECAST OUTFLOW PATTERN THAT WILL EVOLVE OVER THE NEXT 48 HOURS.

FORECASTER STEWART

FORECAST POSITIONS AND MAX WINDS

INITIAL 08/1500Z 17.2N 42.6W 100 KT
12HR VT 09/0000Z 17.9N 44.4W 115 KT
24HR VT 09/1200Z 18.6N 46.8W 120 KT
36HR VT 10/0000Z 19.2N 49.1W 120 KT
48HR VT 10/1200Z 19.4N 51.1W 120 KT
72HR VT 11/1200Z 19.5N 55.0W 120 KT
96HR VT 12/1200Z 19.5N 58.5W 120 KT
120HR VT 13/1200Z 20.0N 62.5W 120 KT


NNNN


ZCZC MIATCDAT3 ALL
TTAA00 KNHC DDHHMM
HURRICANE ISABEL DISCUSSION NUMBER 11
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
5 PM EDT MON SEP 08 2003

ISABEL HAS CONTINUED ITS RAPID INTENSIFICATION TREND. THE INITIAL
INTENSITY IS INCREASED TO 110 KT BASED ON SATELLITE INTENSITY
ESTIMATES OF 115 KT FROM TAFB AND AFWA...102 KT FROM SAB...AND 113
KT/T5.9 3-HOUR OBJECTIVE DVORAK INTENSITY ESTIMATES. THE OUTFLOW
REMAINS VERY IMPRESSIVE AND THE OVERALL CONVECTIVE PATTERN HAS ALSO
CONTINUED TO IMPROVE.

THE INITIAL MOTION ESTIMATE IS 295/12. THERE HAS BEEN SOME WOBBLING
ALONG THE TRACK THE PAST 6 HOURS...WHICH IS TYPICAL OF INTENSE
HURRICANES. THE NHC MODEL GUIDANCE REMAINS IN GOOD AGREEMENT ON
ISABEL MOVING WEST-NORTHWESTWARD FOR THE NEXT 36 HOURS OR SO...AND
THEN TURNING MORE WESTWARD AFTER THAT. HOWEVER...THE GFS AND NOGAPS
MODELS MAINTAIN A WEST-SOUTHWESTWARD MOTION AFTER 48-72 HOURS. THE
REASON FOR THIS MORE SOUTHERLY TRACK IS NOT APPARENT IN THE MODEL
FIELDS...SO I AM CONTINUING TO PLACE LESS WEIGHT ON THAT SCENARIO
AT THIS TIME BASED ON THOSE MODELS HAVING A PREVIOUS LEFT-BIAS WITH
FABIAN. THE OFFICIAL FORECAST TRACK IS NUDGED SLIGHTLY NORTH OF THE
PREVIOUS TRACK THROUGH 36 HOURS...AND THEN COMES BACK ON TRACK
AFTER THAT. THIS IS CONSISTENT WITH THE GLOBAL MODEL CONSENSUS.

ISABEL IS 24 HOURS INTO A RAPID INTENSIFICATION CYCLE...BUT RARELY
DUE SUCH TRENDS OCCUR FOR MORE THAN 30-36 HOURS. THEREFORE...THE
CURRENT INTENSIFICATION TREND IS LEVELED OFF AFTER ABOUT 12 HOURS
OR SO. HOWEVER...UPPER-LEVEL CONDITIONS ARE FORECAST TO REMAIN
QUITE FAVORABLE THROUGHOUT THE FORECAST PERIOD...SO ISABEL COULD
STILL REACH CATEGORY 4 INTENSITY DURING THE NEXT 12 HOURS OR SO.
AFTER THAT...INNER-CORE CONVECTION AND EYEWALL DYNAMICS WILL
DICTATE ANY FURTHER INTENSITY CHANGES. HOWEVER...THE INTENSITY
FORECAST COULD EASILY BE TOO LOW GIVEN THAT THE OUTFLOW PATTERN IS
EXPECTED TO CONTINUE TO IMPROVE...THE VERTICAL SHEAR IS FORECAST TO
REMAIN LESS THAN 10 KT...AND ISABEL WILL BE MOVING OVER 28C AND
WARMER SSTS.

FORECASTER STEWART

FORECAST POSITIONS AND MAX WINDS

INITIAL 08/2100Z 17.9N 43.7W 110 KT
12HR VT 09/0600Z 18.6N 45.6W 120 KT
24HR VT 09/1800Z 19.2N 47.9W 125 KT
36HR VT 10/0600Z 19.5N 50.0W 125 KT
48HR VT 10/1800Z 19.5N 52.0W 125 KT
72HR VT 11/1800Z 19.5N 55.5W 125 KT
96HR VT 12/1800Z 19.5N 59.0W 125 KT
120HR VT 13/1800Z 20.0N 63.0W 125 KT

ZCZC MIATCDAT3 ALL
TTAA00 KNHC DDHHMM
HURRICANE ISABEL DISCUSSION NUMBER 12
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
11 PM EDT MON SEP 08 2003

DVORAK INTENSITY CLASSIFICATIONS FROM TAFB AND SAB WERE T6.0 OR 115
KT...AND THAT WILL BE THE ADVISORY INTENSITY. ISABEL HAS AN
IMPRESSIVE OUTFLOW PATTERN ALTHOUGH IT IS BEING SQUEEZED A LITTLE
BIT IN THE SOUTHWEST QUADRANT BY THE UPPER-LEVEL LOW TO ITS WEST.

THE INITIAL MOTION ESTIMATE IS 300/11. THERE IS A SPLIT IN THE
MODEL GUIDANCE THAT HAS SOME BEARING ON THE POTENTIAL THREAT TO THE
NORTHERN LEEWARD ISLANDS. WHILE THE CANADIAN AND UKMET MODELS BEND
THE TRACK ONLY SLIGHTLY TO THE LEFT FROM 24-72 HOURS...THE GFS AND
NOGAPS TURN THE TRACK HARDER...TO THE WEST-SOUTHWEST OR EVEN
SOUTHWEST...WHICH BRINGS THE CENTER UNCOMFORTABLY CLOSE TO THESE
ISLANDS. ONE DIFFERENCE IN THESE MODEL SOLUTIONS IS HOW STRONGLY
ISABEL INTERACTS WITH THE MID TO UPPER-LEVEL LOW CURRENTLY
APPROACHING THE HURRICANE FROM THE NORTHEAST...AS WELL AS THE
MID-LEVEL VORTEX ASSOCIATED WITH TROPICAL DEPRESSION FOURTEEN. IN
THE UKMET AND CANADIAN MODELS THERE IS NO APPRECIABLE
INTERACTION...WHILE IN THE GFS AND NOGAPS THE LOW IS CLOSE ENOUGH
TO DRAG ISABEL SOUTHWARD. IN PART BECAUSE OF THE IMPRESSIVE
ANTICYCLONIC OUTFLOW IN THE NORTHEAST QUADRANT OF ISABEL...AND THE
CURRENT DISARRAY OF TD FOURTEEN...MY FEELING IS THAT THE
INTERACTION IS BEING OVERDONE BY THE GFS AND NOGAPS. THE OFFICIAL
FORECAST IS VERY CLOSE TO THE GLOBAL MODEL CONSENSUS AND GFDL
SOLUTIONS...AND SLIGHTLY TO THE RIGHT OF THE PREVIOUS FORECAST.

I HAVE BACKED OFF A BIT FROM THE INTENSITY FORECAST OF THE PREVIOUS
ADVISORY. SST ANALYSES SHOW THAT ISABEL WILL BE PASSING OVER THE
COOL WAKE OF FABIAN IN ABOUT 36 HOURS...AND THERE COULD BE SOME
RESTRICTION OF THE OUTFLOW BY THE UPPER LOW APPROACHING FROM THE
NORTHEAST...EVEN IF THAT LOW DOES NOT COME CLOSE ENOUGH TO
APPRECIABLY AFFECT THE TRACK. IT IS ALSO QUITE RARE FOR STORMS TO
MAINTAIN MAJOR HURRICANE STATUS FOR FIVE DAYS. EVEN WITH THIS
ADJUSTMENT...THE OFFICIAL FORECAST REMAINS ABOVE THE GFDL AND SHIPS
INTENSITY GUIDANCE.

FORECASTER FRANKLIN

FORECAST POSITIONS AND MAX WINDS

INITIAL 09/0300Z 18.5N 44.5W 115 KT
12HR VT 09/1200Z 19.2N 46.2W 120 KT
24HR VT 10/0000Z 19.9N 48.5W 125 KT
36HR VT 10/1200Z 20.0N 50.6W 120 KT
48HR VT 11/0000Z 20.0N 52.5W 115 KT
72HR VT 12/0000Z 20.0N 56.0W 110 KT
96HR VT 13/0000Z 20.0N 59.5W 110 KT
120HR VT 14/0000Z 21.0N 63.0W 110 KT
Last edited by Matt-hurricanewatcher on Fri Jul 25, 2008 10:52 pm, edited 2 times in total.
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Re: Hurricane Isabel

#2 Postby Matt-hurricanewatcher » Fri Jul 25, 2008 10:30 pm

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Track of hurricane Isabel. Cat5!
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Re: Hurricane Isabel

#4 Postby Sciencerocks » Sat May 20, 2023 6:31 pm

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Re: Hurricane Isabel

#5 Postby Sciencerocks » Sat May 20, 2023 6:38 pm

TTAA00 KNHC DDHHMM
TROPICAL STORM ISABEL SPECIAL DISCUSSION NUMBER 1
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
9 AM EDT SAT SEP 06 2003

SATELLITE DATA INDICATE THAT THE TROPICAL WAVE IN THE FAR EASTERN
ATLANTIC HAS BECOME BETTER ORGANIZED AND IS NOW TROPICAL STORM
ISABEL. SINCE THE SHEAR IS LOW AHEAD OF THE TROPICAL CYCLONE A
GRADUAL STRENGTHENING IS INDICATED.

ISABEL IS MOVING WESTWARD AT 11 KNOTS. THIS GENERAL TRACK IS
EXPECTED TO CONTINUE DURING THE NEXT 2 TO 3 DAYS WITH A GRADUAL
TURN TO THE WEST-NORTHWEST AS THE WESTERN PORTION OF THE
SUBTROPICAL RIDGE WEAKENS.

A REGULAR ADVISORY WILL BE ISSUED AT 1500Z TODAY.

FORECASTER AVILA

FORECAST POSITIONS AND MAX WINDS

INITIAL 06/1300Z 14.0N 34.0W 35 KT
12HR VT 06/1800Z 14.0N 35.0W 40 KT
24HR VT 07/0600Z 14.0N 37.5W 45 KT
36HR VT 07/1800Z 14.5N 40.0W 55 KT
48HR VT 08/0600Z 15.0N 42.5W 65 KT
72HR VT 09/0600Z 15.5N 46.5W 65 KT
96HR VT 10/0600Z 16.5N 50.0W 65 KT
120HR VT 11/0600Z 17.5N 54.5W 65 KT

Image

ZCZC MIATCDAT3 ALL
TTAA00 KNHC DDHHMM
TROPICAL STORM ISABEL DISCUSSION NUMBER 2
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
11 AM EDT SAT SEP 06 2003

SATELLITE IMAGES SHOW THAT THE CLOUD PATTERN ASSOCIATED WITH ISABEL
IS GRADUALLY BECOMING BETTER ORGANIZED. IT APPEARS TO BE DEVELOPING
A CENTRAL DENSE OVERCAST AND HAS A WELL DEFINED CURVED BAND. THE
OUTFLOW IS FAIR IN ALL QUADRANTS BUT THE NORTHEAST. THE SHEAR IS
FORECAST TO REMAIN LOW OVER THE TROPICAL ATLANTIC AS INDICATED BY
GLOBAL AND SHIPS MODELS. IN ADDITION...SSTS ARE INCREASING ALONG
THE PATH OF ISABEL. THEREFORE...STRENGHTENING IS INDICATED AND
ISABEL MAY BECOME A HURRICANE IN THE NEXT 2 OR 3 DAYS.

MORE RECENT VISIBLE SATELLITE IMAGES INDICATE THAT THE CENTER
APPEARS TO BE A LITTLE TO THE SOUTH OF PREVIOUSLY INDICATED. BEST
ESTIMATE OF THE INITIAL MOTION IS 270 AT 12 KNOTS. BECAUSE THE
SUBTROPICAL RIDGE IS WELL ESTABLISHED TO THE NORTH OF ISABEL...A
WESTWARD MOTION IS EXPECTED TO CONTINUE. A GRADUAL TURN TO THE
WEST-NORTHWEST IS POSSIBLE IN ABOUT 4 TO 5 DAYS AS THE TROPICAL
CYCLONE APPROACHES A WEAKNESS OF THE RIDGE. THE OFFICIAL FORECAST
IS SIMILAR TO THE LATEST GFS.

FORECASTER AVILA

FORECAST POSITIONS AND MAX WINDS

INITIAL 06/1500Z 13.6N 34.5W 35 KT
12HR VT 07/0000Z 13.7N 36.4W 40 KT
24HR VT 07/1200Z 14.0N 39.0W 45 KT
36HR VT 08/0000Z 14.5N 41.5W 55 KT
48HR VT 08/1200Z 15.0N 44.0W 65 KT
72HR VT 09/1200Z 16.0N 48.0W 65 KT
96HR VT 10/1200Z 17.0N 51.9W 65 KT
120HR VT 11/1200Z 18.0N 56.5W 65 KT

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ZCZC MIATCDAT3 ALL
TTAA00 KNHC DDHHMM
TROPICAL STORM ISABEL DISCUSSION NUMBER 3
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
5 PM EDT SAT SEP 06 2003

SATELLITE IMAGES DURING THE DAY INDICATE THAT ISABEL HAS CONTINUED
TO BECOME BETTER ORGANIZED. THE TROPICAL STORM HAS A LARGE ENVELOPE
DEFINED BY LOW CLOUDS ON SATELLITE...CONVECTIVE CURVED BANDS AND AN
EXPANDING CENTRAL DENSE OVERCAST. THE OUTFLOW CONTINUES TO BE
FAIRLY GOOD IN ALL QUADRANTS BUT THE NORTHEAST. SATELLITE INTENSITY
ESTIMATES AND AN EARLIER ADEOS SCATTEROMETER SUPPORT INCREASING THE
WINDS TO 45 KNOTS. THE OCEAN IS PLENTY WARM AHEAD OF ISABEL AS
INDICATED BY BUOYS AND THE SHEAR IS FORECAST TO REMAIN LOW.
THEREFORE...ISABEL IS FORECAST TO BECOME A HURRICANE.

A 24 TO 36 HOUR SATELLITE LOOP INDICATES THAT ISABEL HAS BEEN MOVING
SOUTH OF DUE WEST...OR PERHAPS IT WAS A REFORMATION UNDER THE
MID-LEVEL CIRCULATION. THE TROPICAL CYCLONE IS FORECAST TO MOVE
ABOUT 10 TO 12 KNOTS TOWARD THE WEST STEERED BY A RATHER STRONG
SUBTROPICAL RIDGE TO THE NORTH. HOWEVER...IN 3 TO 5 DAYS...THE
RIDGE IS EXPECTED TO ERODE AND ISABEL COULD BEGIN TO MOVE TO THE
WEST-NORTHWEST. THE OFFICIAL FORECAST IS SIMILAR TO THE GLOBAL
MODEL CONSENSUS...GUNA...BUT A LITTLE BIT BIASED TOWARD THE GFS.
THE LATTER IS THE ONLY MODEL THAT BRINGS THE TROPICAL CYCLONE VERY
CLOSE TO THE LEEWARD ISLANDS BEYOND 5 DAYS.

FORECASTER AVILA

FORECAST POSITIONS AND MAX WINDS

INITIAL 06/2100Z 13.4N 35.4W 45 KT
12HR VT 07/0600Z 13.4N 36.8W 50 KT
24HR VT 07/1800Z 13.5N 38.5W 60 KT
36HR VT 08/0600Z 14.5N 40.5W 65 KT
48HR VT 08/1800Z 15.5N 43.0W 70 KT
72HR VT 09/1800Z 17.0N 48.5W 75 KT
96HR VT 10/1800Z 18.0N 53.5W 75 KT
120HR VT 11/1800Z 18.5N 58.0W 75 KT

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ZCZC MIATCDAT3 ALL
TTAA00 KNHC DDHHMM
TROPICAL STORM ISABEL DISCUSSION NUMBER 4
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
11 PM EDT SAT SEP 06 2003

SATELLITE IMAGERY DURING THE EVENING SHOWS THAT ISABEL HAS A
WELL-DEFINED CURVED CONVECTIVE BAND WITH TOPS COLDER THAN -80C.
THE CIRRUS OUTFLOW IS EXCELLENT OVER THE SOUTH SEMICIRCLE AND FAIR
TO GOOD ELSEWHERE. SATELLITE INTENSITY ESTIMATES ARE 55 KT FROM
TAFB AND SAB...AND 45 KT FROM AFWA. THE INITIAL INTENSITY IS
RAISED TO 50 KT FOR THIS ADVISORY.

THE INITIAL MOTION IS 270/09. WATER VAPOR IMAGERY INDICATES THAT
ISABEL IS SOUTH OF A MID/UPPER-LEVEL RIDGE...WITH AN UPPER-LEVEL
LOW CENTERED NEAR 26N46W. LARGE-SCALE MODELS SUGGEST THAT THIS LOW
WILL CREATE ENOUGH WEAKNESS IN THE RIDGE TO ALLOW ISABEL TO
GRADUALLY TURN TO A WEST-NORTHWESTWARD COURSE DURING THE NEXT 24-48
HR...AND CONTINUE THAT GENERAL MOTION THROUGH DAY 5. NHC TRACK
GUIDANCE AGREES WITH THIS SCENARIO. SINCE SOME MODELS SHOWED
SOMEWHAT OF A NORTHWARD BIAS WHEN FABIAN WAS IN THIS AREA...THE
OFFICIAL FORECAST WILL LEAN TOWARD THE SOUTH SIDE OF THE GUIDANCE.
IT IS ALSO NUDGED JUST A LITTLE SOUTH OF THE PREVIOUS TRACK.

ISABEL SEEMS TO HAVE ALL THE INGREDIENTS TO STRENGTHEN
SIGNIFICANTLY...A LARGE CYCLONIC ENVELOPE...GOOD CONVECTIVE
STRUCTURE...COLD CLOUD TOPS...AND FAVORABLE OUTFLOW AND VERTICAL
SHEAR. THE SHIPS MODEL TAKES THE STORM TO 80 KT IN 60 HR AND THEN
STOPS INTENSIFICATION FOR REASONS NOT READILY APPARENT. THE GFDL
MAKES ISABEL A 90 KT HURRICANE IN 120 HR. THE INTENSITY FORECAST
WILL SHOW THE INTENSITY LEVELING OFF AT 80 KT IN AGREEMENT WITH THE
SHIPS MODEL. HOWEVER...IT WOULD NOT BE A SURPRISE TO SEE ISABEL
STRENGTHEN FASTER AND MORE THAN CURRENTLY FORECAST.

FORECASTER BEVEN

FORECAST POSITIONS AND MAX WINDS

INITIAL 07/0300Z 13.4N 36.1W 50 KT
12HR VT 07/1200Z 13.4N 37.4W 60 KT
24HR VT 08/0000Z 13.8N 39.4W 65 KT
36HR VT 08/1200Z 14.7N 41.8W 70 KT
48HR VT 09/0000Z 15.6N 44.4W 75 KT
72HR VT 10/0000Z 17.0N 49.4W 80 KT
96HR VT 11/0000Z 18.0N 54.5W 80 KT
120HR VT 12/0000Z 18.5N 59.0W 80 KT
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ZCZC MIATCDAT3 ALL
TTAA00 KNHC DDHHMM
TROPICAL STORM ISABEL DISCUSSION NUMBER 5
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
5 AM EDT SUN SEP 07 2003

OVERNIGHT SATELLITE IMAGERY SHOWS THAT ISABEL CONTINUES TO EXHIBIT A
WELL-DEFINED CURVED CONVECTIVE BAND...AND THE LAST FEW IMAGES
SUGGEST THAT THE CONVECTION HAS BEGUN TO WRAP CLOSER TO THE CENTER.
SATELLITE INTENSITY ESTIMATES ARE A CONSENSUS 55 KT FROM
TAFB...SAB...AND AFWA. THEREFORE...THE INITIAL INTENSITY IS RAISED
TO 55 KT FOR THIS ADVISORY. GLOBAL MODELS SUGGEST THAT A MID/UPPER
LEVEL RIDGE WILL REMAIN NORTH OF THE CYCLONE THROUGH THE FORECAST
PERIOD...PROVIDING FAVORABLE CONDITIONS FOR STRENGTHENING. THE
SHIPS MODEL TAKES ISABEL TO 85 KT IN 72 HOURS...AND THE GFDL BRINGS
THE INTENSITY UP TO 95 KT IN 48 HOURS. THE INTENSITY FORECAST WILL
BE RATHER CONSERVATIVE AND INDICATE GRADUAL STRENGTHENING OVER THE
NEXT 2-3 DAYS...WITH THE INTENSITY LEVELING OFF AT 85 KT BY 72
HOURS WHICH IS IN GENERAL AGREEMENT WITH SHIPS.

THE INITIAL MOTION IS 275/09...SLIGHTLY NORTH OF THE PREVIOUS
ADVISORY. THE SYNOPTIC PATTERN REMAINS BASICALLY UNCHANGED FROM
THE PREVIOUS FORECAST...WITH ISABEL BEING STEERED BY A MID/UPPER
LEVEL RIDGE TO THE NORTH. WATER VAPOR IMAGERY INDICATES AN
UPPER-LEVEL TROUGH ABOUT 900 NM NORTHWEST OF THE TROPICAL CYCLONE.
LARGE-SCALE GLOBAL MODELS SUGGEST THAT THIS TROUGH WILL CREATE JUST
ENOUGH OF A WEAKNESS IN THE RIDGE TO ALLOW FOR A MORE
WEST-NORTHWEST MOTION BEYOND 12 HOURS...AND CONTINUE THAT MOTION
THROUGH DAY 5. NHC TRACK GUIDANCE BASICALLY FOLLOWS THIS
SCENARIO...WITH THE FORECAST TRACK ADJUSTED A TAD TO THE NORTH OF
THE PREVIOUS TRACK AND REMAINING ON THE SOUTH SIDE OF THE GUIDANCE.

FORECASTER MOLLEDA/LAWRENCE

FORECAST POSITIONS AND MAX WINDS

INITIAL 07/0900Z 13.7N 37.1W 55 KT
12HR VT 07/1800Z 13.8N 38.5W 60 KT
24HR VT 08/0600Z 14.8N 40.9W 65 KT
36HR VT 08/1800Z 15.6N 43.2W 70 KT
48HR VT 09/0600Z 16.5N 45.3W 75 KT
72HR VT 10/0600Z 18.0N 50.0W 85 KT
96HR VT 11/0600Z 18.5N 55.5W 85 KT
120HR VT 12/0600Z 19.0N 60.0W 85 KT

Image

HURRICANE ISABEL DISCUSSION NUMBER 6
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
11 AM EDT SUN SEP 07 2003

SATELLITE IMAGERY THIS MORNING INDICATES THAT ISABEL HAS DEVELOPED A
VERY LARGE RAGGED EYE. SATELLITE INTENSITY ESTIMATES ARE 65 KT FROM
TAFB AND SAB...AND 77 KT FROM AFWA...SO THE INITIAL INTENSITY IS
SET AT 65 KT. THE UPPER-LEVEL OUTFLOW PATTERN IS NEARLY CIRCULAR
AND APPEARS TO BE UNRESTRICTED AND EXPANDING.

THE INITIAL MOTION IS 295/09...BASED ON ABOUT A 9 HOUR MOTION
BETWEEN SUCCESSIVE MICROWAVE POSITIONS. THE EYE FEATURE IS RAGGED
AND NOT REALLY A TRUE EMBEDDED EYE. CONVENTIONAL WATER VAPOR AND
SSMI VAPOR SATELLITE IMAGERY INDICATE DRY AIR HAS BEEN WRAPPING
INTO THE CENTER FROM THE SOUTHEAST THROUGH NORTHEAST...WHICH HAS
ACTUALLY ERODED THE CONVECTION ON THE NORTH SIDE. FOR THIS REASON
...THE INITIAL POSITION WAS PLACED NEAR THE SOUTHERN EDGE OF THE
'EYE' AND CLOSER TO THE DEEPEST CONVECTION. EVEN WITH THAT...THE
INITIAL POSITION IS STILL MORE THAN 40 NMI NORTH OF THE PREVIOUS
ADVISORY POSITION. THE GLOBAL MODELS ARE IN FAIRLY GOOD AGREEMENT
AND THERE IS GOOD CONVERGENCE ON A WEST-NORTHWESTWARD TRACK THROUGH
48-72 HOURS...WITH A MORE WESTWARD MOTION AFTER THAT. THIS IS
CONSISTENT WITH THE DEVELOPING SYNOPTIC PATTERN...WHICH INDICATES
THAT THE SUBTROPICAL RIDGE ALONG 32N LATITUDE SHOULD GRADUALLY
SHIFT WESTWARD AND PERHAPS EVEN CLOSE OFF A 500 MB HEIGHT CENTER A
COUPLE HUNDRED MILES SOUTHEAST OF BERMUDA. THE OFFICIAL TRACK IS
SIMILAR TO BUT TO THE RIGHT OF THE PREVIOUS TRACK...MAINLY DUE TO
THE MORE NORTHERLY INITIAL POSITION.

AT LEAST STEADY STRENGTHENING SHOULD OCCUR SINCE ISABEL NOW HAS AN
EYE FEATURE...IS OVER 82F WATER WITH WARMER SSTS AHEAD...AND HAS AN
IMPRESSIVE OUTFLOW PATTERN. BOTH THE SHIPS AND GFDL INTENSITY
MODELS BRING ISABEL UP TO 96 KT IN 42-60 HOURS...SO THIS TREND WAS
CLOSELY FOLLOWED. THE INTENSITY WAS LEVELED OFF AFTER 48 HOURS
SINCE ISABEL IS FORECAST TO BEGIN CROSSING A POSSIBLE COLD WAKE
LEFT BEHIND BY HURRICANE FABIAN LAST WEEK.

FORECASTER STEWART

FORECAST POSITIONS AND MAX WINDS

INITIAL 07/1500Z 14.5N 37.7W 65 KT
12HR VT 08/0000Z 15.1N 39.2W 75 KT
24HR VT 08/1200Z 15.8N 41.3W 85 KT
36HR VT 09/0000Z 16.6N 43.8W 95 KT
48HR VT 09/1200Z 17.3N 46.3W 100 KT
72HR VT 10/1200Z 18.5N 51.0W 100 KT
96HR VT 11/1200Z 19.0N 55.5W 100 KT
120HR VT 12/1200Z 19.5N 60.0W 100 KT

Image

ZCZC MIATCDAT3 ALL
TTAA00 KNHC DDHHMM
HURRICANE ISABEL DISCUSSION NUMBER 7
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
5 PM EDT SUN SEP 07 2003

THE ALLEGED EYE OF ISABEL PASSED OVER BUOY 13008 LOCATED AT 15N 38W
BETWEEN 14-15Z. THE BUOY REPORTED 37 KT AND 24 KT NORTHEAST WINDS
...TO THE SOUTH OF ALL THE SATELLITE CENTER POSITIONS. THESE WIND
REPORTS SUGGEST THAT THE ACTUAL CENTER IS FARTHER SOUTH NEAR THE
SOUTHERN PORTION OF THE EYE FEATURE...AS MENTIONED IN THE PREVIOUS
DISCUSSION. DURING THE PAST 6 HOURS...THE EYE FEATURE...OVERALL
CONVECTIVE PATTERN...AND OUTFLOW PATTERN HAVE CONTINUED TO IMPROVE.
THE INITIAL INTENSITY OF 70 KT IS BASED ON SATELLITE INTENSITY
ESTIMATES OF 65 KT FROM TAFB AND SAB...AND 77 KT FROM AFWA.

THE INITIAL MOTION ESTIMATE IS 295/13. THE INITIAL POSITION REMAINS
ABOUT 24 NMI SOUTH OF THE SATELLITE POSITIONS. THE 12Z GLOBAL
MODELS ARE IN EVEN BETTER AGREEMENT NOW ON KEEPING AT LEAST A
MODERATE SUBTROPICAL RIDGE NORTH OF ISABEL ALONG 32N LATITUDE
THROUGHOUT THE FORECAST PERIOD...AND EVEN BUILD IT WESTWARD ACROSS
THE BAHAMAS AND FLORIDA. THIS SHOULD KEEP ISABEL MOVING
WEST-NORTHWESTWARD THROUGH 48-72 HOURS...WITH A GRADUAL WESTWARD
MOTION DEVELOPING AFTER THAT. THE PREVIOUS FORECAST TRACK WAS ONLY
SHIFTED SLIGHTLY NORTHWARD AND SLOWED A LITTLE AFTER 72 HOURS...
WHICH IS CONSISTENT WITH THE GLOBAL MODEL CONSENSUS.

ISABEL CURRENTLY HAS A VERY IMPRESSIVE OUTFLOW PATTERN AND...
UNFORTUNATELY...THE GLOBAL MODELS ARE FORECASTING IT TO BECOME EVEN
BETTER. BY 36-48 HOURS... ALL OF THE GLOBAL MODELS EXCEPT THE UKMET
ARE FORECASTING MORE THAN 50 KT OF OUTFLOW ON THE WEST SIDE OF
ISABEL BEING DRAWN INTO AN UPPER-LEVEL LOW LOCATED JUST NORTHEAST
OF THE LEEWARD ISLANDS. A PATTERN LIKE THAT CAN OFTENTIMES LEAD TO
RAPID OR EXPLOSIVE DEEPENING. THE SHIPS INTENSITY MODEL BRINGS
ISABEL UP TO 97 KT IN 60 HOURS...BUT THE OFFICIAL FORECAST IS A
LITTLE HIGHER SINCE SHIPS WAS LOW/SLOW WITH THE INTENSIFICATION OF
FABIAN. THE INTENSITY WAS LEVELED OFF AFTER 48 HOURS SINCE ISABEL
MAY CROSS A POSSIBLE COLD WAKE LEFT BEHIND BY HURRICANE FABIAN.

FORECASTER STEWART

FORECAST POSITIONS AND MAX WINDS

INITIAL 07/2100Z 15.2N 39.1W 70 KT
12HR VT 08/0600Z 15.8N 40.5W 75 KT
24HR VT 08/1800Z 16.5N 42.8W 85 KT
36HR VT 09/0600Z 17.2N 45.2W 95 KT
48HR VT 09/1800Z 18.0N 47.7W 100 KT
72HR VT 10/1800Z 19.0N 52.0W 100 KT
96HR VT 11/1800Z 19.5N 55.5W 100 KT
120HR VT 12/1800Z 19.5N 60.0W 100 KT

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Re: Hurricane Isabel

#6 Postby Sciencerocks » Sat May 20, 2023 6:41 pm

CZC MIATCDAT3 ALL
TTAA00 KNHC DDHHMM
HURRICANE ISABEL DISCUSSION NUMBER 8
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
11 PM EDT SUN SEP 07 2003

ISABEL CONTINUES TO GET BETTER ORGANIZED AND HAS IMPRESSIVE COLD
CLOUD TOPS SURROUNDING THE 35 NMI DIAMETER EYE. THE INITIAL
INTENSITY OF 80 KT IS BASED ON SATELLITE INTENSITY ESTIMATES OF 77
KT FROM TAFB AND SAB...AND 90 KT FROM AFWA.

THE INITIAL MOTION ESTIMATE IS 285/13. ISABEL IS MOVING IN THIS
DIRECTION IN RESPONSE TO A SUBTROPICAL RIDGE TO THE NORTH. THE
GLOBAL MODELS ARE ALL IN AGREEMENT THAT THE RIDGE WILL REMAIN
THROUGHOUT THE FORECAST PERIOD AND ISABEL SHOULD CONTINUE TO MOVE
IN A WEST-NORTHWEST TO WEST MOTION FOR THE NEXT FIVE DAYS WITH THE
SYSTEM ENDING UP JUST TO THE NORTHEAST OF THE LEEWARD ISLANDS ON
DAY FIVE. THE OFFICIAL FORECAST REFLECTS THIS AND IS ESSENTIALLY AN
UPDATE OF THE PREVIOUS FORECAST.

THE SHIPS MODEL SEEMS TO BE HANDLING THE INTENSIFICATION OF ISABEL
VERY WELL SO THE INTENSITY FORECAST BASICALLY FOLLOWS THE SHIPS
GUIDANCE.

FORECASTER JARVINEN

FORECAST POSITIONS AND MAX WINDS

INITIAL 08/0300Z 16.1N 40.2W 80 KT
12HR VT 08/1200Z 16.8N 42.0W 85 KT
24HR VT 09/0000Z 17.7N 44.4W 90 KT
36HR VT 09/1200Z 18.5N 46.9W 95 KT
48HR VT 10/0000Z 19.2N 49.3W 100 KT
72HR VT 11/0000Z 19.7N 53.2W 100 KT
96HR VT 12/0000Z 20.2N 56.7W 100 KT
120HR VT 13/0000Z 20.5N 60.0W 100 KT


NNNN
https://www.youtube.com/watch?v=wdRbed7ZUjg

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HURRICANE ISABEL DISCUSSION NUMBER 9
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
5 AM EDT MON SEP 08 2003

ISABEL CONTINUES TO GET BETTER ORGANIZED AND HAS IMPRESSIVE COLD
CLOUD TOPS SURROUNDING THE EYE WHICH HAS DECREASED IN DIAMETER SINCE
THE LAST ADVISORY. THE INITIAL INTENSITY IS NOW 90 KT AND IS BASED
ON SATELLITE INTENSITY ESTIMATES OF 102 KTS FROM TAFB AND 90 KTS
FROM SAB AND AIR FORCE GLOBAL. IN FACT...ISABEL MAY BE STRONGER BUT
I WANT TO SEE IF IT CAN MAINTAIN THESE SATELLITES ESTIMATES FOR AT
LEAST ANOTHER CYCLE BEFORE I GO ABOVE 90 KTS

THE INITIAL MOTION ESTIMATE IS 300/14. ISABEL IS MOVING IN THIS
DIRECTION IN RESPONSE TO A SUBTROPICAL RIDGE TO THE NORTH. BUT...
WATER VAPOR IMAGERY ALSO SHOWS AN UPPER COLD LOW THAT IS DEVELOPING
TO THE WEST OF ISABEL. THE SOUTHERLY AND SOUTHWESTERLY FLOW ON THE
EAST SIDE OF THIS COLD LOW MAY BE ADDING A NORTHERLY COMPONENT TO
THE MOTION. HOWEVER...THE GLOBAL MODELS EVENTUALLY MOVE THIS
SYSTEM TOWARD THE WEST AND WEAKEN IT. THE GLOBAL MODELS ARE ALL IN
AGREEMENT THAT THE RIDGE WILL REMAIN THROUGHOUT THE FORECAST PERIOD
AND ISABEL SHOULD CONTINUE TO MOVE IN A WEST-NORTHWEST TO WEST
MOTION FOR THE NEXT FIVE DAYS WITH THE SYSTEM ENDING UP JUST TO THE
NORTHEAST OF THE LEEWARD ISLANDS ON DAY FIVE. THE OFFICIAL FORECAST
REFLECTS THIS AND IS ESSENTIALLY AN UPDATE OF THE PREVIOUS
FORECAST.

THE SHIPS MODEL INTENSIFIES ISABEL TO 115 KTS IN 48 HOURS AND THE
OFFICIAL INTENSITY FORECAST REFLECTS THIS. HOWEVER...THE SYSTEM
MAY BE IN A RAPID DEEPENING MODE AND MAY GET STRONGER SOONER.

FORECASTER JARVINEN

FORECAST POSITIONS AND MAX WINDS

INITIAL 08/0900Z 16.9N 41.4W 90 KT
12HR VT 08/1800Z 17.9N 43.3W 100 KT
24HR VT 09/0600Z 18.8N 45.7W 105 KT
36HR VT 09/1800Z 19.4N 48.0W 110 KT
48HR VT 10/0600Z 19.8N 50.3W 115 KT
72HR VT 11/0600Z 19.9N 54.4W 115 KT
96HR VT 12/0600Z 20.2N 58.0W 115 KT
120HR VT 13/0600Z 20.6N 60.7W 115 KT

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ZCZC MIATCDAT3 ALL
TTAA00 KNHC DDHHMM
HURRICANE ISABEL DISCUSSION NUMBER 10
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
11 AM EDT MON SEP 08 2003

ISABEL HAS CONTINUED TO RAPIDLY INTENSIFY. THE INITIAL INTENSITY IS
INCREASED TO 100 KT BASED ON SATELLITE INTENSITY ESTIMATES OF 115
KT FROM TAFB AND AFWA...102 KT FROM SAB...AND 102 KT/T5.5 3-HOUR
OBJECTIVE DVORAK INTENSITY ESTIMATES. THE 100 KT INITIAL INTENSITY
IS ALSO CONSISTENT WITH THE LATEST AMSU INTENSITY ESTIMATES OF 100
KT AND 960 MB. OUTFLOW REMAINS QUITE IMPRESSIVE AND CONTINUES TO
IMPROVE AND THE EYE DIAMETER HAS DECREASED DOWN TO 25 NMI.

THE INITIAL MOTION ESTIMATE IS 290/12. IS APPEARS THAT ISABEL MAY BE
MAKING THE MORE WESTWARD TURN THAT THE GLOBAL MODELS HAVE BEEN
INDICATING. THE NHC MODEL GUIDANCE IS EVEN MORE TIGHTLY PACKED AND
IN GOOD AGREEMENT ON ISABEL MOVING WEST-NORTHWESTWARD FOR THE NEXT
36 HOURS...AND THEN TURNING MORE WESTWARD AFTER THAT. THIS IS QUITE
REASONABLE GIVEN THE STRENGTH AND EAST-WEST ORIENTATION OF THE
SUBTROPICAL RIDGE LOCATED ALONG 32N LATITUDE. A DISCONCERTING PART
OF THE MODEL GUIDANCE IS THE GFS AND NOGAPS MODELS CONTINUING TO
INSIST THAT ISABEL WILL MAKE A DIP SOUTH-OF-WEST AFTER 72 HOURS.
THEY BRING ISABEL DANGEROUSLY CLOSE TO THE NORTHERN LEEWARD ISLANDS
BY 120 HOURS. THE GFS AND NOGAPS HAD A LEFT OF TRACK BIAS WITH
FABIAN LAST WEEK...SO I PREFER TO WAIT ANOTHER 24 HOURS OR SO TO
SEE IF THIS SAME BIAS DEVELOPS. HOWEVER...THIS SCENARIO CAN NOT BE
COMPLETELY RULED OUT GIVEN THE DEEP MID-/UPPER-LEVEL TROUGH
NORTHWEST OF AFRICA THAT HAS BEEN DIGGING SOUTHWESTWARD. THAT COULD
CREATE ENOUGH LOW-LEVEL RIDGING FROM THE NORTHEAST TO NUDGE ISABEL
A LITTLE SOUTH OF DUE WEST...SIMILAR TO THE GFS-NOGAPS SCENARIO.

ISABEL IS ABOUT 18-24 HOURS INTO A RAPID INTENSIFICATION CYCLE...SO
THIS TREND IS FORECAST TO CONTINUE FOR ANOTHER 12 HOURS OR SO.
AFTER REACHING CATEGORY 4 INTENSITY...INNER-CORE CONVECTION AND
EYEWALL DYNAMICS WILL DICTATE ANY INTENSITY CHANGES. HOWEVER...THE
INTENSITY FORECAST COULD EASILY BE TOO LOW GIVEN THE CURRENT AND
FORECAST OUTFLOW PATTERN THAT WILL EVOLVE OVER THE NEXT 48 HOURS.

FORECASTER STEWART

FORECAST POSITIONS AND MAX WINDS

INITIAL 08/1500Z 17.2N 42.6W 100 KT
12HR VT 09/0000Z 17.9N 44.4W 115 KT
24HR VT 09/1200Z 18.6N 46.8W 120 KT
36HR VT 10/0000Z 19.2N 49.1W 120 KT
48HR VT 10/1200Z 19.4N 51.1W 120 KT
72HR VT 11/1200Z 19.5N 55.0W 120 KT
96HR VT 12/1200Z 19.5N 58.5W 120 KT
120HR VT 13/1200Z 20.0N 62.5W 120 KT
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HURRICANE ISABEL DISCUSSION NUMBER 11
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
5 PM EDT MON SEP 08 2003

ISABEL HAS CONTINUED ITS RAPID INTENSIFICATION TREND. THE INITIAL
INTENSITY IS INCREASED TO 110 KT BASED ON SATELLITE INTENSITY
ESTIMATES OF 115 KT FROM TAFB AND AFWA...102 KT FROM SAB...AND 113
KT/T5.9 3-HOUR OBJECTIVE DVORAK INTENSITY ESTIMATES. THE OUTFLOW
REMAINS VERY IMPRESSIVE AND THE OVERALL CONVECTIVE PATTERN HAS ALSO
CONTINUED TO IMPROVE.

THE INITIAL MOTION ESTIMATE IS 295/12. THERE HAS BEEN SOME WOBBLING
ALONG THE TRACK THE PAST 6 HOURS...WHICH IS TYPICAL OF INTENSE
HURRICANES. THE NHC MODEL GUIDANCE REMAINS IN GOOD AGREEMENT ON
ISABEL MOVING WEST-NORTHWESTWARD FOR THE NEXT 36 HOURS OR SO...AND
THEN TURNING MORE WESTWARD AFTER THAT. HOWEVER...THE GFS AND NOGAPS
MODELS MAINTAIN A WEST-SOUTHWESTWARD MOTION AFTER 48-72 HOURS. THE
REASON FOR THIS MORE SOUTHERLY TRACK IS NOT APPARENT IN THE MODEL
FIELDS...SO I AM CONTINUING TO PLACE LESS WEIGHT ON THAT SCENARIO
AT THIS TIME BASED ON THOSE MODELS HAVING A PREVIOUS LEFT-BIAS WITH
FABIAN. THE OFFICIAL FORECAST TRACK IS NUDGED SLIGHTLY NORTH OF THE
PREVIOUS TRACK THROUGH 36 HOURS...AND THEN COMES BACK ON TRACK
AFTER THAT. THIS IS CONSISTENT WITH THE GLOBAL MODEL CONSENSUS.

ISABEL IS 24 HOURS INTO A RAPID INTENSIFICATION CYCLE...BUT RARELY
DUE SUCH TRENDS OCCUR FOR MORE THAN 30-36 HOURS. THEREFORE...THE
CURRENT INTENSIFICATION TREND IS LEVELED OFF AFTER ABOUT 12 HOURS
OR SO. HOWEVER...UPPER-LEVEL CONDITIONS ARE FORECAST TO REMAIN
QUITE FAVORABLE THROUGHOUT THE FORECAST PERIOD...SO ISABEL COULD
STILL REACH CATEGORY 4 INTENSITY DURING THE NEXT 12 HOURS OR SO.
AFTER THAT...INNER-CORE CONVECTION AND EYEWALL DYNAMICS WILL
DICTATE ANY FURTHER INTENSITY CHANGES. HOWEVER...THE INTENSITY
FORECAST COULD EASILY BE TOO LOW GIVEN THAT THE OUTFLOW PATTERN IS
EXPECTED TO CONTINUE TO IMPROVE...THE VERTICAL SHEAR IS FORECAST TO
REMAIN LESS THAN 10 KT...AND ISABEL WILL BE MOVING OVER 28C AND
WARMER SSTS.

FORECASTER STEWART

FORECAST POSITIONS AND MAX WINDS

INITIAL 08/2100Z 17.9N 43.7W 110 KT
12HR VT 09/0600Z 18.6N 45.6W 120 KT
24HR VT 09/1800Z 19.2N 47.9W 125 KT
36HR VT 10/0600Z 19.5N 50.0W 125 KT
48HR VT 10/1800Z 19.5N 52.0W 125 KT
72HR VT 11/1800Z 19.5N 55.5W 125 KT
96HR VT 12/1800Z 19.5N 59.0W 125 KT
120HR VT 13/1800Z 20.0N 63.0W 125 KT

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HURRICANE ISABEL DISCUSSION NUMBER 12
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
11 PM EDT MON SEP 08 2003

DVORAK INTENSITY CLASSIFICATIONS FROM TAFB AND SAB WERE T6.0 OR 115
KT...AND THAT WILL BE THE ADVISORY INTENSITY. ISABEL HAS AN
IMPRESSIVE OUTFLOW PATTERN ALTHOUGH IT IS BEING SQUEEZED A LITTLE
BIT IN THE SOUTHWEST QUADRANT BY THE UPPER-LEVEL LOW TO ITS WEST.

THE INITIAL MOTION ESTIMATE IS 300/11. THERE IS A SPLIT IN THE
MODEL GUIDANCE THAT HAS SOME BEARING ON THE POTENTIAL THREAT TO THE
NORTHERN LEEWARD ISLANDS. WHILE THE CANADIAN AND UKMET MODELS BEND
THE TRACK ONLY SLIGHTLY TO THE LEFT FROM 24-72 HOURS...THE GFS AND
NOGAPS TURN THE TRACK HARDER...TO THE WEST-SOUTHWEST OR EVEN
SOUTHWEST...WHICH BRINGS THE CENTER UNCOMFORTABLY CLOSE TO THESE
ISLANDS. ONE DIFFERENCE IN THESE MODEL SOLUTIONS IS HOW STRONGLY
ISABEL INTERACTS WITH THE MID TO UPPER-LEVEL LOW CURRENTLY
APPROACHING THE HURRICANE FROM THE NORTHEAST...AS WELL AS THE
MID-LEVEL VORTEX ASSOCIATED WITH TROPICAL DEPRESSION FOURTEEN. IN
THE UKMET AND CANADIAN MODELS THERE IS NO APPRECIABLE
INTERACTION...WHILE IN THE GFS AND NOGAPS THE LOW IS CLOSE ENOUGH
TO DRAG ISABEL SOUTHWARD. IN PART BECAUSE OF THE IMPRESSIVE
ANTICYCLONIC OUTFLOW IN THE NORTHEAST QUADRANT OF ISABEL...AND THE
CURRENT DISARRAY OF TD FOURTEEN...MY FEELING IS THAT THE
INTERACTION IS BEING OVERDONE BY THE GFS AND NOGAPS. THE OFFICIAL
FORECAST IS VERY CLOSE TO THE GLOBAL MODEL CONSENSUS AND GFDL
SOLUTIONS...AND SLIGHTLY TO THE RIGHT OF THE PREVIOUS FORECAST.

I HAVE BACKED OFF A BIT FROM THE INTENSITY FORECAST OF THE PREVIOUS
ADVISORY. SST ANALYSES SHOW THAT ISABEL WILL BE PASSING OVER THE
COOL WAKE OF FABIAN IN ABOUT 36 HOURS...AND THERE COULD BE SOME
RESTRICTION OF THE OUTFLOW BY THE UPPER LOW APPROACHING FROM THE
NORTHEAST...EVEN IF THAT LOW DOES NOT COME CLOSE ENOUGH TO
APPRECIABLY AFFECT THE TRACK. IT IS ALSO QUITE RARE FOR STORMS TO
MAINTAIN MAJOR HURRICANE STATUS FOR FIVE DAYS. EVEN WITH THIS
ADJUSTMENT...THE OFFICIAL FORECAST REMAINS ABOVE THE GFDL AND SHIPS
INTENSITY GUIDANCE.

FORECASTER FRANKLIN

FORECAST POSITIONS AND MAX WINDS

INITIAL 09/0300Z 18.5N 44.5W 115 KT
12HR VT 09/1200Z 19.2N 46.2W 120 KT
24HR VT 10/0000Z 19.9N 48.5W 125 KT
36HR VT 10/1200Z 20.0N 50.6W 120 KT
48HR VT 11/0000Z 20.0N 52.5W 115 KT
72HR VT 12/0000Z 20.0N 56.0W 110 KT
96HR VT 13/0000Z 20.0N 59.5W 110 KT
120HR VT 14/0000Z 21.0N 63.0W 110 KT

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Sciencerocks
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Re: Hurricane Isabel

#7 Postby Sciencerocks » Sat May 20, 2023 6:48 pm

CZC MIATCDAT3 ALL
TTAA00 KNHC DDHHMM
HURRICANE ISABEL DISCUSSION NUMBER 13
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
5 AM EDT TUE SEP 09 2003

06Z DVORAK SUBJECTIVE INTENSITY ESTIMATES WERE T NUMBER 6.0 OR 115
KNOT FROM ALL AGENCIES AND OBJECTIVE T NUMBERS WERE THE SAME. THE
WELL-DEFINED EYE AND CLOUD STRUCTURE REMAIN IMPRESSIVE. THE
OFFICIAL INITIAL AND FORECAST INTENSITIES ARE IDENTICAL TO THE
PREVIOUS ADVISORY...TO 125 KNOTS IN 24 HOURS FOLLOWED BY SLOW
WEAKENING. THE GLOBAL MODELS SHOW LITTLE CHANGE IN INTENSITY IN THE
NEXT 5 DAYS. HOWEVER HURRICANES RARELY MAINTAIN SUCH A HIGH WIND
SPEED FOR FIVE DAYS AND THE SHIPS MODEL SHOWS WEAKENING AFTER 60
HOURS BECAUSE OF THIS FACTOR. FABIANS COOL WAKE COULD ALSO BE A
NEGATIVE FACTOR.

THE INITIAL MOTION IS 300/12. THE GFS SHOWS A STRONG SOUTHWARD
BUILDING OF THE SUBTROPICAL RIDGE AHEAD OF ISABEL AND THE TRACK
MODELS RESPOND BY SHOWING A TURN TOWARD THE SOUTHWEST DURING DAY 1
THROUGH 3 FOLLOWED BY A SMALLER WESTWARD TURN ON DAY 4 OR 5. THE
OFFICIAL FORECAST TRACK FOLLOWS A MODEL CONCENSUS AND IS SIMILAR TO
THE PREVIOUS ADVISORY FORECAST.

THE CENTER OF ISABEL IS FORECAST TO MOVE TO WITH ABOUT 200 MILES
NORTH OF THE NORTHEASTERNMOST ISLANDS OF THE CARIBBEAN ON DAYS 4
AND 5. THE AVERAGE ERRORS OF 4 AND 5 DAY TRACK FORECASTS ARE MORE
THAN 200 MILES.

FORECASTER LAWRENCE

FORECAST POSITIONS AND MAX WINDS

INITIAL 09/0900Z 19.1N 45.7W 115 KT
12HR VT 09/1800Z 19.8N 47.5W 120 KT
24HR VT 10/0600Z 20.3N 49.4W 125 KT
36HR VT 10/1800Z 20.3N 51.3W 120 KT
48HR VT 11/0600Z 20.0N 53.3W 115 KT
72HR VT 12/0600Z 19.5N 56.5W 110 KT
96HR VT 13/0600Z 20.0N 59.5W 110 KT
120HR VT 14/0600Z 21.0N 63.0W 110 KT
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CZC MIATCDAT3 ALL
TTAA00 KNHC DDHHMM
HURRICANE ISABEL DISCUSSION NUMBER 14
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
11 AM EDT TUE SEP 09 2003

SATELLITE INTENSITY ESTIMATES FROM ALL THREE AGENCIES REMAIN AT 115
KT. THE EYE BECAME CLOUD-COVERED EARLIER THIS MORNING...BUT OVER
THE PAST 3 HOURS THE EYE HAS CLEARED OUT...BECOME BETTER DEFINED
...AND EYEWALL CONVECTIVE CLOUD TOPS HAVE STARTED TO COOL.
THEREFORE...THE INITIAL INTENSITY REMAINS AT 115 KT FOR THIS
ADVISORY...DESPITE THE WEAKENING TREND INDICATED BY THE 3-HOUR
OBJECTIVE T-NUMBERS.

THE INITIAL MOTION ESTIMATE IS 300/12. ISABEL HAS BEEN MAINTAINING A
STEADY WEST-NORTHWESTWARD MOTION FOR THE PAST 48 HOURS...DESPITE
MOST OF THE NHC MODEL GUIDANCE FORECASTING A TURN MORE TOWARD THE
WEST. IT APPEARS THAT ISABEL IS BEING INFLUENCED BY THE SOUTHERLY
FLOW ON THE EAST SIDE OF A LARGE MID-/UPPER-LOW JUST NORTH OF THE
LEEWARD ISLANDS. THIS LOW IS FORECAST BY ALL THE GLOBAL MODELS TO
MOVE QUICKLY NORTHWESTWARD AND WEAKEN DURING THE NEXT 48-72 HOURS.
THE WEAKENING OF THE LOW COMBINED WITH A BUILDING MID-LEVEL RIDGE
NEAR BERMUDA SHOULD ALLOW ISABEL TO MOVE IN A WESTWARD MOTION BY 24
HOURS OR SO. THE GFDL...GFS...AND NOGAPS MODEL CONTINUE TO FORECAST
A SHARP WEST-SOUTHWESTWARD MOTION AFTER 36 HOURS. OUT OF RESPECT
FOR THESE MODELS...A SLIGHT SOUTHWARD JOG IS INDCIATED IN THE
FORECAST TRACK. THE UKMET...HOWEVER...MODEL IS NOT FORECASTING THAT
SOUTHWARD JOG. THE OFFICIAL FORECAST TRACK IS ESSENTIALLY AN UPDATE
OF THE PREVIOUS TRACK AND IS CLOSE TO THE NHC MODEL CONSENSUS.

THE UPPER-LEVEL OUTFLOW PATTERN REMAINS QUITE IMPRESSIVE...
ESPECIALLY WITH THE DEEPENING TROUGH TO THE EAST OF ISABEL
ENHANCING THE OUTFLOW IN THE EASTERN SEMICIRCLE...WHILE THE LARGE
UPPER-LEVEL LOW TO THE WEST IS ENHANCING THE OUTFLOW IN THAT AREA.
THIS FAVORABLE OUTFLOW PATTERN IS FORECAST TO PERSIST FOR AT LEAST
ANOTHER 48 HOURS...SO SOME ADDITIONAL STRENGTHENING IS POSSIBLE.
GIVEN THAT ISABEL IS ALREADY A CAT 4 HURRICANE...SPECIFIC
INTENSIFICATION WILL BE DICTATED BY EYEWALL DYNAMICS LIKE EYEWALL
REPLACEMENT CYCLES THAT CAN NOT BE FORECAST WITH ANY SKILL.

FORECASTER STEWART

FORECAST POSITIONS AND MAX WINDS

INITIAL 09/1500Z 19.6N 46.9W 115 KT
12HR VT 10/0000Z 20.1N 48.4W 120 KT
24HR VT 10/1200Z 20.3N 50.3W 125 KT
36HR VT 11/0000Z 20.2N 52.3W 120 KT
48HR VT 11/1200Z 19.9N 54.0W 115 KT
72HR VT 12/1200Z 20.0N 57.0W 115 KT
96HR VT 13/1200Z 20.5N 60.5W 110 KT
120HR VT 14/1200Z 21.0N 64.5W 110 KT

HURRICANE ISABEL DISCUSSION NUMBER 15
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
5 PM EDT TUE SEP 09 2003

SATELLITE INTENSITY ESTIMATES FROM ALL THREE AGENCIES REMAIN AT 115
KT. THE EYE HAS BECOME CLOUD-COVERED THIS AFTERNOON...BUT OVER
THE PAST 2 HOURS THE EYE HAS CLEARED OUT AND WARMED SOME. ALSO...
EYEWALL CLOUD TOPS HAVE COOLED SIGNIFICANTLY WITH SOME TOPS AS COLD
AS -80C TO -85C. OBJECTIVE DVORAK T-NUMBERS HAVE ALSO INCREASED TO
115 KT AND SLIGHTLY HIGHER IN THE LAST COUPLE OF HOURS...SO IT IS
POSSIBLE THAT ISABEL HAS STRENGTHENED A LITTLE. HOWEVER...I WOULD
PREFER TO WAIT ANOTHER FEW HOURS TO SEE IF THE EYE CLEARS OUT
BEFORE INCREASING THE INTENSITY.

THE INITIAL MOTION ESTIMATE IS 300/11. ISABEL HAS BEEN MAINTAINING A
STEADY WEST-NORTHWESTWARD MOTION FOR THE PAST 2-3 DAYS AND ALL OF
THE NHC MODEL GUIDANCE HAS HAD A PROFOUND LEFT-OF-TRACK BIAS...
ESPECIALLY THE GFS AND NOGAPS MODELS. THEREFORE...IT IS TIME TO
BAIL OUT ON THE MODEL CONSENSUS AND SHIFT THE FORECAST TRACK CLOSER
TO THE MORE NORTHERN GFDL AND UKMET SOLUTIONS. THE OFFICIAL
FORECAST TRACK IS SIGNIFICANTLY NORTH OF THE PREVIOUS FORECAST
TRACKS...BUT IT WAS NOT SHIFTED AS FAR NORTH AS THE UKMET SOLUTION.
THE MAIN REASON IS THAT THE LARGE MID-/UPPER-LOW JUST NORTH OF THE
LEEWARD ISLANDS HAS BECOME ELONGATED EAST-WEST DURING THE PAST 6
HOURS AND THE FLOW ON THE EAST SIDE OF THE LOW HAS SHIFTED FROM A
SOUTHERLY DIRECTION TO MORE SOUTHEASTERLY. THIS SHOULD IMPART LESS
OF A NORTHWARD COMPONENT TO ISABEL WITH TIME AS THE LOW CONTINUES
MOVE QUICKLY NORTHWESTWARD AND WEAKEN. ON A LARGER SCALE...THE
MID-LATITUDE FLOW OVER NORTH AMERICA IS FORECAST TO AMPLIFY OVER
THE NEXT 5 DAYS WITH A LARGE RIDGE OFF THE U.S. WEST COAST AND A
DEEP TROUGH OVER THE CENTRAL U.S. THE RESULTING PATTERN SHOULD
BUILD AND MAINTAIN A RIDGE ALONG AND EAST OF THE U.S. EAST
COAST...WHICH SHOULD ACT TO KEEP ISABEL MOVING IN A GENERAL
WESTWARD DIRECTION. BY DAY 5...THE STEERING FLOW IS FORECAST TO
WEAKEN AS A WEAK SHORTWAVE TROUGH DEVELOPS OVER THE SOUTHEAAST U.S.
AND ERODES THE RIDGE A LITTLE TO THE NORTHWEST OF ISABEL.

THE UPPER-LEVEL OUTFLOW PATTERN IS FORECAST TO REMAIN VERY FAVORABLE
FOR AT LEAST ANOTHER 48 HOURS...SO SOME ADDITIONAL STRENGTHENING IS
STILL POSSIBLE. GIVEN THAT SATELLITE INTENSITY ESTIMATES ARE
NEARING T6.5...127 KT...SOME INTENSIFICATION IS PROBABLE TONIGHT.

FORECASTER STEWART

FORECAST POSITIONS AND MAX WINDS

INITIAL 09/2100Z 20.3N 47.8W 115 KT
12HR VT 10/0600Z 21.1N 49.4W 120 KT
24HR VT 10/1800Z 21.6N 51.4W 125 KT
36HR VT 11/0600Z 21.7N 53.1W 120 KT
48HR VT 11/1800Z 21.8N 54.6W 115 KT
72HR VT 12/1800Z 21.9N 57.5W 115 KT
96HR VT 13/1800Z 22.0N 60.5W 110 KT
120HR VT 14/1800Z 23.0N 64.0W 110 KT
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ZCZC MIATCDAT3 ALL
TTAA00 KNHC DDHHMM
HURRICANE ISABEL DISCUSSION NUMBER 16
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
11 PM EDT TUE SEP 09 2003

THERE HAS BEEN SOME EROSION OF THE EYEWALL CONVECTION IN THE EASTERN
SEMICIRCLE AND THE EYE HAS BECOME LESS DISTINCT OVER THE PAST FEW
HOURS. WATER VAPOR IMAGERY ALSO INDICATES THAT THE OUTFLOW TO THE
NORTHEAST OF ISABEL IS BECOMING SLIGHTLY RESTRICTED. DVORAK T
NUMBERS ARE 5.5 FROM TAFB AND SAB...AND THE 3-HR AVERAGE RAW ODT IS
ALSO DOWN TO 5.4. THE INITIAL INTENSITY WILL BE HELD AT 115 KT FOR
THIS ADVISORY.

THE INITIAL MOTION ESTIMATE...BASED ON THE LAST 12 HOURS...IS
295/12...ALTHOUGH OVER THE PAST THREE HOURS THE MOTION HAS BEEN
TOWARD THE WEST. THIS IS QUITE POSSIBLY THE BEGINNING OF THE
EXPECTED WESTWARD TURN...BUT THREE HOURS OF MOTION IS NOT ENOUGH TO
BE SURE...ESPECIALLY GIVEN THE DEGRADATION OF THE EYE OBSERVED
DURING THIS PERIOD. REGARDLESS...ISABEL IS SOUTH OF A MID-LEVEL
RIDGE OF HIGH PRESSURE THAT SHOULD FORCE THE HURRICANE ON A
GENERALLY WESTWARD TRACK OVER THE NEXT THREE DAYS. AFTER THAT...
GLOBAL MODELS GENERALLY SHOW A BREAK IN THE RIDGE BETWEEN 75 AND
80W THAT WOULD ALLOW A TURN BACK TO THE WEST-NORTHWEST ON DAYS 4
AND 5 OF THE FORECAST.

FOR THE LAST COUPLE OF DAYS...THE GUIDANCE ENVELOPE HAS BEEN
CONSISTENTLY DEFINED BY THE UKMET ON THE NORTH AND THE GFS/NOGAPS
ON THE SOUTH. AMONG THE GLOBAL MODELS...THE UKMET HAS BEEN THE BEST
PERFORMER SO FAR WITH ISABEL AND THE GFS HAS BEEN THE WORST. THE
UKMET ALSO WAS THE BEST OF THE GLOBAL MODELS FOR FABIAN. THE
INITIAL VORTEX FOR ISABEL IN THE GFS HAS BEEN CONSISTENTLY MUCH
WEAKER THAN THE INITIALIZATION IN THE UKMET...ALTHOUGH I AM NOT
CERTAIN THAT THIS EXPLAINS THE DIFFERENCES BETWEEN THE TWO MODELS.
GIVEN THE RECENT MOTION...I HAVE NUDGED THE OFFICIAL FORECAST TRACK
A LITTLE SOUTH OF THE PREVIOUS ADVISORY. THE NEW TRACK IS IN BEST
AGREEMENT WITH THE GFDL...AND SLIGHTLY ON THE UKMET SIDE OF THE
GLOBAL MODEL CONSENSUS.

ENVIRONMENTAL CONDITIONS SHOULD BE GENERALLY FAVORABLE FOR THE NEXT
SEVERAL DAYS...SO LITTLE OVERALL CHANGE IN STRENGTH IS FORECAST.
HOWEVER...FLUCTUATIONS IN INTENSITY ARE COMMON IN MAJOR HURRICANES
AND THESE ARE GENERALLY VERY DIFFICULT TO FORECAST.

FORECASTER FRANKLIN

FORECAST POSITIONS AND MAX WINDS

INITIAL 10/0300Z 20.6N 48.8W 115 KT
12HR VT 10/1200Z 21.3N 50.4W 115 KT
24HR VT 11/0000Z 21.5N 52.3W 115 KT
36HR VT 11/1200Z 21.5N 53.9W 115 KT
48HR VT 12/0000Z 21.5N 55.5W 115 KT
72HR VT 13/0000Z 21.5N 58.5W 115 KT
96HR VT 14/0000Z 22.0N 61.5W 110 KT
120HR VT 15/0000Z 23.0N 65.0W 110 KT

ZCZC MIATCDAT3 ALL
TTAA00 KNHC DDHHMM
HURRICANE ISABEL DISCUSSION NUMBER 17
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
5 AM EDT WED SEP 10 2003

SATELLITE IMAGES SHOW A DISTINCT EYE SURROUNDED BY DEEP CONVECTION.
THE OUTFLOW TO THE WEST AND SOUTH IS IMPRESSIVE BUT IS SOMEWHAT
LIMITED TO THE EAST. SUBJECTIVE T-NUMBERS ARE 6.0 AND 5.5 FROM TAFB
AND SAB..RESPECTIVELY. THE LATEST OBJECTIVE T-NUMBERS ARE BACK UP
TO 6.0 ON THE DVORAK SCALE. INITIAL INTENSITY REMAINS AT 115 KNOTS.
THERE IS NO SHEAR AND THE OCEAN IS INCREASINGLY WARMER. THESE
ENVIRONMENTAL CONDITIONS SHOULD ALLOW SOME ADDITIONAL
STRENGTHENING. BUT...IN MAJOR HURRICANES...CHANGES IN INTENSITY ARE
CONTROLLED IN GENERAL BY EYEWALL THERMODYNAMICS. THEREFORE...SOME
FLUCTUATIONS IN INTENSITY ARE INDICATED TO REFLECT UNCERTAINTIES.

THE FORECAST TRACK IS BECOMING RATHER INTERESTING. LAST FEW
SATELLITE IMAGES SUGGEST THAT ISABEL HAS BEGUN TO TURN TOWARD THE
WEST. THE INITIAL MOTION IS NOW ESTIMATED AT 275 DEGREES AT 12
KNOTS. HOWEVER...A LONGER TERM AVERAGE IS STILL TOWARD THE
WEST-NORTHWEST. GLOBAL MODELS CONTINUE TO SHOW THE DEVELOPMENT OF A
STRONG SUBTROPICAL RIDGE NORTH OF ISABEL. DEPENDING UPON THE
FORECAST STRENGTH OF THE RIDGE...EACH MODEL MOVES ISABEL EITHER
WEST OR WEST-NORTHWEST. THE GFS HAS THE STRONGEST RIDGE AND IS
PRODUCING THE SOUTHERMOST AND DANGEROUS TRACK. THE UK HAS A WEAKER
RIDGE WITH THE NORTHERMOST TRACK BUT STILL INDICATING A
WEST-NORTHWEST TO WEST MOTION. THE OFFICIAL FORECAST IS IN BETWEEN
THESE TWO SOLUTIONS. THE NOGAPS APPEARS TO BE VERY SLOW BUT IT IS
SHOWING THE SAME WEST TO WEST-NORTHWEST TREND. THE BOTTOM LINE IS
THAT A RIDGE IS FORECAST TO DEVELOP BETWEEN THE U.S. EAST COAST AND
BERMUDA. THIS PATTERN WOULD MAINTAIN ISABEL ON A GENERAL WEST TO
WEST-NORTHWEST TRACK FOR THE NEXT SEVERAL DAYS...KEEPING THE CORE
OF THE HURRICANE AWAY FROM THE NORTHERN LEEWARD ISLANDS.

IF THE CURRENT WESTWARD TREND CONTINUES...THE OFFICIAL FORECAST WILL
HAVE TO BE ADJUSTED SLIGHTLY SOUTHWARD IN THE NEXT TERM.

FORECASTER AVILA

FORECAST POSITIONS AND MAX WINDS

INITIAL 10/0900Z 20.9N 50.2W 115 KT
12HR VT 10/1800Z 21.5N 52.1W 115 KT
24HR VT 11/0600Z 21.5N 54.2W 115 KT
36HR VT 11/1800Z 21.5N 56.0W 115 KT
48HR VT 12/0600Z 21.5N 58.0W 115 KT
72HR VT 13/0600Z 21.5N 60.5W 115 KT
96HR VT 14/0600Z 22.0N 63.5W 110 KT
120HR VT 15/0600Z 23.0N 67.0W 110 KT

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HURRICANE ISABEL DISCUSSION NUMBER 18
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
11 AM EDT WED SEP 10 2003

SATELLITE IMAGERY INDICATES ANOTHER STRONG CONVECTIVE BURST HAS
DEVELOPED IN THE NORTHERN EYEWALL. THIS HAS SENT CIRRUS CLOUDS
SPREADING SOUTHWARD AND OBSCURING THE NORTHERN HALF OF THE LARGE
EYE. THEREFORE...THE INITIAL POSITION IS JUST A TAD NORTH OF THE
SATELLITE POSITIONS. ISABEL REMAINS A POWERFUL HURRICANE BASED ON A
SATELLITE INTENSITY ESTIMATE OF 115 KT FROM ALL THREE AGENCIES.
OUTFLOW ALSO REMAINS VERY IMPRESSIVE AND HAS IMPROVED TO THE WEST
AND TO THE EAST...WHILE BECOMING SLIGHTLY RESTRICTED TO THE NORTH.

THE INITIAL MOTION ESTIMATE IS 280/10. THERE MAY BE SOME WOBBLE IN
THE TRACK OVER THE PAST 6 HOUR... WHICH IS FAIRLY TYPICAL OF
INTENSE HURRICANES. RECENT SATELLITE FIX POSITIONS SUGGEST A SHARP
DUE WEST MOTION OF 270 DEGREES. HOWEVER...I WOULD PREFER TO WAIT
UNTIL THE EYE BECOMES MORE DISTINCT BEFORE TAKING ISABEL OFF ON A
DUE WESTWARD TRACK. OTHER THAN THAT...THERE IS NO SIGNIFICANT
CHANGE TO THE PREVIOUS FORECAST TRACK OR REASONING. THE 06Z GFS AND
NOGAPS MODELS HAVE FINALLY ABANDONED THEIR SLIGHT SOUTHWARD JOG AND
ACTUALLY LOOK QUITE REASONABLE. THE GFDL AND UKMET MODELS...HOWEVER
...HAVE MORE POLEWARD MOTION...AND THE UKMET NOW APPEARS TO HAVE
DEVELOPED A RIGHT-OF-TRACK BIAS. THEREFORE...THE GFS AND NOGAPS
SOLUTIONS WERE FOLLOWED FOR THIS ADVISORY...WHICH SEEMS CONSISTENT
WITH THE CURRENT 5-WAVE MID-LATITUDE LONGWAVE PATTERN OVER THE
NORTHERN HEMISPHERE. THE STRONGEST ANCHOR LOW/TROUGH IS LOCATED
OVER SOUTHERN GREENLAND AND EXTENDS SOUTHWARD ALONG 45W LONGITUDE.
MAINTAINING A 5-WAVE PATTERN SPACING WOULD EVENTUALLY YIELD A
LONGWAVE TROUGH OVER THE CENTRAL U.S. IN 3-5 DAYS...WITH A RIDGE
ALONG AND EAST OF THE U.S. EAST COAST...AS DEPICTED BY THE GFS.

THE OUTFLOW ON THE WEST SIDE OF ISABEL IS EXPANDING WESTWARD AND IS
STARTING TO GET DRAWN INTO THE LARGE MID-/UPPER-LOW NORTH OF PUERTO
RICO. OUTFLOW TO THE EAST IS ALSO EXPANDING...SO SOME ADDITIONAL
STRENGTHENING IS POSSIBLE AT ANY TIME. HOWEVER...TIMING THE EFFECTS
OF INNER-CORE CONVECTIVE CHANGES IS IMPOSSIBLE MORE THAN ABOUT 12
HOURS IN ADVANCE...SO THE INTENSITY FORECAST SHOWS LITTLE CHANGE.

FORECASTER STEWART

FORECAST POSITIONS AND MAX WINDS

INITIAL 10/1500Z 21.3N 50.9W 115 KT
12HR VT 11/0000Z 21.5N 52.4W 115 KT
24HR VT 11/1200Z 21.7N 54.4W 115 KT
36HR VT 12/0000Z 21.8N 56.0W 115 KT
48HR VT 12/1200Z 21.9N 57.8W 115 KT
72HR VT 13/1200Z 22.0N 61.0W 115 KT
96HR VT 14/1200Z 23.0N 64.5W 110 KT
120HR VT 15/1200Z 23.5N 68.0W 110 KT

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ZCZC MIATCDAT3 ALL
TTAA00 KNHC DDHHMM
HURRICANE ISABEL DISCUSSION NUMBER 19
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
5 PM EDT WED SEP 10 2003

SATELLITE IMAGERY INDICATES ISABEL HAS STRENGTHENED THIS AFTERNOON
AS EYEWALL CLOUD TOPS HAVE COOLED TO -75C AND COLDER...WHILE THE EYE
HAS CLEARED OUT AND WARMED SIGNIFICANTLY. OBJECTIVE DVORAK
T-NUMBERS OVER THE PAST 2 HOURS AVERAGE OUT TO T6.5...OR 127 KT...
WITH A PEAK T-NUMBER OF 7.1...OR 143 KT...AT 1815Z. THE 3-HOUR ODT
AVERAGE IS T6.3...OR 122 KT. THESE INTENSITY ESTIMATES EASILY
JUSTIFY INCREASING THE INTENSITY TO 120 KT FOR THIS ADVISORY. IT IS
QUITE POSSIBLE THAT ISABEL IS A LITTLE STRONGER THAN THE ADVISORY
INTENSITY INDICATES...BUT WE PREFER TO USE THE 3-HOUR ODT VALUES TO
SMOOTH OUT ANY INTENSITY FLUCTUATIONS.

THE INITIAL MOTION ESTIMATE IS 275/10. THERE REMAINS NO SIGNIFICANT
CHANGE TO THE PREVIOUS FORECAST TRACKS OR REASONINGS. ISABEL HAS
DEFINITELY MADE THE TURN TOWARD THE WEST. UNFORTUNATELY...THE 12Z
GFS MODEL HAS RETURNED TO ITS OLD WAYS AND NOW MAKES A JOG BACK TO
THE WEST-SOUTHWEST ALONG 20N LATITUDE IN 36-48 HOURS. THIS APPEARS
TO BE DUE TO POOR INITIALIZATION OF ISABEL BY THE MODEL...AND THE
GFS MAINTAINS A PATHETIC LOOKING LOW- TO MID-LEVEL CIRCULATION...
CERTAINLY NOTHING REMOTELY RESEMBLING A MAJOR HURRICANE...THROUGH
72 HOURS. THE RESULT IS THAT WEAK MID-LEVEL RIDGING TO THE WEST OF
ISABEL FORCES THE CYCLONE WEST-SOUTHWESTWARD. THE CANADIAN MODEL
AND THE UKMET... TO A SLIGHTLY LESSER DEGREE...ALSO HAVE SIMILAR
LOOKING WEAK CIRCULATIONS...THROUGH THE SAME TIME PERIOD. ONLY THE
12Z NOGAPS MODEL INITIALIZES ISABEL AS A SIGNIFICANT TROPICAL
CYCLONE. SINCE THE NOGAPS MODEL IS VERY CLOSE TO THE PREVIOUS
FORECAST TRACK...LITTLE CHANGE WAS MADE TO THE PREVIOUS TRACK
....WHICH IS A LITTLE SOUTH OF THE NHC MODEL CONSENSUS AND CLOSE TO
THE NOGAPS AND GFDL SOLUTIONS.

THE OUTFLOW ON THE WEST SIDE OF ISABEL CONTINUES TO EXPAND WESTWARD
AS IS GETS DRAWN INTO THE LARGE MID-/UPPER-LOW NORTH OF HISPANIOLA.
THE CYCLONE WILL CONTINUE TO MOVE OVER WARMER WATER AND REMAIN IN A
FAVORABLE UPPER-LEVEL OUTFLOW PATTERN...SO SOME ADDITIONAL SLIGHT
STRENGTHENING IS STILL POSSIBLE AT ANY TIME. HOWEVER...THE ONLY GOOD
NEWS ABOUT INTENSE HURRICANES IS THAT THEY GENERALLY DO NOT REMAIN
INTENSE FOR VERY LONG...SO SOME SLIGHT WEAKENING IS FORECAST.

FORECASTER STEWART

FORECAST POSITIONS AND MAX WINDS

INITIAL 10/2100Z 21.2N 51.9W 120 KT
12HR VT 11/0600Z 21.3N 53.5W 125 KT
24HR VT 11/1800Z 21.4N 55.2W 120 KT
36HR VT 12/0600Z 21.5N 56.9W 120 KT
48HR VT 12/1800Z 21.7N 58.6W 120 KT
72HR VT 13/1800Z 22.0N 62.5W 115 KT
96HR VT 14/1800Z 23.0N 66.0W 115 KT
120HR VT 15/1800Z 23.5N 69.5W 115 KT
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HURRICANE ISABEL DISCUSSION NUMBER 20
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
11 PM EDT WED SEP 10 2003

SATELLITE INTENSITY ESTIMATES ARE A CONSENSUS T6.5...127 KT...AND SO
THE ADVISORY INTENSITY IS INCREASED TO 125 KT. THE MOST RECENT 3-HR
AVERAGE OBJECTIVE DVORAK INTENSITY ESTIMATE WAS JUST BELOW 130 KT.
ALTHOUGH THERE IS CURRENTLY NO UPPER-LEVEL OUTFLOW TO THE NORTH...
THERE ARE TWO VERY EFFICIENT OUTFLOW CHANNELS OPERATING TO THE WEST
AND EAST OF THE HURRICANE. ISABEL IS EXPECTED TO REMAIN A MAJOR
HURRICANE THROUGHOUT THE FORECAST PERIOD. WIND RADII HAVE BEEN
ADJUSTED SLIGHTLY INWARD BASED ON A RECENT QUIKSCAT PASS.

THE INITIAL MOTION ESTIMATE IS 270/9. THE WESTWARD TRACK IS THE
RESULT OF A MID TO UPPER-LEVEL HIGH CURRENTLY LOCATED NORTH OF
ISABEL NEAR 30N. THIS HIGH IS FORECAST BY GLOBAL MODELS TO SLIDE
WESTWARD WITH ISABEL FOR THE NEXT TWO TO THREE DAYS...AND MAINTAIN
ISABEL ON A TRACK JUST A BIT NORTH OF DUE WESTWARD. BY DAYS 4 AND
5 OF THE FORECAST PERIOD...NEARLY ALL OF THE GLOBAL MODEL GUIDANCE
SLOWS THE WESTWARD PROGRESSION OF THE HIGH AND ALLOWS THE TRACK TO
SLOW AND BEND SLIGHTLY TO THE RIGHT. THE FOUR MAIN TRACK MODELS...
THE GFDL...GFS...UKMET...AND NOGAPS...ARE NOW IN VERY GOOD
AGREEMENT THROUGH DAY 5...AS THE GFS HAS SHIFTED SUBSTANTIALLY
NORTHWARD FROM ITS PREVIOUS RUN. THE OFFICIAL FORECAST HAS BEEN
ADJUSTED NORTHWARD TO BE IN BETTER AGREEMENT WITH THE CURRENT
GUIDANCE...BUT IS STILL ON THE SOUTH EDGE OF THE GUIDANCE ENVELOPE.
THE ONE OUTLIER IS THE ECMWF...A MODEL VERY SKILLED AT FORECASTING
LARGE-SCALE ATMOSPHERIC PATTERNS...WHICH IS SUBSTANTIALLY SOUTH OF
THE OTHERS IN BRINGING ISABEL NEAR THE EXTREME SOUTHEASTERN BAHAMAS
BY DAY 5.

IT IS NATURAL TO WANT TO SPECULATE ON THE FORECAST TRACK BEYOND 5
DAYS...BUT IT SIMPLY IS NOT POSSIBLE TO DO SO WITH CONFIDENCE. THE
GLOBAL MODELS BEGIN TO DIVERGE MARKEDLY ON HOW MUCH RIDGING WILL
REMAIN OFF THE U.S. SOUTHEAST COAST BY DAY 5. THE EXTENT AND
ORIENTATION OF THIS RIDGING WILL BE CRUCIAL IN DETERMINING THE
POTENTIAL IMPACTS TO THE BAHAMAS AND THE EASTERN UNITED STATES.
GIVEN THAT ISABEL IS STILL SEVERAL DAYS AWAY FROM THESE
AREAS...THIS WOULD BE A GOOD TIME FOR RESIDENTS TO REVIEW THEIR
PREPAREDNESS PLANS IN CASE ISABEL BECOMES A DIRECT THREAT.

THE FIRST RECONNAISSANCE AIRCRAFT FLIGHT INTO ISABEL IS SCHEDULED
FOR FRIDAY AFTERNOON. MISSIONS TO SAMPLE THE SYNOPTIC ENVIRONMENT
OF ISABEL ARE ALSO SCHEDULED TO BEGIN ON FRIDAY.

FORECASTER FRANKLIN

FORECAST POSITIONS AND MAX WINDS

INITIAL 11/0300Z 21.1N 52.8W 125 KT
12HR VT 11/1200Z 21.2N 54.3W 125 KT
24HR VT 12/0000Z 21.4N 56.2W 125 KT
36HR VT 12/1200Z 21.7N 58.0W 120 KT
48HR VT 13/0000Z 22.0N 60.0W 120 KT
72HR VT 14/0000Z 23.0N 64.0W 115 KT
96HR VT 15/0000Z 24.0N 68.0W 115 KT
120HR VT 16/0000Z 25.0N 71.5W 115 KT

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HURRICANE ISABEL DISCUSSION NUMBER 21
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
5 AM EDT THU SEP 11 2003

...CORRECTION FOR EASTERLY FLOW INSTEAD OF WESTERLY FLOW

THE CLOUD PATTERN IS EXCELLENT WITH A DISTINCT EYE SURROUNDED BY
VERY DEEP CONVECTION. WATER VAPOR IMAGES SHOW THAT ISABEL CONTINUES
TO HAVE TWO WELL-ESTABLISHED AND IMPRESSIVE OUTFLOW CHANNELS.
INITIAL INTENSITY REMAINS AT 125 KNOTS AND BECAUSE THE SHEAR IS LOW
AND THE OCEAN IS WARM...ISABEL WILL LIKELY REMAIN A MAJOR HURRICANE
THROUGH 5 DAYS.

ISABEL IS MOVING WESTWARD ABOUT 9 KNOTS EMBEDDED WITHIN A DEEP LAYER
EASTERLY FLOW SOUTH OF A HIGH PRESSURE RIDGE. THIS RIDGE IS
FORECAST TO PERSIST FORCING ISABEL TO MOVE ON A GENERAL WESTWARD
TRACK. BECAUSE THE RIDGE SHOULD BEGIN TO TEMPORARELY
WEAKEN...ISABEL COULD TURN MORE TO THE WEST-NORTHWEST IN ABOUT 24
TO 36 HOURS. GLOBAL MODELS ARE CLUSTERED AND THEY ALL SUGGEST A
WEST-NORTHWEST TURN...BRINGING THE CORE OF ISABEL PARALLEL AND JUST
TO THE NORTH OF THE BAHAMAS. IN FACT THE GFS...NO LONGER BRINGS
ISABEL STRAIGHT WESTWARD AS IN PREVIOUS RUNS AND THE GFDL...WHICH
HAS BEEN PERFORMING QUITE WELL SO FAR...HAS SHIFTED THE TRACK
SLIGHTLY NORTHWARD.

NOTE: ALL MODELS RE-DEVELOP A RIDGE OVER THE WESTERN ATLANTIC JUST
OFF THE U.S. EAST COAST IN ABOUT 5 DAYS. THE STRENGTH AND LOCATION
OF THIS RIDGE WILL BE CRITICAL IN DETERMINING HOW CLOSE ISABEL WILL
GET TO THE UNITED STATES EAST COAST.

FORECASTER AVILA

FORECAST POSITIONS AND MAX WINDS

INITIAL 11/0900Z 21.3N 53.7W 125 KT
12HR VT 11/1800Z 21.4N 55.1W 125 KT
24HR VT 12/0600Z 21.7N 57.0W 125 KT
36HR VT 12/1800Z 22.0N 59.0W 120 KT
48HR VT 13/0600Z 22.5N 61.0W 120 KT
72HR VT 14/0600Z 24.0N 65.0W 115 KT
96HR VT 15/0600Z 25.0N 69.0W 115 KT
120HR VT 16/0600Z 26.0N 72.0W 115 KT

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Sciencerocks
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Re: Hurricane Isabel

#8 Postby Sciencerocks » Sat May 20, 2023 6:55 pm

ZCZC MIATCDAT3 ALL
TTAA00 KNHC DDHHMM
HURRICANE ISABEL DISCUSSION NUMBER 22
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
11 AM EDT THU SEP 11 2003

ISABEL IS MORE SYMMETRICAL-LOOKING THAN IT WAS YESTERDAY...AND IT
HAS A TEXTBOOK APPEARANCE ON VISIBLE AND INFRARED SATELLITE IMAGES.
THE WELL-DEFINED 25 N MI DIAMETER EYE IS EMBEDDED IN VERY DEEP
CONVECTION. DVORAK T-NUMBERS AVERAGE ABOUT 6.7 GIVING A CURRENT
INTENSITY ESTIMATE OF 130 KT. THERE ARE NO OBVIOUS IMPEDIMENTS IN
THE ENVIRONMENT...SO CHANGES IN STRENGTH ARE LIKELY TO BE DICTATED
PRIMARILY BY INNER-CORE PROCESSES. ISABEL SHOULD REMAIN A MAJOR
HURRICANE THROUGH THE FORECAST PERIOD.

THE HURRICANE IS MOVING WEST NEAR 8 KT AS IT REMAINS EMBEDDED IN
DEEP LAYER EASTERLIES TO THE SOUTH OF A HIGH PRESSURE SYSTEM.
GLOBAL AND GFDL MODEL GUIDANCE INDICATE A GRADUAL TURN TOWARD THE
WEST-NORTHWEST OVER THE NEXT FEW DAYS AS ISABEL NEARS THE WESTERN
SIDE OF THE HIGH. THIS IS ALSO SHOWN IN THE OFFICIAL TRACK
FORECAST...WHICH IS QUITE CLOSE TO THE PREVIOUS ONE. THE NHC TRACK
IS ALSO FAIRLY CLOSE TO THE GUNA CONSENSUS AND TO THE FSU
SUPERENSEMBLE TRACK. THE LATEST GFDL RUN IS A LITTLE NORTHEAST OF
THE OFFICIAL TRACK...AND THAT MODEL HAS BEEN TRENDING MORE AND MORE
TO THE RIGHT IN THE LAST FEW RUNS.

LATE IN THE FORECAST PERIOD...THE TWO MOST IMPORTANT PLAYERS IN THE
STEERING OF ISABEL APPEAR TO BE THE RIDGE NEAR THE U.S. EAST COAST
AND A MID-LATITUDE TROUGH OVER THE EAST-CENTRAL UNITED STATES.
THERE IS SOME DIFFERENCE IN THE WAY THE DYNAMICAL GUIDANCE HANDLES
THESE FEATURES. SOME OF THE MODELS...SUCH AS THE GFS...NOW SHOW
THE TROUGH AS THE MORE DOMINANT SYSTEM. IF THIS TURNS OUT TO BE
THE CASE...THEN THE HURRICANE COULD TURN MORE NORTHWARD THAN SHOWN
HERE.

FORECASTER PASCH

FORECAST POSITIONS AND MAX WINDS

INITIAL 11/1500Z 21.4N 54.5W 130 KT
12HR VT 12/0000Z 21.5N 56.0W 130 KT
24HR VT 12/1200Z 21.8N 58.0W 130 KT
36HR VT 13/0000Z 22.2N 60.0W 125 KT
48HR VT 13/1200Z 22.8N 61.9W 120 KT
72HR VT 14/1200Z 24.0N 65.5W 115 KT
96HR VT 15/1200Z 25.0N 69.0W 115 KT
120HR VT 16/1200Z 26.5N 72.0W 115 KT

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HURRICANE ISABEL DISCUSSION NUMBER 23
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
5 PM EDT THU SEP 11 2003

ISABEL HAS CONTINUED TO INTENSIFY TODAY. DVORAK T-NUMBERS FROM ALL
3 AGENCIES...TAFB...SAB...AND AFWA ARE NOW 7.0 AND OBJECTIVE
T-NUMBERS ARE ALSO ABOUT THE SAME VALUE. THIS SUPPORTS A CURRENT
INTENSITY ESTIMATE OF 140 KT...A CATEGORY 5 ON THE SAFFIR-SIMPSON
HURRICANE SCALE. HURRICANES RARELY MAINTAIN SUCH STRENGTH FOR VERY
LONG...AND ISABEL MAY NOT STAY A CAT 5 FOR EVEN AS LONG AS SHOWN
HERE. THERE IS AN UPPER-LEVEL CYCLONE ABOUT 15 DEGREES TO THE
WEST-NORTHWEST OF THE HURRICANE BUT THIS SYSTEM APPEARS TO BE
NARROWING AND IF THIS TREND CONTINUES...IT SHOULD NOT HAVE MUCH OF
AN IMPACT ON THE INTENSITY OF ISABEL. ANOTHER POSSIBLE FACTOR IS
THE COOLED SST WAKE PRODUCED BY HURRICANE FABIAN IN THE VICINITY OF
63W. SINCE THERE DO NOT TO BE ANY MAJOR INHIBITING FACTORS IN THE
ENVIRONMENT...INTERNAL DYNAMICS SUCH AS EYEWALL REPLACEMENT CYCLES
WILL PROBABLY HAVE THE GREATEST INFLUENCE ON INTENSITY CHANGE. THE
OFFICIAL FORECAST ASSUMES THAT WE WILL CONTINUE TO HAVE A MAJOR
HURRICANE ON OUR HANDS THROUGHOUT THE FORECAST PERIOD.

MOTION CONTINUES AT ABOUT 280/8...ALONG WITH SOME MINOR TROCHOIDAL
WOBBLES. A DEEP-LAYER HIGH PRESSURE AREA TO THE NORTH OF ISABEL IS
LIKELY TO MAINTAIN THE SLOW WESTWARD TO WEST-NORTHWESTWARD STEERING
OVER THE NEXT SEVERAL DAYS. THE CURRENT NHC FORECAST IS SOMEWHAT
SLOWER THAN THE PREVIOUS ONE...BUT FASTER THAN THE GUNA CONSENSUS.
THIS IS FAIRLY CLOSE TO THE LATEST U.K. MET OFFICE TRACK. THE
LATTER MODEL IS THE WESTERNMOST OF THE GUIDANCE SUITE.

THE BIG QUESTION CONTINUES TO BE WHAT WILL HAPPEN BEYOND THE 5-DAY
FORECAST PERIOD. IT IS STILL IMPOSSIBLE TO STATE WITH ANY
CONFIDENCE WHETHER A SPECIFIC AREA ALONG THE U.S. COAST WILL BE
IMPACTED BY ISABEL. THIS WILL LIKELY DEPEND ON THE RELATIVE
STRENGTH AND POSITIONING OF A MID-TROPOSPHERIC RIDGE NEAR THE EAST
COAST AND A MID-LATITUDE TROUGH TO THE WEST OR NORTHWEST AROUND THE
MIDDLE OF NEXT WEEK. UNFORTUNATELY...WE HAVE LITTLE SKILL IN
PREDICTING THE EVOLUTION OF STEERING FEATURES AT THESE LONG RANGES.

FORECASTER PASCH

FORECAST POSITIONS AND MAX WINDS

INITIAL 11/2100Z 21.6N 55.3W 140 KT
12HR VT 12/0600Z 21.7N 56.7W 140 KT
24HR VT 12/1800Z 21.9N 58.6W 135 KT
36HR VT 13/0600Z 22.4N 60.5W 130 KT
48HR VT 13/1800Z 22.9N 62.3W 125 KT
72HR VT 14/1800Z 24.0N 65.5W 115 KT
96HR VT 15/1800Z 25.0N 68.5W 115 KT
120HR VT 16/1800Z 26.0N 71.5W 115 KT

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HURRICANE ISABEL DISCUSSION NUMBER 24
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
11 PM EDT THU SEP 11 2003

ISABEL LOOKS LIKE IT IS ABOUT TO BEGIN AN EYEWALL REPLACEMENT CYCLE.
AN AMSU MICROWAVE PASS AT 1737Z SHOWED THREE-FOURTHS OF AN OUTER
EYEWALL. AT 2313Z...AN SSMI PASS SHOWED TWO CONCENTRIC
EYEWALLS...WITH SOME EROSION ON THE NORTH SIDE OF THE INNER
EYEWALL. THIS IS CONSISTENT WITH CONVENTIONAL IR IMAGERY WHICH
ALSO SHOWS CONSIDERABLE WARMING OF THE CONVECTION IN THE NORTH
EYEWALL OVER THE PAST SEVERAL HOURS. THE RELATIVELY LIGHT WIND EYE
AND MOAT BETWEEN THE TWO EYEWALLS CAN EVEN BE SEEN IN THE RAW
RETURNED SIGNAL FROM THE QUIKSCAT SCATTEROMETER PASS AT 2116Z.
WHAT THIS MOST LIKELY MEANS IS THAT THE HURRICANE WILL WEAKEN OVER
THE NEXT 12 HOURS OR SO AS THE INNER EYEWALL COLLAPSES...BUT THEN
COULD REINTENSIFY AFTER THAT AS THE OUTER EYEWALL CONTRACTS. WE DO
NOT NORMALLY TRY TO INCLUDE THESE KINDS OF FLUCTUATIONS IN THE
OFFICIAL INTENSITY FORECAST...BUT BECAUSE THIS REPLACEMENT SEEMS TO
BE UNDERWAY I HAVE TAKEN A SHOT AT IT. REGARDLESS OF HOW THE CORE
STRUCTURE EVOLVES IN THE NEAR TERM...ISABEL IS EXPECTED TO REMAIN A
MAJOR HURRICANE THROUGHOUT THE FORECAST PERIOD. RECENT SST
ANALYSES SHOW THAT THE COOL WAKE OF FABIAN IS GRADUALLY DIMINISHING
AND MAY NOT HAVE A SIGNIFICANT EFFECT ON ISABEL.

A SLIGHT WOBBLE TO THE LEFT IS OCCURRING AT THE MOMENT...BUT THE
LONG-TERM MOTION REMAINS 280/8. THERE HAS BEEN NO SIGNIFICANT
CHANGE TO THE SYNOPTIC THINKING...SHORT-RANGE MODEL GUIDANCE...OR
OFFICIAL TRACK FORECAST. A DEEP-LAYER HIGH PRESSURE AREA TO THE
NORTH OF ISABEL IS LIKELY TO MAINTAIN THE SLOW WESTWARD TO
WEST-NORTHWESTWARD STEERING OVER THE NEXT SEVERAL DAYS. BEYOND THE
5-DAY FORECAST PERIOD...MODEL GUIDANCE BEGINS TO DIVERGE AS
STEERING CURRENTS WEAKEN. IT IS STILL TOO EARLY TO SPECULATE WHAT
PORTIONS OF THE U.S. EAST COAST MIGHT BE AFFECTED BY ISABEL.

FORECASTER FRANKLIN

FORECAST POSITIONS AND MAX WINDS

INITIAL 12/0300Z 21.6N 56.1W 140 KT
12HR VT 12/1200Z 21.9N 57.5W 130 KT
24HR VT 13/0000Z 22.3N 59.4W 135 KT
36HR VT 13/1200Z 22.7N 61.3W 130 KT
48HR VT 14/0000Z 23.3N 63.2W 125 KT
72HR VT 15/0000Z 24.5N 66.5W 115 KT
96HR VT 16/0000Z 25.5N 69.5W 115 KT
120HR VT 17/0000Z 26.5N 72.5W 110 KT

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HURRICANE ISABEL DISCUSSION NUMBER 25
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
5 AM EDT FRI SEP 12 2003

THERE ARE NO NEW CHANGES TO REPORT OR THAT CAN BE ADDED TO THE
STRUCTURE AND INTENSITY OF ISABEL AFTER THE PREVIOUS DISCUSSION.
BASED ON THE OUSTANDING CLOUD PATTERN...SATELLITE INTENSITY
ESTIMATES STILL SUPPORT 140 KNOTS. REGARDLESS OF HOW THE CORE
STRUCTURE EVOLVES IN THE NEAR TERM...ISABEL IS EXPECTED TO REMAIN A
MAJOR HURRICANE THROUGHOUT THE FORECAST PERIOD.

HERE COMES A LITTLE DISCUSSION ABOUT THE FOUR MAIN MODELS. THE GFDL
WHICH HAS BEEN PERFORMING QUITE WELL...TURNS THE HURRICANE MORE TO
THE NORTHWEST AND NORTH-NORTHWEST...AND DEPENDING UPON THE RUN YOU
PICK...THE TURN OCCURS FARTHER TO THE WEST OR FARTHER TO THE EAST.
ON THE OTHER HAND...THE UK MODEL WHICH HAS HAS BEEN MORE CONSISTENT
...MOVES THE HURRICANE FASTER AND BRING ISABEL DANGEROUSLY CLOSE TO
THE U.S. COAST IN 5 DAYS. THE GFS WHICH HAS BEEN CHANGING ITS TUNE
FROM RUN TO RUN...IS MUCH SLOWER AND IN 5 DAYS PLACES THE HURRICANE
ABOUT 450 N MI FROM THE U.S COAST. THE GFS EVENTUALLY BRINGS THE
CENTER NEAR THE COAST OF NORTH CAROLINA IN SEVERAL MORE DAYS.
FINALLY...THE NOGAPS IS VERY SIMILAR TO THE GFS UP TO 5 DAYS.

NOTE: THEY ALL HAVE IN COMMON THE DEVELOPMENT AND THE WESTWARD
EXPANSION OF A STRONG RIDGE TO THE NORTH OF THE HURRICANE BEYOND 5
DAYS. IF THIS PATTERN EVOLVES...THE HURRICANE COULD POSE A
SIGNIFICANT THREAT TO THE U.S. EAST COAST.

HAVING SAID ALL THAT...HERE COMES THE OFFICIAL FORECAST. ISABEL HAS
BEEN MOVING TOWARD THE WEST OR 270 DEGREES AT 8 KNOTS AROUND A
DEEP-LAYER SUBTROPICAL HIGH. THIS PATTERN WOULD FAVOR A WEST TO
WEST-NORTHWEST TRACK THROUGH 5 DAYS WITH NO SIGNIFICANT CHANGE IN
FORWARD SPEED. MOST IMPORTANTLY...DUE TO THE LARGE VARIATION IN
MODELS FROM RUN TO RUN...IT IS TOO EARLY TO SPECULATE WHAT PORTIONS
OF THE U.S. EAST COAST MIGHT BE AFFECTED BY ISABEL.

FORECASTER AVILA

FORECAST POSITIONS AND MAX WINDS

INITIAL 12/0900Z 21.7N 57.0W 140 KT
12HR VT 12/1800Z 22.0N 58.4W 130 KT
24HR VT 13/0600Z 22.5N 60.5W 135 KT
36HR VT 13/1800Z 23.0N 62.5W 130 KT
48HR VT 14/0600Z 23.5N 64.5W 125 KT
72HR VT 15/0600Z 25.0N 69.0W 115 KT
96HR VT 16/0600Z 26.0N 71.5W 115 KT
120HR VT 17/0600Z 27.5N 74.0W 110 KT

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HURRICANE ISABEL DISCUSSION NUMBER 26
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
11 AM EDT FRI SEP 12 2003

MORNING SATELLITE IMAGERY AND MICROWAVE DATA FROM LAST NIGHT SHOW
THAT ISABEL HAS COMPLETED A CONCENTRIC EYEWALL CYCLE. IT NOW HAS A
WELL-DEFINED 35 NM WIDE EYE WELL EMBEDDED IN THE CENTRAL DENSE
OVERCAST. THE CIRRUS OUTFLOW IS STILL GOOD IN THE SOUTHEAST AND
NORTHWEST QUADRANTS...BUT IS ONLY FAIR TO POOR ELSEWHERE AND ON THE
WHOLE LOOKS LESS GOOD THAN YESTERDAY. SATELLITE INTENSITY ESTIMATES
ARE ALL 140 KT...SO THAT IS THE INITIAL INTENSITY. HOWEVER...SINCE
THE TIME OF THE ESTIMATES THERE HAS BEEN SOME WARMING OF THE
EYEWALL CONVECTIVE TOPS. NOAA AND AIR FORCE RESERVE HURRICANE
HUNTER AIRCRAFT WILL INVESTIGATE THE HURRICANE THIS AFTERNOON.

THE INITIAL MOTION IS 270/8. ISABEL IS CURRENTLY SOUTH OF A
LOW/MID-LEVEL RIDGE...WITH AN ANTICYCLONE CENTER IN WATER VAPOR
IMAGERY NEAR 29N55W...AND BETWEEN LARGE UPPER-LEVEL TROUGHS ALONG
68W AND 41W. IN THE SHORT TERM...THIS SHOULD PRODUCE A WESTWARD TO
POSSIBLY WEST-NORTHWESTWARD MOTION. FURTHER UPSTREAM...A DEEP
LAYER CYCLONIC CIRCULATION IS OVER THE SOUTHEASTERN UNITED STATES
WITH A MID/UPPER-LEVEL RIDGE BUILDING OVER SOUTHEASTERN CANADA.
THE EVOLUTION OF THESE FEATURES...ALONG WITH THE WESTERLIES OVER
THE CENTRAL UNITED STATES...WILL DETERMINE THE LONG-RANGE COURSE OF
ISABEL. NHC TRACK GUIDANCE GENERALLY AGREES ON A WESTWARD TO
WEST-NORTHWESTWARD MOTION THROUGH 72 HR...AND THE OFFICIAL FORECAST
TRACK FOLLOWS ALONG THE SOUTH EDGE OF THE GUIDANCE. CONSIDERABLE
DIVERGENCE OCCURS AFTER 72 HR. THE UKMET CALLS FOR A GRADUAL TURN
TOWARD THE NORTHWEST BY 120 HR TOWARD A WEAKNESS IN RIDGE LEFT BY
THE DEEP-LAYER LOW AS IT LIFTS NORTHWARD. ON THE OTHER HAND...THE
GFS...NOGAPS...GFDL... CANADIAN...AND ECMWF MODELS ALL CALL FOR AN
EARLIER AND MORE NORTHWARD MOTION. SINCE ALL MODELS KEEP SOME DEEP
LAYER RIDGING OVER THE NORTHWEST ATLANTIC NORTH AND NORTHEAST OF
ISABEL...SO SHARP OF A TURN LOOKS A LITTLE DUBIOUS. THUS...THE 3-5
DAY OFFICIAL FORECAST WILL LEAN TOWARD THE UKMET AT A SLOWER
FORWARD SPEED.

ISABEL IS FORECAST TO REMAIN IN A WARM-WATER LOW-SHEAR ENVIRONMENT
FOR ROUGHLY THE NEXT 72 HR. DURING THAT TIME...THE INTENSITY
SHOULD BE CONTROLLED MAINLY BY HARD-TO-FORECAST EYEWALL REPLACEMENT
CYCLES. THE INTENSITY FORECAST WILL THUS CALL FOR A SLOW WEAKENING
THROUGH THAT TIME BASED ON CONTINUITY FROM THE PREVIOUS FORECASTS
AND CLIMATOLOGY. AFTER 72 HR...THE GFS AND NOGAPS SUGGEST THAT
ISABEL MAY MOVE NORTH OF A 200 MB ANTICYCLONE AND GET EXPOSED TO
SOME SHEAR. THE SHIPS MODEL RESPONDS TO THIS BY FORECASTING 30 KT
OF SOUTHWESTERLY SHEAR BY 120 HR. BASED ON THIS...THE INTENSITY
FORECAST WILL CALL FOR A SOMEWHAT FASTER WEAKENING. IT SHOULD BE
NOTED THAT THE LARGE-SCALE MODELS ALL FORECAST ISABEL TO GROW IN
SIZE BEYOND 72 HR...WHICH MAY BE REFLECTED IN LATER WIND RADII
FORECASTS.

GIVEN THE DIVERGENCE OF THE MODELS AT 120 HR...IT IS STILL TO EARLY
TO EVEN SPECULATE WHICH PARTS...IF ANY...OF EASTERN COAST OF THE
UNITED STATES MAY GET AFFECTED BY ISABEL.

FORECASTER BEVEN

FORECAST POSITIONS AND MAX WINDS

INITIAL 12/1500Z 21.6N 57.8W 140 KT
12HR VT 13/0000Z 21.8N 59.1W 135 KT
24HR VT 13/1200Z 22.2N 61.2W 135 KT
36HR VT 14/0000Z 22.8N 63.4W 135 KT
48HR VT 14/1200Z 23.4N 65.5W 130 KT
72HR VT 15/1200Z 24.5N 69.5W 125 KT
96HR VT 16/1200Z 25.5N 72.0W 110 KT
120HR VT 17/1200Z 27.5N 75.0W 105 KT

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HURRICANE ISABEL DISCUSSION NUMBER 27
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
5 PM EDT FRI SEP 12 2003

REPORTS FROM AIR FORCE RESERVE AND NOAA HURRICANE HUNTER AIRCRAFT
CONFIRM THAT ISABEL IS A CATEGORY 5 HURRICANE. MAXIMUM OBSERVED
FLIGHT-LEVEL WINDS SO FAR ARE 156 KT AT 700 MB...SUPPORTING SURFACE
WINDS NEAR 140 KT. THE EYE IS 30 NM WIDE WITH A CLOSED WALL AND A
MINIMUM PRESSURE OF 920 MB. THE INITIAL INTENSITY THUS REMAINS 140
KT...WHICH AGREES WITH SATELLITE INTENSITY ESTIMATES. IT SHOULD BE
NOTED THAT ISABEL LOOKS A LITTLE LESS ORGANIZED IN SATELLITE
IMAGERY THAN IT DID 24 HR AGO. THUS IT MIGHT HAVE BEEN A LITTLE
STRONGER YESTERDAY.

THE EYE HAS RECENTLY NUDGED TO THE RIGHT...BUT THE LONGER TERM
MOTION REMAINS 270/8. THERE IS LITTLE CHANGE IN THE SYNOPTIC
PATTERN OR REASONING FROM THE PREVIOUS FORECAST. ISABEL IS
CURRENTLY SOUTH OF A DEEP LAYER RIDGE...WITH AN ANTICYCLONE SEEN
IN WATER VAPOR IMAGERY NEAR 29N55W...AND UPPER-LEVEL TROUGHS ALONG
68W AND 42W. IN THE SHORT TERM...THIS SHOULD PRODUCE A WESTWARD TO
POSSIBLY WEST-NORTHWESTWARD MOTION. UPSTREAM...A DEEP LAYER
CYCLONIC CIRCULATION IS OVER THE SOUTHEASTERN UNITED
STATES WITH A MID/UPPER-LEVEL RIDGE BUILDING OVER SOUTHEASTERN
CANADA. LARGE-SCALE GUIDANCE FORECASTS THE SOUTHEASTERN SYSTEM TO
MOVE NORTHWARD...LEAVING A WEAKNESS ON THE SOUTHWEST SIDE OF THE
CANADIAN RIDGE AS IT BUILDS EASTWARD INTO THE ATLANTIC. NHC TRACK
GUIDANCE AGREES ON A WESTWARD TO WEST-NORTHWESTWARD MOTION THROUGH
72 HR... AND TO THAT TIME THE FORECAST TRACK IS AN UPDATE OF THE
PREVIOUS PACKAGE. CONSIDERABLE DIVERGENCE OCCURS AFTER 72 HR. THE
UKMET CALLS FOR A GRADUAL TURN TOWARD THE NORTHWEST BY 120 HR IN
RESPONSE TO THE WEAKNESS. THE GFS...NOGAPS...GFDL...AND CANADIAN
MODELS ALL CALL FOR A MORE NORTHWARD MOTION. SINCE ALL MODELS KEEP
SOME DEEP LAYER RIDGING OVER THE NORTHWEST ATLANTIC NORTH AND
NORTHEAST OF ISABEL...SO SHARP OF A TURN CONTINUES TO LOOK A LITTLE
DUBIOUS. THUS...THE 3-5 DAY OFFICIAL FORECAST WILL LEAN TOWARD THE
UKMET. IT SHOULD BE NOTED THAT THE UKMET IS CALLING FOR MORE
NORTHWARD MOTION AFTER 96 HR THAN FORECAST EARLIER...AND THE
OFFICIAL FORECAST IS THUS SHIFTED TO THE RIGHT OF THE PREVIOUS
FORECAST AFTER 72 HR. GIVEN THE DIVERGENCE OF THE MODELS AT 120
HR...IT IS STILL TOO EARLY TO SPECULATE WHICH PARTS...IF ANY...OF
EASTERN COAST OF THE UNITED STATES MAY GET AFFECTED BY ISABEL.

ISABEL IS FORECAST TO REMAIN IN A WARM-WATER LOW-SHEAR ENVIRONMENT
FOR ROUGHLY THE NEXT 72 HR. DURING THAT TIME...THE INTENSITY
SHOULD BE CONTROLLED MAINLY BY EYEWALL REPLACEMENT CYCLES. THE
INTENSITY FORECAST WILL THUS CALL FOR A SLOW WEAKENING THROUGH THAT
TIME BASED ON CONTINUITY FROM PREVIOUS FORECASTS AND CLIMATOLOGY.
AFTER 72 HR...THE GFS AND SHIPS MODELS SUGGEST ISABEL MAY BE
AFFECTED BY SOUTHWESTERLY VERTICAL SHEAR. BASED ON THIS...THE
INTENSITY FORECAST WILL CALL FOR A SOMEWHAT FASTER WEAKENING AFTER
72 HR.

WIND RADII HAVE BEEN REVISED ON THE BASIS OF AIRCRAFT DATA. IT
SHOULD BE NOTED THAT LARGE-SCALE MODELS ALL FORECAST ISABEL TO GROW
IN SIZE BEYOND 72 HR EVEN IF THE INNER CORE WEAKENS.

FORECASTER BEVEN

FORECAST POSITIONS AND MAX WINDS

INITIAL 12/2100Z 21.8N 58.6W 140 KT
12HR VT 13/0600Z 21.9N 59.9W 140 KT
24HR VT 13/1800Z 22.4N 62.1W 135 KT
36HR VT 14/0600Z 23.0N 64.3W 135 KT
48HR VT 14/1800Z 23.6N 66.3W 130 KT
72HR VT 15/1800Z 24.5N 69.5W 125 KT
96HR VT 16/1800Z 26.0N 72.0W 115 KT
120HR VT 17/1800Z 28.5N 75.0W 105 KT

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HURRICANE ISABEL DISCUSSION NUMBER 28
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
11 PM EDT FRI SEP 12 2003

RADAR IMAGES TRANSMITTED FROM A NOAA/HURRICANE RESEARCH DIVISION
FLIGHT INTO ISABEL LATE THIS AFTERNOON SHOWED THE DEVELOPMENT OF A
SECOND CONCENTRIC EYEWALL ABOUT 20 NM OUTSIDE OF THE INNER EYEWALL.
THE AIRCRAFT CREW ALSO REPORTED A STEPPED FREQUENCY MICROWAVE
RADIOMETER MEASUREMENT OF A 140 KT SURFACE WIND LATE IN THE
AFTERNOON. CONCURRENT WITH THIS RE-DEVELOPMENT OF AN OUTER
EYEWALL...THE CORE CONVECTION IS CURRENTLY WEAKENING AS IT DID LAST
NIGHT AT THIS TIME. IN ADDITION...MICROWAVE IMAGERY INDICATES THAT
SOME DRY AIR HAS BEEN INFILTRATING THE CIRCULATION. SUBJECTIVE
DVORAK T-NUMBERS ARE DOWN TO 6.0...AND THE LATEST CIMSS ADVANCED
OBJECTIVE DVORAK 3-HR AVERAGE T NUMBER IS ALSO 6.0...WELL BELOW
CATEGORY FIVE INTENSITY. I VERY MUCH DOUBT THAT ISABEL STILL HAS
WINDS OF 140 KT...BUT SINCE ANOTHER AIRCRAFT WILL BE IN THE
HURRICANE IN JUST THREE HOURS...WE WILL WAIT FOR CONFIRMATION OF
THIS APPARENT WEAKENING TREND. IT IS VIRTUALLY UNHEARD OF FOR A
HURRICANE TO REMAIN AT CATEGORY FIVE STRENGTH FOR MORE THAN 30
HOURS. HOWEVER...ISABEL IS EXPECTED TO REMAIN A MAJOR HURRICANE
THROUGHOUT THE FORECAST PERIOD.

THE INITIAL MOTION IS 275/8. ISABEL REMAINS SOUTH OF A DEEP-LAYER
ANTICYCLONE THAT IS PROVIDING THE WESTWARD STEERING CURRENT. THIS
ANTICYCLONE CONTINUES WESTWARD IN STEP WITH THE HURRICANE...AND
MODEL GUIDANCE IS IN EXCELLENT AGREEMENT ON A WEST TO
WEST-NORTHWEST TRACK FOR THE NEXT 72 HOURS. BY 72 HOURS...THE
EVOLUTION OF A MID- TO UPPER-LEVEL LOW CURRENTLY OVER THE CAROLINAS
COULD PLAY A KEY ROLE IN WHAT PORTION OF THE U.S. EAST COAST WOULD
EVENTUALLY BE AFFECTED BY ISABEL. THE GFS AND NOGAPS MODELS ARE
VERY SIMILAR IN HOLDING THIS FEATURE IN PLACE ALMOST A DAY LONGER
THAN THE UKMET...WITH THE RESULT THAT THE FORMER TWO MODELS TURN
ISABEL MUCH MORE SHARPLY NORTHWARD THAN THE UKMET. THE GFDL TURNS
ISABEL EVEN MORE SHARPLY THAN THE GFS AND NOGAPS MODELS...AND THE
EUROPEAN MODEL ALSO SEEMS TO FAVOR AN EARLIER TURN NORTH. THE
OFFICIAL FORECAST HAS BEEN BEEN SHIFTED TO THE RIGHT OF THE
PREVIOUS ADVISORY TRACK...BUT IS STILL CLOSER TO THE UKMET THAN THE
OTHER GUIDANCE. IN PART THIS IS TO MAINTAIN CONTINUITY WITH
PREVIOUS FORECASTS...BUT ALSO BECAUSE THE UKMET HAS BEEN PRESENTING
A MORE CONSISTENT SOLUTION OVER THE PAST COUPLE OF DAYS THAN HAVE
THE OTHER MODELS.

FORECASTER FRANKLIN

FORECAST POSITIONS AND MAX WINDS

INITIAL 13/0300Z 21.8N 59.5W 140 KT
12HR VT 13/1200Z 22.2N 60.9W 135 KT
24HR VT 14/0000Z 22.8N 63.0W 130 KT
36HR VT 14/1200Z 23.4N 65.1W 130 KT
48HR VT 15/0000Z 24.0N 67.0W 130 KT
72HR VT 16/0000Z 25.0N 70.0W 125 KT
96HR VT 17/0000Z 27.0N 72.5W 115 KT
120HR VT 18/0000Z 29.5N 74.5W 105 KT
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Sciencerocks
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Re: Hurricane Isabel

#9 Postby Sciencerocks » Sat May 20, 2023 6:59 pm

CZC MIATCDAT3 ALL
TTAA00 KNHC DDHHMM
HURRICANE ISABEL DISCUSSION NUMBER 29
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
5 AM EDT SAT SEP 13 2003

THE MUCH ANTICIPATED WEAKENING HAS OCCURRED. DATA FROM A
RECONNAISSANCE PLANE INDICATE THAT THE CENTRAL PRESSURE HAS RISEN
TO 935 MB AND FLIGHT-LEVEL PEAK WINDS ARE 139 KNOTS. INITIAL
INTENSITY HAS BEEN LOWERED TO 130 KNOTS AND THIS IS PROBABLY ON THE
HIGH SIDE. THE RECON ALSO CONFIRMED THE PRESENCE OF TWO CONCENTRIC
EYEWALLS OF 25 AND 35 NMI AND A BAND OF MAXIMUM WINDS ASSOCIATED
WITH EACH EYEWALL...RESPECTIVELY. THERE IS NO SKILL IN PREDICTING IF
THE CURRENT EYEWALL CYCLE WILL RESULT IN FURTHER WEAKENING OR IN
ANOTHER ROUND OF INTENSIFICATION. BEST BET IS TO INDICATE SOME
FLUCTUATIONS IN INTENSITY IN THE NEXT DAY OR TWO WITH A WEAKENING
TREND DUE TO COOLER SSTS OR SHEAR THEREAFTER. NEVERTHERELESS...
ISABEL IS EXPECTED TO REMAIN A MAJOR HURRICANE THROUGHOUT THE
FORECAST PERIOD.

ISABEL IS MOVING TOWARD THE WEST OR 280 DEGREES AT 8 KNOTS AROUND
THE PERIPHERY OF A STRONG DEEP-LAYER ANTICYCLONE. THIS PATTERN IS
EXPECTED TO STEER THE HURRICANE TOWARD THE WEST WITH A GRADUAL TURN
TO THE WEST-NORTHWEST AS INDICATED IN THE OFFICIAL FORECAST. IT
APPEARS THAT THE TROUGH WHICH IS CURRENTLY ERODING THE WESTERN
PORTION OF THE RIDGE WILL WEAKEN AND THE HIGH WILL EXPAND WESTWARD.
THIS EXPANSION OF THE RIDGE WILL CONTROL HOW CLOSE ISABEL
APPROACHES THE U.S EAST COAST.

HIGH UNCERTAINTIES CONTINUE AT LONGER RANGE. THE CONSISTENT AND
GOOD PERFORMER UK MODEL HAS THE HURRICANE NEAR THE COAST OF NORTH
CAROLINA BETWEEN 5 AND 6 DAYS. ON THE OTHER HAND...THE RELIABLE
GFDL TURNS ISABEL NORTHWARD IN FIVE DAYS AT A GOOD DISTANCE AWAY
FROM THE U.S EAST COAST. BECAUSE BOTH MODELS HAVE BEEN VERY GOOD SO
FAR...THE OFFICIAL FORECAST IS IN BETWEEN THESE TWO MODELS. AT THIS
TIME...I WOULD NOT EVEN DISCUSS THE GFS WHICH MOVES THE HURRICANE
EASTWARD FOR THE FIRST 12 TO 18 HOURS IN THE LATEST 00Z RUN AND
ISABEL IS ALREADY WEST OF 60 DEGREES WEST. HOWEVER...THE LARGE
SCALE PATTERN PROVIDED BY THE GFS IS QUITE REASONABLE.

NOTE: THERE ARE NO DYNAMICAL MODELS SUGGESTING THAT ISABEL MIGHT
EVER REACH FLORIDA.

FORECASTER AVILA

FORECAST POSITIONS AND MAX WINDS

INITIAL 13/0900Z 22.0N 60.4W 130 KT
12HR VT 13/1800Z 22.2N 61.6W 130 KT
24HR VT 14/0600Z 23.0N 63.7W 130 KT
36HR VT 14/1800Z 23.5N 65.5W 130 KT
48HR VT 15/0600Z 24.5N 67.5W 130 KT
72HR VT 16/0600Z 26.0N 70.0W 120 KT
96HR VT 17/0600Z 28.5N 72.0W 115 KT
120HR VT 18/0600Z 32.0N 74.5W 105 KT

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HURRICANE ISABEL DISCUSSION NUMBER 30
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
11 AM EDT SAT SEP 13 2003

ISABEL HAS COMPLETED AN EYEWALL REPLACEMENT CYCLE BASED ON A
13/1102Z SSMI OVERPASS SHOWING A CLOSED 35 NMI DIAMETER EYE. THE
INTENSITY IS MAINTAINED AT 130 KT BASED ON CONTINUITY WITH THE
PREVIOUS DATA...A CONSENSUS SATELLITE INTENSITY ESTIMATE OF 127
KT...RAW ODT VALUES OF T6.5...OR 127 KT...AND THE FACT THAT THE EYE
HAS CLEARED OUT NICELY AND SURROUNDING EYEWALL CLOUD TOPS HAVE
COOLED TO -70C AND COLDER ONCE AGAIN. NEXT RECON MISSION IS AT 18Z.

THE INITIAL MOTION IS 280/08. OVER THE PAST 72 HOURS...ISABEL HAS
BEEN MOVING AT 275 DEGREES. THE HURRICANE MADE A SLIGHT NORTHWARD
WOBBLE DURING THE EARLIER EYEWALL REPLACEMENT CYCLE...BUT IT NOW
APPEARS TO HAVE RESUMED A 275-280 DEGREES MOTION. ALL OF THE GLOBAL
AND REGIONAL MODELS HAVE HAD A DISTINCT RIGHT-OF-TRACK BIAS BY AS
MUCH AS 10 DEGREES...AND EACH MODEL RUN HAS BEEN A LITTLE FARTHER
WEST AND SLOWER. THE EXCEPTION IS THE 06Z GFDL RUN WHICH MADE A
MAJOR SHIFT WESTWARD BY MORE 200 NMI IN THE LATER FORECAST PERIODS
...WHILE THE 06Z NOGAPS MODEL ACCELERATED ISABEL AND HAS THE
HURRICANE ONSHORE THE SOUTHEAST COAST OF NORTH CAROLINA IN 120
HOURS. HOWEVER...THE MODEL CONSENSUS IS SLOWER AND FARTHER WEST
BEFORE A TURN TO THE NORTHWEST OCCURS IN THE LATER PERIODS. THE
MODELS OBVIOUSLY HAVE NOT BEEN HANDLING THE STRONG RIDGING TO THE
NORTH OF ISABEL VERY WELL. THIS MAY BE DUE TO THE OUTFLOW ON THE
NORTH SIDE BEING DRAWN NORTHWARD AND SINKING ALONG 30N-33N...WHICH
MAY HAVE HELPED TO STRENGTHEN THE SUBTROPICAL RIDGE. WATER VAPOR
IMAGERY INDICATES THIS PATTERN HAS PERSISTED FOR MORE THAN 72 HOURS
AND CONTINUES TO SHIFT WESTWARD WITH ISABEL. THEREFORE...A GENERAL
WESTWARD MOTION SHOULD CONTINUE FOR ANOTHER 36 HOURS OR SO.
AFTERWARDS...THERE REMAINS CONSIDERABLE DIVERGENCE AMONG THE MODELS
AND HOW THEY HANDLE THE CURRENT SHORTWAVE TROUGH/LOW OVER THE
SOUTHEASTERN U.S. WATER VAPOR IMAGERY INDICATES THE TROUGH HAS
BECOME NEGATIVELY TILTED IN AN EAST-WEST ORIENTATION. THIS WOULD
SUGGEST THAT THE LOW SHOULD BEGIN TO LIFT OUT AND ALLOW THE RIDGE
NORTH OF ISABEL TO GRADUALLY BUILD WESTWARD...WHICH IS SIMILAR TO
THE 06Z GFS...GFDL...AND ETA...AND 00Z UKMET SOLUTIONS. THE KEY
WILL BE HOW THE CENTRAL U.S. TROUGH EVOLVES AND HOW DEEP IT DIGS
INTO THE SOUTHERN U.S. AND GULF OF MEXICO. THE OFFICIAL FORECAST
WAS ADJUSTED SLIGHTLY TO THE LEFT OF AND SLOWER THAN THE PREVIOUS
FORECAST...WHICH IS CONSISTENT WITH THE GUNA MODEL CONSENSUS.
HOWEVER...IT IS STILL TOO EARLY TO DETERMINE WHEN OR WHERE ISABEL
WILL MAKE LANDFALL. HOPEFULLY...THE NOAA GULFSTREAM-IV SYNOPTIC
DATA MISSION AT 14/00Z WILL PROVIDE BETTER MODEL CONVERGENCE.

ALTHOUGH ISABEL HAS A RATHER LARGE EYE DIAMETER...CONDITIONS APPEAR
FAVORABLE FOR AT LEAST SOME SLIGHT ADDITIONAL STRENGTHENING OVER
THE NEXT COUPLE OF DAYS AS THE HURRICANE MOVES OVER WARMER WATER.

FORECASTER STEWART

FORECAST POSITIONS AND MAX WINDS

INITIAL 13/1500Z 22.2N 61.5W 130 KT
12HR VT 14/0000Z 22.6N 63.0W 135 KT
24HR VT 14/1200Z 23.0N 64.8W 135 KT
36HR VT 15/0000Z 23.7N 66.7W 130 KT
48HR VT 15/1200Z 24.5N 68.7W 130 KT
72HR VT 16/1200Z 26.0N 71.0W 125 KT
96HR VT 17/1200Z 28.5N 73.0W 120 KT
120HR VT 18/1200Z 31.5N 75.0W 110 KT

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HURRICANE ISABEL DISCUSSION NUMBER 31
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
5 PM EDT SAT SEP 13 2003

THERE HAS BEEN A PLETHORA OF WIND DATA FROM BOTH THE AIR FORCE
RESERVE AND NOAA HURRICANE HUNTERS THIS AFTERNOON. IN SUMMARY...THE
AIRCRAFT FOUND MAXIMUM 700 MB FLIGHT-LEVEL WINDS OF 157 AND 158 KT
...ALONG WITH A DROPSONDE WIND VALUE OF 178 KT...OR 205 MPH...AT
879 MB...ALL OF WHICH CORRESPONDS TO SURFACE WIND ESTIMATES OF
141-142 KT. THEREFORE...THE INITIAL INTENSITY HAS BEEN INCREASED TO
140 KT/160 MPH...SO ISABEL IS A CATEGORY 5 HURRICANE ONCE AGAIN.

THE INITIAL MOTION ESTIMATE IS NOW 285/11. THIS MAY BE A SHORT-TERM
ACCELERATION DUE TO THE EYE CONTRACTING DOWN IN SIZE AND
RE-ADJUSTING WITHIN THE CENTRAL DEEP CONVECTION. HOWEVER...THE 285
DEGREES MOTION NOW APPEARS TO BE A STEADY TREND. THE NEW 12Z GFS
FORECAST TRACK HAS COME IN ALMOST ON TOP OF THE PREVIOUS OFFICAL
FORECAST THROUGH 48 HOURS AND THEN IS LEFT OF THE TRACK BY 72 HOURS
...BEFORE HOOKING BACK ACROSS THE PREVIOUS FORECAST TRACK AND
ACCELERATING ISABEL NORTHWARD. THIS SCENARIO IS ALSO IDENTICAL TO
THE 12Z ETA MODEL RUN. SIMILARLY BUT TO THE RIGHT OF THE PREVIOUS
FORECAST ARE THE GFDL...NOGAPS...UKMET...AND CANADIAN MODELS.
INTERESTINGLY ENOUGH...ALL OF THE MODELS AGREE ON A SHARP DECREASE
IN FORWARD SPEED OR A STALL IN 60-72 HOURS...AND THEN RAPIDLY
ACCELERATING ISABEL NORTH OR NORTH-NORTHWESTWARD AFTER 96 HOURS AS
THE CYCLONE IS FORECAST TO GET PICKED UP BY AN APPROACHING
SHORTWAVE TROUGH FROM THE WEST AND A BUILDING RIDGE TO THE EAST.
HOWEVER...THERE IS STILL SOME UNCERTAINTY ON THE CURRENT STRENGTH
OF THE SUBTROPICAL RIDGE TO THE NORTH OF ISABEL...SO IT IS PRUDENT
TO WAIT UNTIL ALL OF THE NOAA GULFSTREAM-IV DROPSONDE DATA MAKE IT
INTO THE 14/00Z MODELS. THE OFFICIAL FORECAST TRACK IS JUST AN
UPDATE OF THE PREVIOUS TRACK THROUGH 96 HOURS...WITH A LITTLE MORE
NORTHWARD ACCELERATION INDICATED AT 120 HOURS AS A COURSE OF LEAST
REGRET. NOTE -- NONE OF THE NHC MODEL GUIDANCE HAS ISABEL OVER LAND
BY 120 HOURS.

WHILE SOME SLIGHT STRENGTHENING IS POSSIBLE IN THE NEXT 12 HOURS...
THERE IS NO WAY TO REALLY TIME THE DEVELOPMENT OF ANOTHER EYEWALL
REPLACEMENT CYCLE. IN THE LONG RUN...UPPER-LEVEL CONDITIONS ARE
FORECAST TO REMAIN FAVORABLE FOR AT LEAST THE NEXT 48-72 HOURS...
WITH THE HURRICANE ALSO MOVING OVER WARMER WATER. THEREFORE...A
STEADY INTENSITY OR ONLY VERY SLOW WEAKENING IS EXPECTED FOR THE
NEXT COUPLE OF DAYS. BY 120 HOURS...ISABEL MAY BEGIN TO
EXPERIENCING UPPER-LEVEL SOUTH TO SOUTHWESTERLY SHEAR...WHICH
SHOULD BRING ABOUT MORE RAPID WEAKENING. HOWEVER...ISABEL IS STILL
EXPECTED TO REMAIN A MAJOR HURRICANE THOUGHOUT THE FORECAST PERIOD.

FORECASTER STEWART

FORECAST POSITIONS AND MAX WINDS

INITIAL 13/2100Z 22.6N 62.6W 140 KT
12HR VT 14/0600Z 23.0N 64.2W 140 KT
24HR VT 14/1800Z 23.7N 66.2W 140 KT
36HR VT 15/0600Z 24.4N 68.0W 135 KT
48HR VT 15/1800Z 25.2N 69.4W 135 KT
72HR VT 16/1800Z 26.5N 71.5W 130 KT
96HR VT 17/1800Z 29.5N 73.0W 125 KT
120HR VT 18/1800Z 33.5N 75.0W 105 KT

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CZC MIATCDAT3 ALL
TTAA00 KNHC DDHHMM
HURRICANE ISABEL DISCUSSION NUMBER 32
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
11 PM EDT SAT SEP 13 2003

SATELLITE IMAGES SHOW THAT CLOUD TOPS HAVE WARMED OVER THE PAST 6
HOURS AND ISABEL MAY HAVE WEAKENED A LITTLE. BUT SINCE THE PREVIOUS
ADVISORY VALUE OF 140 KNOTS WAS BASED ON AIRCRAFT RECONNAISSANCE
AND THE NEXT RECONNAISSANCE MISSION IS AT 06Z...THE OFFICIAL WIND
SPEED IS KEPT THE SAME AS THE PREVIOUS ADVISORY VALUE OF 140 KNOTS.

THE GLOBAL MODELS GENERALLY SHOW LITTLE CHANGE IN WIND SPEED FOR 5
DAYS BUT THE SHIPS STATISTICAL DYNAMICAL MODEL GRADUALLY WEAKENS
ISABEL TO 70 KNOTS IN 5 DAYS...AS A RESULT OF INCREASING VERTICAL
SHEAR AND CLIMATOLOGY AMONG OTHER FACTORS. THE OFFICIAL FORECAST IS
FOR WEAKENING TO 100 KNOTS IN 5 DAYS...A COMPROMISE BETWEEN SHIPS
AND THE GLOBAL MODELS.

THE INITIAL MOTION IS 290/11 BASED ON THE PAST 12 HOURS OF MOTION.
THE GLOBAL MODELS ARE IN GOOD AGREEMENT ABOUT A GRADUAL TURN TOWARD
THE NORTHWEST TO NORTH-NORTHWEST OVER THE NEXT 5 DAYS. THE
HURRICANE IS FORECAST TO MOVE AROUND THE PERIPHERY OF A DEEP-LAYER
ANTICYCLONE CENTERED SOUTH OF NOVA SCOTIA. AN APPROACHING
SHORT-WAVE TROUGH MOVING ACROSS THE EASTERN UNITED STATES IS
FORECAST TO BYPASS ISABEL ON ABOUT DAY 3...BUT THE NEXT SHORT-WAVE
TROUGH SHOULD PICK UP THE HURRICANE BY ABOUT DAY 5. THE OFFICIAL
FORECAST TRACK IS ADJUSTED SLIGHTLY TO THE EAST OF THE PREVIOUS
ADVISORY BUT IS STILL CLOSE TO THE WESTERN-MOST GUIDANCE WHICH IS
THE GFS MODEL. THE OFFICIAL TRACK FORECAST SHOWS A DECREASE IN
FORWARD SPEED FOR 3 DAYS FOLLOWED BY AN INCREASE IN FORWARD SPEED
ON DAY 4 AND 5. NOTE THAT THE 5 DAY FORECAST POSITION IS RATHER
CLOSE TO THE MID-ATLANTIC U.S. COAST.

FORECASTER LAWRENCE

FORECAST POSITIONS AND MAX WINDS

INITIAL 14/0300Z 23.0N 63.7W 140 KT
12HR VT 14/1200Z 23.7N 65.4W 140 KT
24HR VT 15/0000Z 24.5N 67.3W 135 KT
36HR VT 15/1200Z 25.2N 68.7W 130 KT
48HR VT 16/0000Z 25.9N 69.8W 125 KT
72HR VT 17/0000Z 28.0N 71.6W 120 KT
96HR VT 18/0000Z 31.6N 73.4W 110 KT
120HR VT 19/0000Z 36.5N 75.0W 100 KT

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Sciencerocks
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Re: Hurricane Isabel

#10 Postby Sciencerocks » Sat May 20, 2023 7:08 pm

HURRICANE ISABEL DISCUSSION NUMBER 33
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
5 AM EDT SUN SEP 14 2003

AN AIR FORCE RECONNAISSANCE AIRCRAFT JUST MEASURED 700 MB PEAK WINDS
OF 148 AND 143 KNOTS TO THE NORTHEAST AND TO THE NORTHWEST OF THE
CENTER...RESPECTIVELY. THIS CORRESPONDS TO 135 KNOTS AT THE SURFACE
BUT ASSUMING THAT THE ENTIRE WIND FIELD HAS NOT BEEN SAMPLED...THE
INITIAL INTENSITY IS KEPT AT 140 KNOTS IN THIS ADVISORY. THE
CENTRAL PRESSURE IS 938 MB. SATELLITE PRESENTATION CONTINUES TO BE
SPECTACULAR WITH A DISTINCT EYE AND OUTFLOW IN ALL QUADRANTS.
GLOBAL MODELS MAINTAIN ISABEL WITH AN AVERAGE INTENSITY OF 140
KNOTS. THIS DOES NOT APPEAR TO BE REALISTIC SINCE THE SHEAR IS
FORECAST TO INCREASE BEYOND 48 HOURS. THE OFFICIAL FORECAST CALLS
FOR SOME FLUCTUATIONS IN INTENSITY DURING THE NEXT DAY OR TWO WITH
A GRADUAL WEAKENING THEREAFTER.

THE HURRICANE HAS BEEN WOBBLING BETWEEN WEST AND WEST-NORTHWEST
DURING THE PAST FEW HOURS. HOWEVER...THE BEST ESTIMATE OF THE
INITIAL MOTION IS 290 DEGREES AT 11 KNOTS. THIS GENERAL TRACK
SHOULD CONTINUE FOR THE NEXT 12 TO 24 HOURS. A GRADUAL TURN TO THE
NORTHWEST WITH A DECREASE IN FORWARD SPEED IS ANTICIPATED AS A
SHORTWAVE SWINGS OFF THE U.S EAST COAST AND WEAKENS THE STEERING
CURRENTS. ONCE THE SHORTWAVE IS GONE IN ABOUT 72 HOURS...THE
SUBTROPICAL RIDGE IS FORECAST TO REBUILD AND ISABEL SHOULD BEGIN TO
INCREASE IN FORWARD SPEED. ON THIS TRACK...DANGEROUS ISABEL WILL BE
NEARING THE OUTER BANKS OF NORTH CAROLINA IN ABOUT 4 DAYS.

THE OFFICIAL FORECAST IS CONSISTENT WITH THE GLOBAL MODELS WHICH
UNANIMOUSLY BRING THE CORE OF THE HURRICANE TO THE U.S MID-ATLANTIC
COAST SOMEWHERE BETWEEN NORTH CAROLINA AND NEW JERSEY BETWEEN 4 OR
5 DAYS. THE OFFICIAL FORECAST IS ALSO VERY CLOSE TO THE GUNS
CONSENSUS WHICH HAS HAD A VERY LOW ERROR SO FAR.

FORECASTER AVILA

FORECAST POSITIONS AND MAX WINDS

INITIAL 14/0900Z 23.3N 65.2W 140 KT
12HR VT 14/1800Z 23.8N 66.8W 140 KT
24HR VT 15/0600Z 24.5N 68.5W 135 KT
36HR VT 15/1800Z 25.5N 69.5W 130 KT
48HR VT 16/0600Z 26.5N 70.5W 125 KT
72HR VT 17/0600Z 29.0N 72.5W 120 KT
96HR VT 18/0600Z 33.1N 75.0W 110 KT
120HR VT 19/0600Z 39.5N 77.0W 100 KT...INLAND

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HURRICANE ISABEL DISCUSSION NUMBER 34
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
11 AM EDT SUN SEP 14 2003

SATELLITE IMAGERY SUGGESTS THAT ISABEL HAS WEAKENED DURING THE PAST
6 HOURS OR SO. EYEWALL CLOUD TOPS HAVE WARMED TO ABOVE -70C AND THE
THREE SATELLITE AGENCIES HAVE COME IN WITH A CONSENSUS INTENSITY
ESTIMATE OF T6.5...OR 127 KT. THE EYE REMAINS VERY DISTINCT AND
CIRCULAR...ALBEIT WITH AN UNUSUALLY LARGE 40 NMI DIAMETER. THE
INTENSITY HAS ONLY BEEN DECREASED SLIGHTLY DOWN TO 135 KT SINCE THE
EYE HAS BECOME EMBEDDED DIRECTLY IN THE CENTER OF THE CENTRAL DEEP
CONVECTION. SUCH PERFECT SYMMETRY OFTENTIMES INDICATES A CYCLONE
STRONGER THAN SATELLITE THE ESTIMATES...WHICH WAS THE CASE
YESTERDAY. RECON WILL IS SCHEDULED TO INVESTIGATE THE HURRICANE
THIS AFTERNOON.

THE INITIAL MOTION ESTIMATE IS 290/10. THERE IS NO SIGNIFICANT
CHANGE TO PREVIOUS FORECAST TRACK OR REASONING. SATELLITE FIX
POSITIONS HAVE BEEN COMING IN ON TOP OF THE PREVIOUS FORECAST TRACK
AND THE LATEST 06Z NHC MODEL GUIDANCE IS ALSO NOW STRONGLY
CONVERGENT ABOUT THE PREVIOUS FORECAST TRACK. THERE WAS A SLIGHT
WESTWARD SHIFT TO THE MODEL CONSENSUS...BUT THERE IS NOW MUCH LESS
DIVERGENCE AMONG THE GLOBAL AND REGIONAL MODELS THROUGHOUT THE
FORECAST PERIOD. UNFORTUNATELY...THE MODELS ARE NOW IN EXCELLENT
AGREEMENT WITH ISABEL MAKING LANDFALL ALONG THE CENTRAL U.S. EAST
COAST IN ABOUT 4 DAYS. THERE IS STILL UNCERTAINTY ON WHERE THE
EXACT LANDFALL COULD OCCUR SINCE THE DEVELOPING CENTRAL U.S. TROUGH
COULD DEEPEN AND DIG SOUTHWARD MORE THAN IS FORECAST BY THE GLOBAL
MODELS...WHICH COULD LEAD A MORE NORTHWARD MOTION AND LANDFALL
FARTHER UP THE EAST COAST THAN WHAT IS CURRENTLY FORECAST.
UNFORTUNATELY...ALL OF THE MODEL GUIDANCE AGREE ON A LARGE AND
STRONG NORTH-SOUTH ORIENTED RIDGE REMAINING EAST OF ISABEL...WHICH
SHOULD PREVENT THE POWERFUL HURRICANE FROM RECURVING OUT TO SEA.
LANDFALL ALONG THE U.S MID-ATLANTIC COAST SOMEWHERE BETWEEN NORTH
CAROLINA AND NEW JERSEY BETWEEN 4 OR 5 DAYS IS APPEARING MORE AND
MORE LIKELY.

ONLY MINOR FLUCTUATIONS IN INTENSITY ARE EXPECTED FOR THE NEXT 3
DAYS AS ISABEL IS FORECAST TO MOVE OVER SIGHTLY WARMER WATER AND
REMAIN IN A FAVORABLE DOUBLE-OUTFLOW PATTERN. HOWEVER...BY 96
HOURS...ISABEL IS EXPECTED TO BE ACCELERATING NORTH-NORTHWESTWARD
UNDER INCREASING SOUTHERLY UPPER-LEVEL FLOW. HOWEVER...ALL OF THE
MODELS ARE IN GOOD AGREEMENT ON THE CENTRAL CORE OF ISABEL
REMAINING EAST OF THE STRONG JETSTREAM AND UNDER 20-25 KT 200 MB
WIND. THIS WOULD TEND TO KEEP ISABEL STRONGER THAN WHAT THE SHIPS
INTENSITY MODEL IS INDICATING...ESPECIALLY SINCE ISABEL WILL BE
MOVING OVER THE WARM GULFSTREAM SOUTH OF THE NORTH CAROLINA OUTER
BANKS AT THAT TIME. THEREFORE...LITTLE OR NO SIGNIFICANT WEAKENING
IS EXPECTED TO OCCUR UNTIL AFTER LANDFALL OCCURS.

FORECASTER STEWART

FORECAST POSITIONS AND MAX WINDS

INITIAL 14/1500Z 23.7N 66.3W 135 KT
12HR VT 15/0000Z 24.2N 67.9W 135 KT
24HR VT 15/1200Z 25.2N 69.6W 135 KT
36HR VT 16/0000Z 26.1N 70.6W 130 KT
48HR VT 16/1200Z 27.2N 71.6W 125 KT
72HR VT 17/1200Z 30.0N 73.2W 120 KT
96HR VT 18/1200Z 34.5N 75.5W 110 KT...NEAR NORTH CAROLINA
120HR VT 19/1200Z 41.0N 77.5W 70 KT...INLAND

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HURRICANE ISABEL DISCUSSION NUMBER 35
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
5 PM EDT SUN SEP 14 2003

THE AFTERNOON PLETHORA OF RECON WIND AND PRESSURE DATA INDICATE THAT
ISABEL REMAINS BARELY BELOW CATEGORY 5 INTENSITY. AIR FORCE RESERVE
HURRICANE HUNTERS MEASURED 700 MB FLIGHT-LEVEL WINDS OF 150 KT...OR
135 KT SURFACE EQUIVALENT...IN THE NORTHEAST QUADRANT OF THE
EYEWALL...WHILE A NOAA HURRICANE HUNTER DROPSONDE REPORT INDICATED
171 KT AVERAGE WINDS IN THE LOWER 150 METERS...OR 139 SURFACE WIND
EQUIVALENT. BASED ON THIS INFORMATION...ISABEL IS BEING MAINTAINED
AT 135 KT. THE OUTFLOW PATTERN REMAINS VERY IMPRESSIVE AND HAS
CONTINUED TO EXPAND.

THE INITIAL MOTION ESTIMATE IS 290/11. THERE IS NO SIGNIFICANT
CHANGE TO THE PREVIOUS 2 FORECAST TRACKS OR REASONINGS. RECON FIX
POSITIONS HAVE BEEN COMING IN RIGHT ON TRACK AND THE LATEST 12Z NHC
MODEL GUIDANCE CONTINUES TO CONVERGE ABOUT THE PREVIOUS 2 FORECAST
TRACKS. THE LATEST GFDL RUN HAS CONTINUED ITS WESTWARD SHIFT IN THE
FORECAST TRACK AND THE 96-120H TRACK IS AT LEAST 90 NMI WEST OF THE
00Z TRACK. ONE DISTURBING BIT OF INFORMATION IS THAT THE 12Z
UKMET... GFS...GFDL...AND CANADIAN MODELS DID NOT ANALYZE THE 500
MB HEIGHT AND WIND FIELDS TO THE 12Z BERMUDA UPPER-AIR OBSERVATION
OF 10 KT NORTHEAST WIND AND 5940 METER HEIGHT. THIS OBSERVATION
SUGGESTS THAT THE RIDGE TO THE NORTH OF BERMUDA AND ISABEL EXTENDS
SOUTHWESTWARD FARTHER THAN THOSE FOUR MODELS ARE INDICATING. MORE
RIDGING WOULD SUGGEST THAT...AT LEAST IN THE SHORT TERM... ISABEL
SHOULD MOVE FARTHER WEST THAN THESE MODELS ARE FORECASTING BEFORE
THE HURRICANE BEGINS TO TURN NORTHWESTWARD. ONLY THE NOGAPS MODEL
INITIALIZED THE 500 MB PROPERLY TO THE BERMUDA OBSERVATION...AND
THE 12Z NOGAPS TRACK IS TO THE LEFT OR WEST OF THE PREVIOUS AND
CURRENT FORECAST TRACKS. THE OFFICIAL FORECAST TRACK IS JUST AN
EXTENSION OF THE PREVIOUS TRACK AND IS A LITTLE TO THE WEST AND
SLIGHTLY FASTER THAN THE MODEL CONSENSUS. THERE REMAINS SOME
UNCERTAINTY ON WHERE THE EXACT LANDFALL OF ISABEL COULD OCCUR SINCE
THE DEVELOPING CENTRAL U.S. TROUGH COULD STILL DEEPEN AND DIG MORE
SOUTHWARD THAN THE MODELS ARE INDICATING. THIS COULD INDUCE A MORE
NORTHWARD MOTION AND RESULT IN LANDFALL FARTHER UP THE U.S. EAST
COAST. BUT AS IN THE PREVIOUS SEVERAL MODEL RUNS...A LARGE AND VERY
STRONG NORTH-SOUTH ORIENTED RIDGE IS FORECAST TO REMAIN EAST OF
ISABEL AND PREVENT THE HURRICANE FROM RECURVING NORTHEASTWARD.

ONLY MINOR FLUCTUATIONS IN INTENSITY ARE EXPECTED FOR THE NEXT
COUPLE OF DAYS AS ISABEL IS FORECAST TO MOVE OVER SIGHTLY WARMER
WATER AND REMAIN IN A FAVORABLE UPPER-LEVEL OUTFLOW PATTERN. BY 96
HOURS...ISABEL IS FORECAST TO BEGIN ACCELERATING NORTH OR
NORTH-NORTHWESTWARD UNDER INCREASING SOUTHERLY UPPER-LEVEL FLOW.
HOWEVER...THE CENTRAL CORE OF ISABEL IS EXPECTED TO REMAIN EAST OF
THE STRONGEST WINDS AND UNDER 15-25 KT 200 MB FLOW. THIS WOULD TEND
TO KEEP ISABEL STRONGER THAN WHAT THE SHIPS INTENSITY MODEL HAS
BEEN INDICATING...ESPECIALLY SINCE ISABEL WILL BE MOVING OVER THE
WARM GULFSTREAM OFFSHORE NORTH CAROLINA JUST PRIOR TO LANDFALL.

FORECASTER STEWART

FORECAST POSITIONS AND MAX WINDS

INITIAL 14/2100Z 24.1N 67.4W 135 KT
12HR VT 15/0600Z 24.7N 68.9W 135 KT
24HR VT 15/1800Z 25.7N 70.2W 135 KT
36HR VT 16/0600Z 26.7N 71.3W 130 KT
48HR VT 16/1800Z 28.0N 72.2W 125 KT
72HR VT 17/1800Z 31.2N 74.0W 120 KT
96HR VT 18/1800Z 36.5N 76.0W 105 KT
120HR VT 19/1800Z 43.5N 78.0W 35 KT...INLAND

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HURRICANE ISABEL DISCUSSION NUMBER 36
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
11 PM EDT SUN SEP 14 2003

RECONNAISSANCE AIRCRAFT DATA CONFIRMED 135-KNOT SURFACE WINDS AT 18Z
AND THERE WILL BE ANOTHER MISSION AT 06Z...SO THE INITIAL OFFICIAL
INTENSITY IS LEFT AT 135 KNOTS. SATELLITE IMAGES SHOW THAT CLOUD
TOPS HAVE WARMED TODAY BUT A LARGE WELL-DEFINED IMPRESSIVE EYE
PERSISTS AS WELL AS IMPRESSIVE CLOUD SYMMETRY.

THE INITIAL MOTION IS 290/11...IT HAS REMAINED THE SAME FOR OVER 24
HOURS. THE TRACK GUIDANCE ALSO REMAINS ABOUT THE SAME WITH THE
GLOBAL MODELS CLOSELY CLUSTERED AND SHOWING A LANDFALL IN JUST
UNDER 96 HOURS ALONG THE MID ATLANTIC COAST. THE SCENARIO CONSISTS
OF A DEEP-LAYER MEAN HIGH SOUTH OF NOVA SCOTIA AND TWO SHORT WAVES
MOVING ACROSS THE EASTERN UNITED STATES IN THE NEXT 5 DAYS. THE
FIRST TROUGH WILL SLOW ISABELS FORWARD SPEED WHILE IT TURNS
NORTH-NORTHWESTWARD AROUND THE PERIPHERY OF THE HIGH. THE SECOND
TROUGH WILL CAUSE AN ACCELERATION TOWARD THE NORTH-NORTHWEST WITH
ISABEL MOVING OVER THE GREAT LAKES AND BECOMING EXTRATROPICAL BY
DAY 5.

ONLY SLOW WEAKENING IS FORECAST FOR THE NEXT 4 DAYS...SO ISABEL IS
LIKELY TO STILL BE QUITE DANGEROUS AT LANDFALL. SINCE THE TRACK IS
FORECAST TO APPROACH THE COAST AT A SMALL ANGLE...A SMALL CHANGE IN
DIRECTION COULD RESULT IN A LANDFALL WELL TO THE NORTH OF THE MID
ATLANTIC COAST. ALSO OFFICIAL 4-DAY TRACK FORECAST ERRORS AVERAGE
ABOUT 275 MILES. WE INTEND THAT THE ISABEL FORECASTS WILL BE MORE
ACCURATE...BUT INTERESTS FROM THE CAROLINAS THROUGH THE NORTHEASTERN
STATES SHOULD CLOSELY MONITOR THE PROGRESS OF ISABEL.

FORECASTER LAWRENCE

FORECAST POSITIONS AND MAX WINDS

INITIAL 15/0300Z 24.5N 68.3W 135 KT
12HR VT 15/1200Z 25.2N 69.5W 135 KT
24HR VT 16/0000Z 26.2N 70.6W 130 KT
36HR VT 16/1200Z 27.6N 71.4W 125 KT
48HR VT 17/0000Z 28.9N 72.1W 120 KT
72HR VT 18/0000Z 32.8N 74.2W 115 KT
96HR VT 19/0000Z 38.3N 76.8W 90 KT...INLAND
120HR VT 20/0000Z 45.5N 80.0W 35 KT...INLAND...EXTRATROPICAL

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HURRICANE ISABEL DISCUSSION NUMBER 37
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
5 AM EDT MON SEP 15 2003

ISABEL IS SHOWING STRUCTURAL MIXED SIGNALS THIS EVENING. ON ONE
SIDE...SATELLITE IMAGERY INDICATES THE EYE REMAINS WELL DEFINED AND
THAT CLOUD TOPS NEAR THE EYE HAVE COOLED DURING THE PAST SEVERAL
HOURS. ON THE OTHER...REPORTS FROM AN AIR FORCE RESERVE HURRICANE
HUNTER INDICATE THE CENTRAL PRESSURE HAS RISEN TO 940 MB AND THAT
THE MAXIMUM FLIGHT-LEVEL WINDS ARE 138 KT. THE AIRCRAFT HAS ALSO
REPORTED WELL-DEFINED CONCENTRIC WIND MAXIMA. SUBJECTIVE SATELLITE
INTENSITY ESTIMATES ARE 115 KT...AS ARE THE LATEST OBJECTIVE
ESTIMATES. THE MAXIMUM WINDS ARE REDUCED TO 130 KT FOR THIS
ADVISORY...AND THE STORM COULD BE A LITTLE WEAKER THAN THIS.

WHILE THERE HAS BEEN A WOBBLE TO THE LEFT OVER THE PAST FEW HOURS...
THE INITIAL MOTION IS 290/9...THE SAME DIRECTION AS EARLIER. WATER
VAPOR IMAGERY SHOWS A LARGE ELONGATED RIDGE OF HIGH PRESSURE
EXTENDING FROM SOUTHEASTERN CANADA SOUTHEASTWARD TO EAST OF
ISABEL...AND WESTERLY FLOW WITH SEVERAL EMBEDDED SHORTWAVE TROUGHS
OVER THE CENTRAL AND EASTERN UNITED STATES. ISABEL SHOULD BEGIN TO
TURN NORTHWESTWARD AROUND THE WEST SIDE OF THE RIDGE DURING THE
NEXT 12-24 HR...THEN GRADUALLY ACCELERATE NORTH-NORTHWESTWARD
BETWEEN THE RIDGE AND THE BROAD TROUGHING TO THE WEST. ALL
DYNAMICAL MODEL GUIDANCE AGREES WITH THIS SCENARIO...BRINGING
ISABEL TO THE VICINITY OF THE MID-ATLANTIC COAST IN 72-96 HR. THE
OFFICIAL FORECAST TRACK IS SIMILAR TO...BUT A LITTLE WEST OF THE
PREVIOUS TRACK. SINCE THE TRACK IS FORECAST TO APPROACH THE COAST
AT A SMALL ANGLE...A SMALL CHANGE IN DIRECTION COULD RESULT IN A
LANDFALL WELL TO THE NORTH OF THE MID-ATLANTIC COAST. INTERESTS
FROM THE CAROLINAS THROUGH THE NORTHEASTERN STATES SHOULD CLOSELY
MONITOR THE PROGRESS OF ISABEL.

ISABEL IS LIKELY TO CONTINUE IN A WARM-WATER LIGHT-SHEAR ENVIRONMENT
FOR THE NEXT 36 HR...AND THUS FLUCTUATION IN INTENSITY FROM EYEWALL
CONTRACTION CYCLES ARE LIKELY. BEYOND THAT TIME...THE HURRICANE
WILL BE MOVING INTO THE UPPER-LEVEL SOUTHWESTERLY FLOW ASSOCIATED
WITH THE TROUGH OVER THE UNITED STATES...AND THUS MAY EXPERIENCE
SOME SHEAR. THE SHIPS MODEL SUGGESTS 30-40 KT OF SHEAR...AND IF
THAT VERIFIES ISABEL COULD WEAKEN CONSIDERABLY. HOWEVER...THE
LARGE-SCALE MODELS ARE NOT IN AGREEMENT ON THIS...SO THE INTENSITY
FORECAST WILL CALL FOR ONLY A MODEST WEAKENING BEFORE LANDFALL. IT
SHOULD BE NOTED THAT THE COASTAL SHELF WATER ALONG THE MID-ATLANTIC
COAST IS RATHER COLD...AND ANY TRACK EAST OF CAPE HATTERAS THAT
WOULD KEEP THE HURRICANE OVER THAT WATER WOULD LIKELY PRODUCE MORE
WEAKENING THAN CURRENTLY FORECAST.

FORECASTER BEVEN

FORECAST POSITIONS AND MAX WINDS

INITIAL 15/0900Z 24.8N 69.0W 130 KT
12HR VT 15/1800Z 25.5N 70.1W 130 KT
24HR VT 16/0600Z 26.5N 71.0W 130 KT
36HR VT 16/1800Z 27.9N 71.9W 125 KT
48HR VT 17/0600Z 29.2N 72.6W 120 KT
72HR VT 18/0600Z 33.5N 75.0W 115 KT
96HR VT 19/0600Z 40.0N 78.0W 60 KT...INLAND
120HR VT 20/0600Z 48.5N 80.0W 35 KT...INLAND EXTRATROPICAL

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HURRICANE ISABEL DISCUSSION NUMBER 38
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
11 AM EDT MON SEP 15 2003

SATELLITE IMAGERY INDICATES THAT THE INNER CORE STRUCTURE CONTINUES
TO BREAK DOWN...WITH A LESS WELL-DEFINED EYE IN VISIBLE IMAGERY.
EYEWALL CONVECTION HAS BECOME ASYMMETRIC AND FRAGMENTED...AND THE
OVERALL CONVECTIVE STRUCTURE IS NOW MORE BANDED THAN IT WAS OVER
THE PAST COUPLE OF DAYS. THE LATEST DVORAK SATELLITE INTENSITY
ESTIMATES ARE 115 KT. THE ADVISORY INTENSITY IS LOWERED TO 120 KT
AND ANOTHER RECONNAISSANCE AIRCRAFT WILL BE IN THE HURRICANE AT
18Z.

THE INITIAL MOTION IS 300/7...SLOWER THAN BEFORE. WITH THE
MID-LEVEL SHORT WAVE OFF THE CAROLINAS MOVING OUT TO THE
NORTHEAST...THE STEERING CURRENTS SURROUNDING ISABEL ARE BEGINNING
TO WEAKEN AS SOME RIDGING TEMPORARILY BUILDS IN NORTHWEST...AHEAD
OF...THE HURRICANE. THIS SHOULD RESULT IN A SLOW MOTION TO THE
NORTHWEST OVER THE NEXT DAY OR TWO. BY 48 HOURS OR SO...AN
APPROACHING TROUGH FROM THE WEST WILL HELP ACCELERATE ISABEL
NORTH-NORTHWESTWARD AROUND THE WEST SIDE OF THE DEEP-LAYER RIDGE
ANCHORED NEAR 35N AND 60 W. MODEL GUIDANCE IS IN EXCELLENT
AGREEMENT ON THIS TRACK ALTHOUGH THE GFS IS CONSIDERABLY SLOWER
THAN THE OTHER MODELS. VERY LITTLE CHANGE HAS BEEN MADE TO THE
OFFICIAL FORECAST TRACK...WHICH IS VERY CLOSE TO THE GFDL...
UKMET...NOGAPS...GFS MODEL CONSENSUS.

ALTHOUGH THERE HAS BEEN SOME RESTRICTION OF THE OUTFLOW IN THE
SOUTHWEST QUADRANT...THE CURRENT WEAKENING MAY BE MORE A RESULT OF
LESS FAVORABLE ENVIRONMENTAL THERMODYNAMICS. THERE ARE WESTERLIES
TO THE NORTH OF ISABEL...BUT THE SHEAR IS EXPECTED TO BE LIGHT FOR
THE NEXT 36 HOURS OR SO. THERE WILL BE PLENTY OF WARM WATER
UNDER THE HURRICANE UNTIL COOLER SHELF WATERS ARE ENCOUNTERED RIGHT
ALONG THE COASTLINE. ONE KEY TO THE ULTIMATE LANDFALL INTENSITY
WILL BE THE EVOLUTION OF AN UPPER-LEVEL TROUGH THAT COULD ENHANCE
THE OUTFLOW AND REDUCE THE SHEAR PRIOR TO LANDFALL IF IT DIGS AS
SHARPLY AS FORECAST BY THE GFS. WITH THIS IN MIND...ISABEL COULD
STILL BE A MAJOR HURRICANE AT LANDFALL.

FORECASTER FRANKLIN

FORECAST POSITIONS AND MAX WINDS

INITIAL 15/1500Z 25.2N 69.4W 120 KT
12HR VT 16/0000Z 25.8N 70.3W 115 KT
24HR VT 16/1200Z 27.0N 71.2W 115 KT
36HR VT 17/0000Z 28.2N 72.0W 115 KT
48HR VT 17/1200Z 30.0N 73.0W 115 KT
72HR VT 18/1200Z 34.5N 75.5W 110 KT
96HR VT 19/1200Z 40.0N 78.0W 60 KT...INLAND
120HR VT 20/1200Z 49.5N 80.0W 30 KT...EXTRATROPICAL

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HURRICANE ISABEL DISCUSSION NUMBER 39
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
5 PM EDT MON SEP 15 2003

AIRCRAFT RECONNAISSANCE OBSERVATIONS CONFIRM THAT ISABEL HAS
WEAKENED TO CATEGORY THREE STATUS. PEAK FLIGHT LEVEL WINDS OF 120
KT SUPPORT SURFACE WINDS OF ABOUT 110 KT...WHICH IS THE ADVISORY
INTENSITY...ALTHOUGH DROPSONDES IN THE EYEWALL SUGGEST THE WINDS
MIGHT BE EVEN A LITTLE BIT LESS. THERE IS NOT MUCH EVIDENCE OF
SHEAR AND THE OUTFLOW PATTERN STILL LOOKS STRONG. HOWEVER...THE
EYEWALL CONVECTION REMAINS ASYMMETRIC AND THE WEST SIDE OF THE
CIRCULATION LOOKS A LITTLE DRY. ALTHOUGH ISABEL HAS BEEN
WEAKENING...AND MAY WEAKEN FURTHER...THERE IS SOME MODEL GUIDANCE
THAT SUGGESTS THAT A MORE FAVORABLE UPPER WIND PATTERN...WITH
ENHANCED ANTICYCLONIC OUTFLOW...MAY DEVELOP IN THE LAST 24 HOURS
BEFORE LANDFALL. HOWEVER...DYNAMICAL MODELS HAVE LIMITED SKILL IN
PREDICTING SUCH PATTERNS...IN PARTICULAR THEY OFTEN OVER-DEVELOP
UPPER-LEVEL ANTICYCLONES OVER TROPICAL CYCLONES. THE OFFICIAL
FORECAST SIMPLY CALLS FOR LITTLE CHANGE IN STRENGTH...AND
ANTICIPATES A MAJOR HURRICANE...CATEGORY THREE OR HIGHER...AT
LANDFALL.

THE INITIAL MOTION IS NOW 305/7...OR NORTHWEST. MODEL GUIDANCE
REMAINS VERY TIGHTLY CLUSTERED...EVEN MORE SO THAN THIS MORNING AS
THE 12Z GFS IS A LITTLE FASTER THAN ITS EARLIER RUN. THERE HAS BEEN
NO SIGNIFICANT CHANGE TO THE FORECAST TRACK. HOWEVER...SOME OF THE
GUIDANCE IS SUGGESTING THAT THE MOTION OVER THE NEXT DAY OR TWO MAY
BE A LITTLE MORE NORTHWARD BEFORE ISABEL TURNS BACK TO THE
NORTHWEST...AFTER THE UPPER TROUGH CURRENTLY OVER THE GREAT LAKES
MOVES OUT AND HIGH PRESSURE BUILDS AGAIN NORTH OF THE HURRICANE.
BY 48 HOURS OR SO...AN APPROACHING MID- TO UPPER-LEVEL TROUGH FROM
THE WEST WILL HELP ACCELERATE ISABEL NORTH-NORTHWESTWARD AROUND THE
WEST SIDE OF THE DEEP-LAYER RIDGE ANCHORED NEAR 35N AND 60 W.

FORECASTER FRANKLIN/PASCH

FORECAST POSITIONS AND MAX WINDS

INITIAL 15/2100Z 25.6N 70.0W 110 KT
12HR VT 16/0600Z 26.3N 70.8W 110 KT
24HR VT 16/1800Z 27.5N 71.6W 105 KT
36HR VT 17/0600Z 29.0N 72.3W 105 KT
48HR VT 17/1800Z 30.8N 73.2W 105 KT
72HR VT 18/1800Z 35.5N 76.0W 100 KT...INLAND
96HR VT 19/1800Z 42.0N 79.0W 50 KT...INLAND
120HR VT 20/1800Z 52.0N 80.0W 30 KT...EXTRATROPICAL
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HURRICANE ISABEL DISCUSSION NUMBER 40
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
11 PM EDT MON SEP 15 2003

THE DEEP CONVECTION HAS CONTINUED TO ERODE ON THE WEST SIDE OF
ISABEL SINCE THE 18Z RECONNAISSANCE AIRCRAFT DATA INDICATED 110
KNOTS...SO THE ADVISORY INITIAL WIND SPEED IS REDUCED 5 KNOTS TO
105 KNOTS. THE SHIPS MODEL AS WELL AS SEVERAL OF THE GLOBAL MODELS
INDICATE LITTLE CHANGE IN WIND SPEED BEFORE LANDFALL WHICH IS
EXPECTED BETWEEN 48 AND 60 HOURS. THE SHIPS MODEL DIAGNOSES THE
GFS VERTICAL SHEAR NEAR 30 KNOTS AT 48 HOURS SO IT IS DIFFICULT TO
UNDERSTAND WHY THE GUIDANCE DOES NOT CALL FOR MORE WEAKENING BEFORE
LANDFALL. PERHAPS IT IS THE PATH OVER THE GULFSTREAM THAT WILL
KEEP THE WIND SPEED UP. ANYWAY THE OFFICIAL WIND SPEED IS REDUCED
ONLY 5 MORE KNOTS BEFORE LANDFALL TO 100 KNOTS...STILL A CATEGORY
THREE HURRICANE ON THE SAFFIR SIMPSON SCALE.

THE FORECAST TRACK AND SCENARIO IS VERY SIMILAR TO THE PREVIOUS
ADVISORY. THE INITIAL MOTION ESTIMATE IS 320/06. THE GUIDANCE IS
TIGHTLY CLUSTERED ABOUT A NORTH-NORTHWESTWARD TRACK AT LESS THAN 10
KNOTS FORWARD SPEED FOR 48 HOURS AS THE HURRICANE MOVES AROUND THE
WEST SIDE OF A DEEP-LAYER MEAN RIDGE WHILE BEING BYPASSED BY A
SHORT-WAVE TROUGH. A SECOND SHORT-WAVE TROUGH WILL ACCELERATE THE
TRACK NORTH-NORTHWESTWARD WITH THE CENTER INLAND IN 72 HOURS.

FORECASTER LAWRENCE

FORECAST POSITIONS AND MAX WINDS

INITIAL 16/0300Z 26.1N 70.2W 105 KT
12HR VT 16/1200Z 26.9N 70.8W 105 KT
24HR VT 17/0000Z 28.4N 71.7W 100 KT
36HR VT 17/1200Z 29.8N 72.5W 100 KT
48HR VT 18/0000Z 31.5N 73.7W 100 KT
72HR VT 19/0000Z 37.2N 77.2W 60 KT...INLAND
96HR VT 20/0000Z 44.5N 79.5W 40 KT...INLAND...EXTRATROPICAL
120HR VT 21/0000Z 54.0N 78.5W 30 KT...INLAND...EXTRATROPICAL


NNNN
https://www.youtube.com/watch?v=ow_fH0P4wV4

HURRICANE ISABEL DISCUSSION NUMBER 41
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
5 AM EDT TUE SEP 16 2003

SATELLITE IMAGERY AND AIR FORCE RESERVE HURRICANE HUNTER DATA
INDICATE THAT ISABEL HAS BECOME QUITE DISORGANIZED DURING THE PAST
6-12 HR. CENTER FIXES FROM IR IMAGERY ARE 20-25 NM EAST OF THE
FIXES FROM THE AIR FORCE RESERVE HURRICANE HUNTER AIRCRAFT AND
MICROWAVE DATA...SUGGESTING WESTERLY SHEAR IS AFFECTING THE SYSTEM.
THE AIRCRAFT REPORTS THAT THE WIND FIELD HAS SPREAD OUT...WITH AN
INNER RADIUS OF MAXIMUM WIND OF 40 NM AND SEVERAL MAXIMA PRESENT
OUTSIDE OF THAT. THE MAXIMUM FLIGHT-LEVEL WINDS HAVE BEEN 101
KT...AND THE LATEST CENTRAL PRESSURE IS 956 MB. THE MAXIMUM
WINDS ARE REDUCED TO 100 KT...AND THIS IS LIKELY GENEROUS.

THE INITIAL MOTION IS NOW 325/6. THE TRACK FORECAST IS REASONABLY
STRAIGHT FORWARD. ISABEL IS ON THE WEST SIDE OF A DEEP-LAYER RIDGE
EXTENDING FROM THE CANADIAN MARITIMES SOUTH-SOUTHEASTWARD TO EAST
OF THE HURRICANE. A BROAD AREA OF WESTERLY FLOW IS OVER THE
CENTRAL AND EASTERN UNITED STATES...WITH A SHORTWAVE TROUGH LIFTING
NORTHEASTWARD THROUGH THE GREAT LAKES. LARGE-SCALE MODELS INDICATE
THAT THE RIDGE SHOULD BUILD SOMEWHAT WESTWARD AS THE SHORTWAVE
LIFTS OUT...WHICH SHOULD CAUSE ISABEL TO MOVE IN A GENERAL
NORTHWEST OR NORTH-NORTHWESTERLY DIRECTION THROUGH 72 HR. AFTER
THAT...THE STORM SHOULD TURN NORTHWARD AND NORTH-NORTHEASTWARD AS
IT MERGES WITH THE NEXT STRONG SHORTWAVE TROUGH MOVING EASTWARD
ACROSS THE NORTHERN UNITED STATES. ALL DYNAMICAL MODELS AGREE WITH
THIS SCENARIO...AS DOES THE OFFICIAL FORECAST WHICH IS MOSTLY AN
UPDATE OF THE PREVIOUS PACKAGE. IT SHOULD BE NOTED THAT WHILE THE
FORECAST CURRENTLY CALLS FOR LANDFALL IN NORTH CAROLINA IN ABOUT 60
HR...IT WOULD ONLY TAKE A 10 DEGREE CHANGE TO THE RIGHT FOR ISABEL
TO MAKE LANDFALL ON THE DELMARVA PENINSULA AS SHOWN IN THE CANADIAN
MODEL.

THE INTENSITY FORECAST IS VERY PROBLEMATIC. LARGE-SCALE MODELS
SUGGEST THAT THE CURRENT SHEAR COULD CONTINUE FOR ANOTHER 12-24 HR.
BEYOND THAT TIME...THE MODELS ALL FORECAST THE DEVELOPMENT OF A
NEGATIVELY-TILTED SHORTWAVE TROUGH OVER THE SOUTHEASTERN UNITED
STATES. WHILE THIS TROUGH MAY NOT REDUCE THE SHEAR...IT COULD
PROVIDE A BETTER OUTFLOW PATTERN AND DYNAMICAL FORCING TO SUSTAIN
OR STRENGTHEN THE STORM. ON THE OTHER HAND...ISABEL'S BROAD WIND
FIELD SUGGESTS THAT THE STORM MIGHT BE SLOW TO RESPOND TO A MORE
FAVORABLE ENVIRONMENT...AND THUS MIGHT MOVE ASHORE BEFORE
SIGNIFICANT STRENGTHENING COULD OCCUR. THERE ARE THREE POSSIBLE
SCENARIOS. FIRST...CONTINUED WEAKENING DUE TO SHEAR AS FORECAST BY
THE SHIPS MODEL. SECOND...CONTINUED SHORT-TERM WEAKENING FOLLWED
BY RE-INTENSIFICATION AS ISABEL APPROACHES THE COAST. THIRD...A
RELATIVELY STEADY-STATE HURRICANE UNTIL LANDFALL. THE INTENSITY
FORECAST WILL GO WITH THE THIRD SCENARIO AT THIS TIME.


FORECASTER BEVEN

FORECAST POSITIONS AND MAX WINDS

INITIAL 16/0900Z 26.6N 70.7W 100 KT
12HR VT 16/1800Z 27.6N 71.2W 100 KT
24HR VT 17/0600Z 29.0N 72.1W 100 KT
36HR VT 17/1800Z 30.7N 73.2W 100 KT
48HR VT 18/0600Z 33.0N 74.7W 100 KT
72HR VT 19/0600Z 38.0N 78.5W 55 KT...INLAND
96HR VT 20/0600Z 45.5N 79.0W 40 KT...INLAND EXTRATROPICAL
120HR VT 21/0600Z 55.0N 76.0W 30 KT...INLAND EXTRATROPICAL
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Sciencerocks
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Re: Hurricane Isabel

#11 Postby Sciencerocks » Sat May 20, 2023 7:15 pm

HURRICANE ISABEL DISCUSSION NUMBER 42
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
11 AM EDT TUE SEP 16 2003

A NOAA HURRICANE HUNTER AIRCRAFT REPORTED THAT THE CENTRAL PRESSURE
CONTINUES TO SLOWLY RISE AND THE EYE HAS BECOME POORLY DEFINED ON A
RADAR IMAGE TRANSMITTED FROM THE AIRCRAFT. PEAK FLIGHT-LEVEL WINDS
WERE 105 KT IN THE NORTHWEST QUADRANT FROM 7000 FT...WHICH WOULD
SUPPORT SURFACE WINDS OF ABOUT 90 KT. THIS MAKES ISABEL A CATEGORY
TWO HURRICANE ON THE SAFFIR-SIMPSON SCALE. WATER VAPOR IMAGERY
CONTINUES TO SHOW DRY AIR IN THE WESTERN PART OF THE CIRCULATION...
AND THE CONVECTION HAS WEAKENED MARKEDLY OVER PAST FEW HOURS.
RECENT IMAGES...HOWEVER...SHOW AN IMPROVEMENT IN THE OUTFLOW
PATTERN NORTHWEST OF THE CENTER.

THE INITIAL MOTION IS 330/7. THERE HAS BEEN NO SIGNIFICANT CHANGE TO
THE TRACK FORECAST. ISABEL IS ON THE WEST SIDE OF A DEEP-LAYER
RIDGE EXTENDING FROM THE CANADIAN MARITIMES SOUTH-SOUTHEASTWARD TO
EAST OF THE HURRICANE. A BROAD AREA OF WESTERLY FLOW IS OVER THE
CENTRAL AND EASTERN UNITED STATES...WITH A SHORTWAVE TROUGH LIFTING
NORTHEASTWARD THROUGH THE GREAT LAKES. LARGE-SCALE MODELS INDICATE
THAT THE RIDGE SHOULD BUILD WESTWARD AS THE SHORTWAVE LIFTS OUT...
WHICH SHOULD CAUSE ISABEL TO MOVE IN A GENERAL NORTH- NORTHWESTERLY
DIRECTION THROUGH 72 HR.

WITH THE DETERIORATION OF THE CENTRAL CORE...ADDITIONAL WEAKENING
SEEMS LIKELY OVER THE NEXT 24 HOURS. MOST OF THE MODEL GUIDANCE
CONTINUES TO SHOW INCREASING ANTICYCLONIC OUTFLOW OVER ISABEL AS A
RESULT OF A DIGGING AND NEGATIVELY-TILTED UPPER-LEVEL TROUGH THAT
SHOULD INTERACT WITH THE HURRICANE IN THE 24 HOURS PRIOR TO
LANDFALL. FOR THIS REASON...THE OFFICIAL FORECAST ALLOWS FOR SOME
RESTRENGTHENING. IT IS POSSIBLE...HOWEVER...THAT THE CIRCULATION
COULD BECOME SO DISRUPTED OVER THE NEXT DAY OR SO THAT ISABEL WOULD
BE UNABLE TO RESPOND TO THE MORE FAVORABLE UPPER-LEVEL FORCING.

FORECASTER FRANKLIN

FORECAST POSITIONS AND MAX WINDS

INITIAL 16/1500Z 27.4N 71.2W 90 KT
12HR VT 17/0000Z 28.4N 71.8W 85 KT
24HR VT 17/1200Z 29.9N 72.6W 85 KT
36HR VT 18/0000Z 31.7N 73.9W 90 KT
48HR VT 18/1200Z 33.8N 75.6W 95 KT
72HR VT 19/1200Z 39.0N 79.0W 45 KT...INLAND
96HR VT 20/1200Z 47.0N 78.5W 30 KT...EXTRATROPICAL
120HR VT 21/1200Z 54.0N 71.0W 30 KT...EXTRATROPICAL

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HURRICANE ISABEL DISCUSSION NUMBER 43
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
5 PM EDT TUE SEP 16 2003

RECENT FIXES FROM NOAA AND AIR FORCE RESERVE HURRICANE HUNTER
AIRCRAFT INDICATE THAT THE WEAKENING TREND HAS ENDED...AT LEAST FOR
THE TIME BEING. THE MOST RECENT PEAK FLIGHT-LEVEL WIND REPORTED BY
THE AIR FORCE AIRCRAFT WAS 111 KT OVER A VERY SMALL AREA IN THE
NORTHEAST QUADRANT...AND THE CREW INDICATED AN IMPROVED RADAR
PRESENTATION. BEFORE INCREASING THE ADVISORY INTENSITY...WE WOULD
LIKE TO MAKE SURE THESE WINDS ARE REPRESENTATIVE. WHILE THE
OUTFLOW PATTERN HAS BEEN IMPROVING TODAY...THE CORE CONVECTION IS
STILL RATHER THIN.

THE INITIAL MOTION REMAINS 330/7. THERE CONTINUES TO BE NO
SIGNIFICANT CHANGE TO THE TRACK FORECAST. ISABEL IS ON THE WEST
SIDE OF A DEEP-LAYER RIDGE EXTENDING FROM THE CANADIAN MARITIMES
SOUTH-SOUTHEASTWARD TO EAST OF THE HURRICANE. A BROAD AREA OF
WESTERLY FLOW IS OVER THE CENTRAL AND EASTERN UNITED STATES...WITH
A SHORTWAVE TROUGH LIFTING NORTHEASTWARD FROM THE GREAT LAKES.
LARGE-SCALE MODELS INDICATE THAT THE RIDGE SHOULD BUILD WESTWARD AS
THE SHORTWAVE LIFTS OUT. THIS COULD CAUSE THE TRACK TO BEND
SLIGHTLY TO THE LEFT OF THE CURRENT HEADING...AND THIS IS REFLECTED
IN THE OFFICIAL FORECAST.

MOST OF THE DYNAMICAL MODELS CONTINUE TO FORECAST THE DEVELOPMENT OF
A MORE FAVORABLE UPPER-LEVEL ANTICYCLONIC OUTFLOW PATTERN AS ISABEL
APPROACHES THE COAST. WATER-VAPOR IMAGERY SHOWS A SHORT WAVE
TROUGH EXTENDING INTO THE GULF OF MEXICO ALONG 90W. THE MODELS DIG
THIS SHORT WAVE TO THE SOUTHWEST OF ISABEL...CREATING AN OUTFLOW
CHANNEL OVER THE WESTERN PERIPHERY OF THE HURRICANE. THE EXPLICIT
INTENSITY GUIDANCE...THE SHIPS AND GFDL MODELS...NOW SHOW SOME
REINTENSIFICATION.

WIND RADII HAVE BEEN EXPANDED BASED ON DATA FROM THE STEPPED
FREQUENCY MICROWAVE RADIOMETER ONBOARD THE NOAA P-3 AIRCRAFT.

NOTE...THE HURRICANE HUNTER AIRCRAFT RECENTLY REPORTED A PRESSURE OF
958 MB.

FORECASTER FRANKLIN

FORECAST POSITIONS AND MAX WINDS

INITIAL 16/2100Z 27.8N 71.4W 90 KT
12HR VT 17/0600Z 28.6N 71.9W 90 KT
24HR VT 17/1800Z 30.5N 73.0W 90 KT
36HR VT 18/0600Z 32.7N 74.6W 90 KT
48HR VT 18/1800Z 35.0N 76.7W 95 KT...INLAND
72HR VT 19/1800Z 41.5N 79.5W 30 KT...INLAND
96HR VT 20/1800Z 50.0N 76.5W 30 KT...EXTRATROPICAL
120HR VT 21/1800Z...ABSORBED BY EXTRATROPICAL LOW

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[img]HURRICANE ISABEL DISCUSSION NUMBER 44
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
11 PM EDT TUE SEP 16 2003

RECENT RECON FLIGHT LEVEL WINDS OF 111 AND 109 KNOTS ARE THE BASIS
FOR INCREASING THE WIND SPEED TO 95 KNOTS. THE SHIPS AND GLOBAL
GUIDANCE MODELS SHOW LITTLE CHANGE OR SLIGHT WEAKENING BEFORE
LANDFALL. THERE HAS BEEN SOME DISCUSSION ABOUT THE APPROACH OF THE
NEXT SHORT WAVE TROUGH HAVING A FAVORABLE EFFECT ON INTENSIFICATION
...PERHAPS FROM BAROCLINIC EFFECTS OR FROM AN IMPROVED OUTFLOW
PATTERN. IN ANY CASE THE OFFICIAL FORECAST IS FOR LITTLE CHANGE IN
WIND SPEED BEFORE LANDFALL.

THE INITIAL MOTION IS 335/7. THE FORECAST TRACK AND REASONING IS
CHANGED VERY LITTLE FROM THE PREVIOUS ADVISORY. ISABEL IS ON THE
WEST SIDE OF A DEEP-LAYER RIDGE WHICH IS FORECAST TO BUILD WESTWARD
FOR 48 HOURS UNTIL THE NEXT SHORT WAVE TROUGH APPROACHES. THIS
COULD CAUSE THE TRACK TO BEND SLIGHTLY TO THE LEFT OF THE CURRENT
HEADING...AND THIS IS REFLECTED IN THE OFFICIAL FORECAST.

FORECASTER LAWRENCE

FORECAST POSITIONS AND MAX WINDS

INITIAL 17/0300Z 28.5N 71.7W 95 KT
12HR VT 17/1200Z 29.7N 72.3W 95 KT
24HR VT 18/0000Z 31.7N 73.7W 95 KT
36HR VT 18/1200Z 34.0N 75.5W 95 KT
48HR VT 19/0000Z 36.6N 77.5W 65 KT...INLAND
72HR VT 20/0000Z 43.0N 78.5W 40 KT...INLAND
96HR VT 21/0000Z 54.0N 73.5W 30 KT...INLAND...EXTRATROPICAL
120HR VT 22/0000Z 59.0N 56.0W 30 KT...INLAND...EXTRATROPICAL

HURRICANE ISABEL DISCUSSION NUMBER 45
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
5 AM EDT WED SEP 17 2003

REPORTS FROM AN AIR FORCE RESERVE HURRICANE HUNTER AIRCRAFT AND
SATELLITE IMAGERY INDICATE THAT ISABEL HAS CHANGED LITTLE IN
STRENGTH OR ORGANIZATION DURING THE PAST 6 HR. THE LATEST CENTRAL
PRESSURE REPORTED BY THE AIRCRAFT IS 958 MB...AND THE MAXIMUM 700
MB WINDS THUS FAR ARE 103 KT. THE AIRCRAFT IS REPORTING A 25-NM
WIDE EYE SIMILAR TO A FEATURE SEEN IN SATELLITE IMAGERY. HOWEVER...
THE AIRCRAFT FIXES ARE SOUTHWEST OF THE SATELLITE FIXES...AND THERE
IS NO WIND MAXIMUM ASSOCIATED WITH THE APPARENT EYEWALL. INDEED...
THE RADIUS OF MAXIMUM WINDS IS 50-70 NM. THE MAXIMUM WINDS REMAIN
95 KT FOR THIS ADVISORY.

THE INITIAL MOTION IS NOW 335/8. THERE IS NO CHANGE IN THE FORECAST
TRACK PHILOSOPHY FROM THE PREVIOUS ADVISORY. ISABEL SHOULD
CONTINUE TO TRACK GENERALLY NORTH-NORTHWESTWARD BETWEEN A DEEP-
LAYER RIDGE OVER THE WESTERN ATLANTIC AND A DEVELOPING MID/UPPER-
LEVEL TROUGH OVER THE SOUTHEASTERN UNITED STATES. THE DYNAMICAL
MODELS ARE VERY TIGHTLY CLUSTERED AROUND A LANDFALL IN EASTERN
NORTH CAROLINA IN ABOUT 36 HR...AND THE OFFICIAL FORECAST IS DOWN
THE MIDDLE OF THIS GUIDANCE. AFTER LANDFALL...ISABEL SHOULD TRACK
NORTH-NORTHWESTWARD OR PERHAPS NORTHWESTWARD FOR 12 HR OR SO...THEN
RECURVE NORTHWARD AND NORTHEASTWARD IN FRONT OF THE STRONG DEEP-
LAYER TROUGH MOVING EASTWARD ACROSS THE NORTHERN UNITED STATES.
THE NEAR-UNANIMOUS GUIDANCE MAKES THIS A HIGH CONFIDENCE
FORECAST...BUT THOSE AWAY FROM THE FORECAST TRACK SHOULD NOT LET
DOWN THEIR GUARD JUST IN CASE THE GUIDANCE PROVES TO BE UNANIMOUSLY
WRONG.

THE INTENSITY FORECAST REMAINS VERY PROBLEMATIC. ISABEL CURRENTLY
LACKS A TIGHT CENTRAL CORE AND STRONG CONVECTION...AND EVEN IN
FAVORABLE CONDITIONS WOULD LIKELY BE SLOW TO INTENSIFY. VERTICAL
SHEAR AND POSSIBLY DRY AIR STILL SEEM TO BE AFFECTING THE
SYSTEM...SO ANY SIGNIFICANT STRENGTHENING WOULD LIKELY HAVE TO WAIT
FOR AT LEAST 12 HR UNTIL THE NEGATIVELY-TILTED SHORTWAVE TROUGH
DEVELOPS OVER THE SOUTHEASTERN UNITED STATES AND IMPROVES THE
OUTFLOW. EVEN THEN...THERE IS A QUESTION OF WHETHER THE SHEAR WILL
DECREASE ENOUGH TO ALLOW STRENGTHENING. AN ADDITIONAL COMPLICATION
IS A SURFACE FRONT BETWEEN ISABEL AND THE NORTH CAROLINA COAST...
WITH OBSERVATIONS IN THE HURRICANE WARNING AREA OF COOL AIR WITH
DEWPOINTS BELOW 20C. INGESTING THAT AIR WOULD LIKELY INHIBIT
STRENGTHENING. THE INTENSITY FORECAST WILL REMAIN 95 KT UNTIL
LANDFALL BASED MAINLY ON THE PREMISE THAT THE LARGE AND SPRAWLING
VORTEX WILL BE SLOW TO RESPOND TO CHANGES IN THE ENVIRONMENT...
EITHER FAVORABLE OR UNFAVORABLE. HOWEVER...OTHER POSSIBLE
SCENARIOS INCLUDE STRENGTHENING DUE TO FORCING FROM THE TROUGH...
AND WEAKENING DUE TO VERTICAL SHEAR AND COLD AIR INTRUSION.

FORECASTER BEVEN

FORECAST POSITIONS AND MAX WINDS

INITIAL 17/0900Z 29.4N 72.2W 95 KT
12HR VT 17/1800Z 30.8N 73.0W 95 KT
24HR VT 18/0600Z 33.0N 74.6W 95 KT
36HR VT 18/1800Z 35.2N 76.4W 95 KT...INLAND
48HR VT 19/0600Z 38.2N 78.2W 60 KT...INLAND
72HR VT 20/0600Z 46.5N 78.5W 35 KT...INLAND EXTRATROPICAL
96HR VT 21/0600Z 57.5N 69.5W 30 KT...INLAND EXTRATROPICAL
120HR VT 22/0600Z...MERGED WITH EXTRATROPICAL LOW

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HURRICANE ISABEL DISCUSSION NUMBER 46
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
11 AM EDT WED SEP 17 2003

ALTHOUGH PEAK FLIGHT-LEVEL WINDS REMAIN BETWEEN 100 AND 105
KT...WHICH WOULD NORMALLY SUPPORT SURFACE WINDS OF ABOUT 95
KT...DROPSONDE OBSERVATIONS INDICATE THAT A LESS THAN TYPICAL
AMOUNT OF THIS WIND IS MAKING IT DOWN TO THE SURFACE LAYER. THIS
IS CONSISTENT WITH THE RELATIVELY WEAK CONVECTION IN THE INNER CORE
OF ISABEL. IN ALL LIKELIHOOD THE SURFACE WINDS ARE CLOSER TO 85
KT. I HAVE KEPT THE ADVISORY WINDS AT 95 KT FOR NOW...SINCE ANY
INCREASE IN CONVECTION WOULD MORE EFFECTIVELY TRANSPORT THE
MOMENTUM ALOFT DOWNWARD...BUT IF THE CONVECTION DOES NOT STRENGTHEN
THE INTENSITY WILL LIKELY BE LOWERED A BIT THIS AFTERNOON. EITHER
WAY ISABEL IS A CATEGORY TWO HURRICANE.

THE INITIAL MOTION REMAINS 335/8. THERE HAS BEEN NO SIGNIFICANT
CHANGE IN THE OFFICIAL FORECAST TRACK...ALTHOUGH THE MODEL GUIDANCE
HAS SHIFTED ITS LANDFALL POINT A FEW MILES TO THE WEST. THE GFDL
ADJUSTMENT WAS THE LARGEST...ABOUT 30 MILES...AND IT IS RATHER
AMAZING THAT THIS IS ABOUT THE BIGGEST ADJUSTMENT WE HAVE SEEN OVER
THE PAST COUPLE OF DAYS.

WHILE A MORE FAVORABLE UPPER PATTERN IS BEGINNING TO DEVELOP AS
FORECAST BY THE GLOBAL MODELS...THE LOW-LEVEL ENVIRONMENTAL
THERMODYNAMICS AND CURRENT STORM STRUCTURE ARE EXPECTED TO LIMIT
THE ABILITY OF ISABEL TO RESPOND TO THE UPPER FORCING. LITTLE
CHANGE IN STRENGTH IS EXPECTED PRIOR TO LANDFALL. HOWEVER...
INTENSITY FORECASTS TEND TO BE LESS CERTAIN THAN TRACK FORECASTS...
AND AN INTENSITY FORECAST ERROR OF ONE SAFFIR-SIMPSON CATEGORY...UP
OR DOWN...WOULD BE ENTIRELY POSSIBLE.

FORECASTER FRANKLIN

FORECAST POSITIONS AND MAX WINDS

INITIAL 17/1500Z 30.0N 72.6W 95 KT
12HR VT 18/0000Z 31.4N 73.5W 95 KT
24HR VT 18/1200Z 33.6N 75.4W 95 KT
36HR VT 19/0000Z 36.0N 77.3W 70 KT...INLAND
48HR VT 19/1200Z 39.0N 79.0W 50 KT...INLAND
72HR VT 20/1200Z 49.0N 77.0W 30 KT...EXTRATROPICAL
96HR VT 21/1200Z 58.0N 70.0W 25 KT...EXTRATROPICAL
120HR VT 22/1200Z...ABSORBED BY EXTRATROPICAL LOW

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HURRICANE ISABEL DISCUSSION NUMBER 47
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
5 PM EDT WED SEP 17 2003

IF FLIGHT-LEVEL OBSERVATIONS WERE ALL WE HAD...ISABEL WOULD BE A
CATEGORY THREE HURRICANE. THE HURRICANE HUNTER AIRCRAFT THIS
AFTERNOON FOUND A NUMBER OF SPOTS OF WINDS OF 110-120 KT. THIS
WOULD NORMALLY CORRESPOND TO SURFACE WINDS OF 100-105 KT.
HOWEVER...NUMEROUS DROPSONDE PROFILES IN THE HIGH WIND REGIONS OF
THE CIRCULATION SHOW A CONSISTENT AND UNUSUALLY STEEP FALL-OFF OF
WIND IN THE BOUNDARY LAYER. THIS IS CONSISTENT WITH THE MEAGER
CONVECTION IN THE HURRICANE CORE. BASED ON THESE PROFILES...THE
INITIAL INTENSITY IS SET AT 90 KT. THE UPPER-LEVEL OUTFLOW PATTERN
HAS BECOME FAVORABLE...AS WAS FORECAST BY THE GLOBAL MODELS...AND
IN FACT THE CIRCULATION ALOFT IS STRENGTHENING. HOWEVER...
THERMODYANAMIC FACTORS ARE LIMITING THE ABILITY OF ISABEL TO
COMPLETELY RESPOND TO THE FAVORABLE UPPER-LEVEL FORCING. THE
OFFICIAL FORECAST DOES NOT ANTICIPATE ANY SIGNIFICANT INCREASE IN
STRENGTH PRIOR TO LANDFALL...BUT SHOULD THERE BE A SUBSTANTIAL
INCREASE IN DEEP CONVECTION ISABEL COULD QUICKLY REACH CATEGORY
THREE STATUS.

ONCE AGAIN...THERE HAS BEEN NO SIGNIFICANT CHANGE TO THE TRACK
FORECAST OR REASONING. THE LATEST RUN OF THE GFS IS A LITTLE
FASTER AND SLIGHTLY TO THE RIGHT OF THE PREVIOUS RUN...BUT THE
GUIDANCE REMAINS IN EXCELLENT AGREEMENT. THE INITIAL MOTION IS NOW
330/12 AS ISABEL BEGINS A MODEST ACCELERATION TOWARD THE COAST.
SOME ADDITIONAL ACCELERATION IS STILL EXPECTED PRIOR TO LANDFALL.

ISABEL HAS A LARGE CIRCULATION...INCLUDING A LARGE EXTENT OF
DAMAGING WINDS. THEREFORE...IT IS ESPECIALLY IMPORTANT NOT TO
FOCUS ON THE PRECISE LANDFALL LOCATION...SINCE SIGNIFICANT IMPACTS
WILL BE FELT AT LARGE DISTANCES FROM THE LANDFALL POINT.

FORECASTER FRANKLIN

FORECAST POSITIONS AND MAX WINDS

INITIAL 17/2100Z 31.1N 73.3W 90 KT
12HR VT 18/0600Z 32.7N 74.4W 95 KT
24HR VT 18/1800Z 35.0N 76.6W 95 KT...INLAND
36HR VT 19/0600Z 37.6N 78.5W 60 KT...INLAND
48HR VT 19/1800Z 41.5N 79.0W 40 KT...INLAND
72HR VT 20/1800Z 52.5N 76.0W 30 KT...EXTRATROPICAL
96HR VT 21/1800Z...ABSORBED BY EXTRATROPICAL LOW
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Sciencerocks
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Re: Hurricane Isabel

#12 Postby Sciencerocks » Sat May 20, 2023 7:23 pm

HURRICANE ISABEL DISCUSSION NUMBER 48
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
11 PM EDT WED SEP 17 2003

ISABEL LACKS A WELL-DEFINED INNER CORE AND DEEP CONVECTION IS
MINIMAL AT THIS TIME. IN FACT...SATELLITE INTENSITY ESTIMATES
SUGGEST THAT MAXIMUM WINDS ARE ON THE ORDER OF 75 TO 80 KNOTS.
DATA FROM A RECONNAISSANCE PLANE INDICATE THAT MAXIMUM FLIGHT-LEVEL
WINDS ARE ABOUT 100 KNOTS SO FAR ON THIS MISSION...WITH THE CENTRAL
PRESSURE UNCHANGED. ASSUMING THAT THE RECONNAISSANCE PLANE HAS NOT
SAMPLED THE ENTIRE CIRCULATION...THE INITIAL INTENSITY IS KEPT
GENEROUSLY AT 90 KNOTS. IF THE PLANE DOES NOT FIND HIGHER WINDS
SOON...IT MAY BE NECESSARY TO DECREASE THE INTENSITY IN THE NEXT
ADVISORY. ON THE OTHER HAND...SINCE THE OUTFLOW IS EXCELLENT AND
THE HURRICANE HAS ABOUT 12 HOURS OVER WARM WATERS...THERE IS STILL
A CHANCE THAT SOME RE-INTENSIFICATION MAY OCCUR JUST BEFORE
LANDFALL.

SATELLITE AND RECONNAISSANCE FIXES INDICATE THAT ISABEL IS MOVING
ABOUT 330 DEGREES AT 11 KNOTS. THE STEERING PATTERN CALLS FOR
A GENERAL NORTH-NORTHWESTWARD TO NORTHWESTWARD TRACK AS THE HIGH
BUILDS TO THE NORTHEAST OF THE TROPICAL CYCLONE. THIS MOTION WOULD
BRING THE CENTER OF THE HURRICANE TO THE COAST OF NORTH CAROLINA
DURING THE DAY ON THURSDAY. THERE IS CONFIDENCE IN THE OFFICIAL
FORECAST SINCE THE MORE RELIABLE TRACK MODELS ARE HIGHLY CLUSTERED
WITHIN 40 NAUTICAL MILES NEAR LANDFALL. HOWEVER...ONE SHOULD NOT
FOCUS ON A PRECISE LANDFALL POINT SINCE ISABEL IS A LARGE HURRICANE
WITH DAMAGING WINDS EXTENDING WELL AWAY FROM THE CENTER.

ONCE ISABEL MOVES INLAND...IT SHOULD GRADUALLY BECOME EXTRATROPICAL
AND THEN BECOME ABSORBED BY A LARGER CYCLONE IN 3 OR 4 DAYS.

FORECASTER AVILA/PASCH

FORECAST POSITIONS AND MAX WINDS

INITIAL 18/0300Z 31.9N 73.9W 90 KT
12HR VT 18/1200Z 33.7N 75.6W 95 KT
24HR VT 19/0000Z 36.5N 77.5W 65 KT...INLAND
36HR VT 19/1200Z 39.5N 78.5W 50 KT...INLAND
48HR VT 20/0000Z 43.0N 77.5W 40 KT...BECOMING EXTRATROPICAL
72HR VT 21/0000Z 57.0N 73.5W 30 KT...EXTRATROPICAL
96HR VT 22/0000Z...ABSORBED BY EXTRATROPICAL LOW


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https://www.youtube.com/watch?v=dIAacac3uRc
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HURRICANE ISABEL DISCUSSION NUMBER 49
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
5 AM EDT THU SEP 18 2003

WSR-88D RADAR DATA FROM MOREHEAD CITY SHOWS WHAT LOOKS LIKE A
CLASSIC CONCENTRIC EYEWALL FORMATION...WITH A POORLY-DEFINED RING
OF CONVECTION NEAR THE CENTER AND A STRONGER RING 40-50 NM OUT.
EARLIER AIRCRAFT DATA INDICATES THAT THE STRONGEST WINDS ARE
ASSOCIATED WITH THE OUTER RING...AND THAT THERE IS NO WIND MAXIMUM
ASSOCIATED WITH THE INNER RING. THE LAST AIRCRAFT FIX SHOWED A
PRESSURE OF 957 MB...AND MAXIMUM FLIGHT LEVEL WINDS DURING THE
MISSION WERE 109 KT. THE INITIAL INTENSITY REMAINS 90 KT.

ISABEL IS MOVING 325-330 DEGREES AT ABOUT 12 KT. A GENERAL
NORTHWESTWARD MOTION SHOULD CONTINUE FOR ABOUT 24 HR BETWEEN THE
DEVELOPING MID/UPPER-LEVEL TROUGH OVER THE SOUTHEASTERN UNITED
STATES AND THE DEEP-LAYER RIDGE OVER THE NORTHWESTERN ATLANTIC.
AFTER THAT...ISABEL SHOULD TURN NORTHWARD IN RESPONSE TO THE LARGE
DEEP-LAYER TROUGH MOVING EASTWARD ACROSS THE NORTHERN UNITED
STATES. ALL DYNAMICAL GUIDANCE AGREES WITH THIS SCENARIO...AND THE
OFFICIAL FORECAST TRACK IS BASICALLY AN UPDATE OF THE PREVIOUS
PACKAGE.

LITTLE CHANGE IN STRENGTH IS FORECAST BEFORE LANDFALL...ALTHOUGH
THERE IS STILL A SLIGHT CHANCE OF SLIGHT STRENGTHENING. AFTER
LANDFALL...ISABEL SHOULD WEAKEN AND GRADUALLY BECOME EXTRATROPICAL.

A NEW AIRCRAFT SHOULD BE ARRIVING AT THE CENTER SHORTLY.

FORECASTER BEVEN

FORECAST POSITIONS AND MAX WINDS

INITIAL 18/0900Z 33.1N 74.7W 90 KT
12HR VT 18/1800Z 35.0N 76.4W 90 KT...INLAND
24HR VT 19/0600Z 37.9N 78.2W 60 KT...INLAND
36HR VT 19/1800Z 41.4N 78.5W 45 KT...BECOMING EXTRATROPICAL
48HR VT 20/0600Z 47.0N 78.0W 35 KT...INLAND EXTRATROPICAL
72HR VT 21/0600Z 59.5N 72.5W 30 KT...INLAND EXTRATROPICAL
96HR VT 22/0600Z...ABSORBED BY EXTRATROPICAL LOW

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HURRICANE ISABEL DISCUSSION NUMBER 50
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
11 AM EDT THU SEP 18 2003

THE LARGE EYEWALL OF ISABEL IS COMING ASHORE ALONG THE NORTH
CAROLINA OUTER BANKS. ALTHOUGH AIRCRAFT RECONNAISSANCE REPORTS
FLIGHT-LEVEL WINDS OF 111 KT...SURFACE WINDS ARE ESTIMATED TO BE
SUBSTATIALLY LOWER...ABOUT 85 KT. LITTLE CHANGE IN STRENGTH IS
EXPECTED PRIOR TO THE CENTER MAKING LANDFALL. ALTHOUGH ISABEL WILL
WEAKEN AFTER LANDFALL...THE STRONG WINDS ALOFT WILL BE FELT IN THE
FORM OF HURRICANE FORCE WIND GUSTS WELL INLAND OVER THE ELEVATED
TERRAIN OF NORTHERN VIRGINIA AND WESTERN MARYLAND...AS WELL AS ON
HIGH RISE BUILDINGS AND OTHER STRUCTURES IN MAJOR METROPOLITAN
AREAS NEAR AND ESPECIALLY EAST OF THE PATH OF ISABEL.

THERE HAS BEEN LITTLE CHANGE TO THE FORECAST TRACK. ISABEL IS
EXPECTED TO BECOME EXTRATROPICAL WITHIN 36 HOURS AND BE ABSORBED
AFTER 48 HOURS.

FORECASTER FRANKLIN

FORECAST POSITIONS AND MAX WINDS

INITIAL 18/1500Z 34.4N 75.7W 85 KT
12HR VT 19/0000Z 36.5N 77.3W 65 KT...INLAND
24HR VT 19/1200Z 39.7N 78.7W 45 KT...INLAND
36HR VT 20/0000Z 44.5N 78.7W 30 KT...EXTRATROPICAL
48HR VT 20/1200Z 50.5N 77.0W 30 KT...EXTRATROPICAL
72HR VT 21/1200Z...ABSORBED BY EXTRATROPICAL LOW


NNNN
https://www.youtube.com/watch?v=vN4iy21AZzw

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HURRICANE ISABEL DISCUSSION NUMBER 51
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
5 PM EDT THU SEP 18 2003

ISABEL MADE LANDFALL ON THE OUTER BANKS OF NORTH CAROLINA NEAR DRUM
INLET...BETWEEN CAPE LOOKOUT AND OCRACOKE ISLAND...NEAR 17Z THIS
AFTERNOON...WITH WINDS ESTIMATED NEAR 85 KT. A GPS DROPSONDE
REPORTED SURFACE WINDS OF 83 KT ABOUT AN HOUR BEFORE LANDFALL A FEW
MILES FROM CAPE HATTERAS IN THE NORTHEAST EYEWALL. THE STEPPED
FREQUENCY MICROWAVE RADIOMETER ON BOARD THE NOAA P-3 AIRCRAFT
REPORTED SURFACE WINDS OF 90 KT AT 1707Z IN THE SAME AREA...AND
ANOTHER MEASUREMENT OF 82 KT WAS REPORTED ABOUT AN HOUR EARLIER.
RECONNAISSANCE AIRCRAFT MEASURED PEAK FLIGHT-LEVEL WINDS OF 118 KT.
THE AIRCRAFT MEASUREMENTS WERE CONFIRMED BY GROUND-BASED DOPPLER
RADARS. A LARGE NUMBER OF DROPSONDES IN ISABEL INDICATE THAT
SURFACE WINDS WERE AVERAGING ABOUT 70% OF THE FLIGHT-LEVEL VALUES
OVER THE LAST DAY OR TWO...AND THIS ALSO YIELDS ABOUT 83 KT FOR A
PEAK SURFACE WIND ESTIMATE.

ISABEL CONTINUES INLAND...AND WHILE THERE HAS BEEN SOME SHARPENING
UP OF THE EYEWALL AFTER LANDFALL...THE MAXIMUM WINDS SHOULD BE
DECREASING. GIVEN THE PRESENT ORGANIZATION OF THE CORE AND THE
LARGE AND STRONG CIRCULATION ALOFT...THE FORECAST DECREASE OF WIND
IS SLOWER THAN INDICATED BY THE DECAY SHIPS MODEL GUIDANCE. THE
STRONG WINDS ALOFT WILL BE FELT IN THE FORM OF HURRICANE FORCE WIND
GUSTS WELL INLAND OVER THE ELEVATED TERRAIN OF NORTHERN VIRGINIA
AND WESTERN MARYLAND...AS WELL AS ON HIGH RISE BUILDINGS AND OTHER
STRUCTURES IN MAJOR METROPOLITAN AREAS NEAR AND ESPECIALLY EAST OF
THE PATH OF ISABEL.

THERE HAS BEEN LITTLE CHANGE TO THE FORECAST TRACK. ISABEL IS
EXPECTED TO BECOME EXTRATROPICAL WITHIN 36 HOURS AND BE ABSORBED
AFTER 48 HOURS.

FORECASTER FRANKLIN

FORECAST POSITIONS AND MAX WINDS

INITIAL 18/2100Z 36.2N 77.1W 80 KT
12HR VT 19/0600Z 39.0N 78.6W 55 KT...INLAND
24HR VT 19/1800Z 43.5N 79.7W 35 KT...INLAND
36HR VT 20/0600Z 49.5N 79.6W 30 KT...EXTRATROPICAL
48HR VT 20/1800Z 55.5N 76.5W 25 KT...EXTRATROPICAL
72HR VT 21/1800Z...MERGED WITH EXTRATROPICAL LOW


NNNN
https://www.youtube.com/watch?v=e-gGHw6xULM
https://www.youtube.com/watch?v=YE1jq_QqvhU

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TROPICAL STORM ISABEL DISCUSSION NUMBER 52
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
11 PM EDT THU SEP 18 2003

RADAR...SATELLITE AND SURFACE OBSERVATIONS SUGGEST THAT ISABEL IS
RAPIDLY LOSING ITS INNER CORE AND THE CONVECTION IS WEAKENING.
INITIAL INTENSITY HAS BEEN DECREASED TO 55 KNOTS. A CONTINUED
WEAKENING IS ANTICIPATED AND ISABEL IS EXPECTED TO MERGE WITH AN
EXTRATROPICAL LOW IN ABOUT 2 DAYS OR LESS. WINDS HAVE BEGUN TO
DIMINISHED ALONG THE COAST BUT THE PRESSURE GRADIENT STILL SUPPORTS
TROPICAL STORM FORCE WINDS...PRIMARILY TO THE NORTHEAST OF THE
CENTER.

THE TROPICAL CYCLONE IS MOVING TOWARD THE NORTH-NORTHWEST ABOUT 20
KNOTS. A GRADUAL TURN TO THE NORTH WITH AN INCREASE IN FORWARD SPEED
IS EXPECTED...AS THE CYCLONE BEGINS TO BECOME EXTRATROPICAL.

FORECASTER AVILA

FORECAST POSITIONS AND MAX WINDS

INITIAL 19/0300Z 37.7N 78.0W 55 KT...INLAND
12HR VT 19/1200Z 40.5N 79.5W 40 KT...INLAND
24HR VT 20/0000Z 46.5N 79.5W 30 KT...BECOMING EXTRATROPICAL
36HR VT 20/1200Z 53.0N 79.0W 25 KT...EXTRATROPICAL
48HR VT 21/0000Z 58.5N 75.5W 25 KT...EXTRATROPICAL
72HR VT 22/0000Z...MERGED WITH EXTRATROPICAL LOW
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TROPICAL STORM ISABEL DISCUSSION NUMBER 53
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
5 AM EDT FRI SEP 19 2003

SURFACE OBSERVATION SUGGEST THE CENTRAL PRESSURE OF ISABEL HAS RISEN
CONSIDERABLY OVER THE PAST FEW HOURS. THE LOWEST PRESSURE OBSERVED
RECENTLY HAS BEEN ABOUT 991 MB IN THE STAUNTON VIRGINIA AREA. THIS
IS THE BASIS FOR THE 987 MB IN THE ADVISORY...AND EVEN THAT MIGHT
BE A STRETCH. SURFACE OBSERVATIONS FROM THE ATLANTIC COAST...
CHESAPEAKE BAY...AND DELAWARE BAY INDICATE SUSTAINED WINDS OF 35-45
KT...SO THE INITIAL INTENSITY IS LOWERED TO 45 KT. ISABEL SHOULD
CONTINUE TO WEAKEN AS IT STARTS TO LOSE TROPICAL CHARACTERISTICS
OVER THE NEXT 12-24 HR.

THE RADAR SIGNATURE HAS WEAKENED TO THE POINT THAT THE CENTER IS
HARD TO PIN DOWN. THE INITIAL MOTION IS THUS A RATHER UNCERTAIN
335/18. ISABEL SHOULD TURN NORTHWARD AND ACCELERATE IN RESPONSE TO
THE APPROACHING TROUGH OVER THE NORTH CENTRAL UNITED STATES...WITH
A GENERAL NORTHWARD MOTION PERSISTING UNTIL DISSIPATION.

FORECASTER BEVEN

FORECAST POSITIONS AND MAX WINDS

INITIAL 19/0900Z 39.2N 78.7W 45 KT...INLAND
12HR VT 19/1800Z 42.8N 79.2W 35 KT...BECOMING EXTRATROPICAL
24HR VT 20/0600Z 49.4N 79.0W 30 KT...EXTRATROPICAL
36HR VT 20/1800Z 56.0N 77.0W 25 KT...EXTRATROPICAL
48HR VT 21/0600Z 61.1N 75.0W 25 KT...EXTRATROPICAL
72HR VT 22/0600Z...ABSORBED BY EXTRATROPICAL LOW

TROPICAL DEPRESSION ISABEL DISCUSSION NUMBER 54
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
11 AM EDT FRI SEP 19 2003

ISABEL IS LOSING ITS TROPICAL CHARACTERISTICS. THERE IS NO DEEP
CONVECTION REMAINING IN THE CIRCULATION...AND THE MAXIMUM SURFACE
WINDS ARE LOCATED OVER 200 NM FROM THE CIRCULATION CENTER OVER THE
WATERS OF THE GREAT LAKES...DELAWARE BAY...AND CHESAPEAKE BAY.
THEREFORE...THIS WILL BE THE LAST ADVISORY ON ISABEL.

THE OFFICIAL TRACK AND INTENSITY FORECAST HAS BEEN COORDINATED WITH
THE CANADIAN HURRICANE CENTER. THERE IS A POSSIBILITY THAT THERE
WILL BE SOME EXTRATROPICAL RESTRENGTHENING AS ISABEL INTERACTS WITH
THE APPROACHING LARGE-SCALE MID-LEVEL TROUGH CURRENTLY IN THE
NORTHERN PLAINS.

ALTHOUGH ALL TROPICAL STORM WARNINGS HAVE BEEN DISCONTINUED...
SIGNIFICANT STORM SURGE FLOODING REMAINS. PLEASE CONSULT COASTAL
FLOOD WARNINGS AND OTHER STATEMENTS FROM LOCAL NWS FORECAST OFFICES
CONCERNING HAZARDOUS CONDITIONS IN YOUR AREA. MARINE INTERESTS
SHOULD EXERCISE CAUTION UNTIL WINDS AND SEAS SUBSIDE.

FORECASTER FRANKLIN

FORECAST POSITIONS AND MAX WINDS

INITIAL 19/1500Z 42.0N 80.7W 30 KT...BECOMING EXTRATROPICAL
12HR VT 20/0000Z 47.0N 80.5W 35 KT...EXTRATROPICAL
24HR VT 20/1200Z 54.0N 79.0W 35 KT...EXTRATROPICAL
36HR VT 21/0000Z 60.0N 77.0W 35 KT...EXTRATROPICAL
48HR VT 21/1200Z...MERGED WITH EXTRATROPICAL LOW
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