EPAC: Tropical Storm Hernan

[HURAKAN]

[Chacor]

WTPZ44 KNHC 111434
TCDEP4
HURRICANE HERNAN DISCUSSION NUMBER 20
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL EP092008
800 AM PDT MON AUG 11 2008

OVER THE PAST SIX HOURS OR SO...DEEP CONVECTION AROUND THE CENTER OF
HERNAN HAS CONTRACTED IN AREA AND THE EYE HAS CONTINUED TO FILL
WITH CLOUDS. DVORAK DATA T-NUMBERS ARE 4.0 AND 4.5 FROM TAFB AND
SAB... RESPECTIVELY...SO THE INITIAL INTENSITY WILL BE MAINTAINED
AT 70 KT AS A CONSENSUS OF THESE NUMBERS. HERNAN IS NOW OVER COOL
SEA SURFACE TEMPERATURES NEAR 24C BUT THE POWERFUL CIRCULATION HAS
CAUSED THE SYSTEM TO BE SOMEWHAT RESISTANT TO A RAPID DECAY. IN
ADDITION...THE FORECAST TRACK TAKES HERNAN WEST-SOUTHWEST PARALLEL
TO THE STRONG SST GRADIENT SO ONLY GRADUAL WEAKENING IS FORECAST
OVER THE NEXT 48 HOURS IN LINE WITH SHIPS AND THE INTENSITY
CONSENSUS. THERE IS A POSSIBILITY THAT HERNAN COULD MAINTAIN
TROPICAL CYCLONE STATUS THROUGH DAYS 4 AND 5 EVEN THOUGH THE
OFFICIAL FORECAST CALLS FOR WEAKENING TO A REMNANT LOW.

HERNAN HAS BEEN ON A SHORT-TERM TRACK JUST SLIGHTLY NORTH OF THE
PREVIOUS FORECAST WITH AN INITIAL MOTION OF 285/9. HERNAN IS
APPROACHING A MIDDLE TO UPPER-LEVEL TROUGH NORTHEAST OF HAWAII AND
IS LOCATED NEAR AN AREA OF LOW PRESSURE NEAR 16N143W...BOTH OF
WHICH MAY BE CONTRIBUTING TO THE RECENT NORTHWESTWARD MOTION. ONCE
THE CYCLONE BEGINS ITS WEAKENING TREND...A SOUTHWESTWARD TURN IS
EXPECTED TO COMMENCE AS THE CIRCULATION IS STEERED BY THE LOW-LEVEL
RIDGE. HERNAN IS EXPECTED TO CROSS INTO THE CENTRAL PACIFIC BASIN
SOMETIME ON THURSDAY.

WIND RADII HAVE BEEN CONTRACTED BASED ON AN EXCELLENT 0620 UTC ASCAT
PASS COVERING MOST OF HERNAN'S CIRCULATION.


FORECAST POSITIONS AND MAX WINDS

INITIAL 11/1500Z 19.0N 130.2W 70 KT
12HR VT 12/0000Z 19.0N 131.2W 60 KT
24HR VT 12/1200Z 18.6N 132.7W 50 KT
36HR VT 13/0000Z 18.2N 134.2W 40 KT
48HR VT 13/1200Z 17.7N 135.7W 35 KT
72HR VT 14/1200Z 16.5N 139.0W 30 KT
96HR VT 15/1200Z 15.5N 143.0W 25 KT...REMNANT LOW
120HR VT 16/1200Z 15.5N 147.0W 25 KT...REMNANT LOW

$$
FORECASTER BERG/PASCH

[HurricaneRobert]

This is a tropical storm now. The clouds just ahead make it look like its in cool water.

[Chacor]

Looks like everyone focused on 93L and 92L missed the news.

087
WTPZ44 KNHC 112030
TCDEP4
TROPICAL STORM HERNAN DISCUSSION NUMBER 21
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL EP092008
200 PM PDT MON AUG 11 2008

HERNAN WAS DIAGNOSED AS A MARGINAL HURRICANE AT THE 18Z SYNOPTIC
TIME...BUT SINCE THEN THE LOW-LEVEL AND UPPER-LEVEL CIRCULATIONS
HAVE STARTED TO DECOUPLE. BASED ON THIS MOST RECENT SATELLITE
TREND...HERNAN HAS BEEN DOWNGRADED TO A 60-KT TROPICAL STORM AT THE
21Z ADVISORY TIME.

NOW THAT THE LOW- TO MID-LEVEL CIRCULATIONS HAVE STARTED TO DECOUPLE
FROM THE UPPER-LEVEL CIRCULATION...HERNAN IS EXPECTED TO MAKE MORE
OF A WESTWARD AND WEST-SOUTHWESTWARD MOTION AS IT COMES UNDER THE
INFLUENCE OF THE STRONG LOW-LEVEL RIDGING TO THE NORTH OF THE
CYCLONE. THIS FORECAST SCENARIO IS CONSISTENT WITH THE CONSENSUS OF
ALL OF THE NHC MODELS. HERNAN OR ITS REMNANT CIRCULATION IS
EXPECTED TO CROSS INTO THE CENTRAL PACIFIC BASIN ON THURSDAY.

HERNAN WILL BE PASSING OVER SUB-24C SEA SURFACE TEMPERATURES FOR THE
NEXT 48 HOURS...WHICH SHOULD INDUCE CONTINUED WEAKENING. HOWEVER...
BY 72 HOURS...THE CYCLONE WILL BE MOVING OVER 25C AND WARMER SSTS
AND ALSO BE UNDER THE INFLUENCE OF LIGHT SOUTHEASTERLY UPPER-LEVEL
SHEAR...WHICH COULD ALLOW FOR SOME REDEVELOPMENT OF CONVECTION THAT
WOULD HELP MAINTAIN THE SYSTEM AS A TROPICAL CYCLONE RATHER THAN A
REMNANT LOW AT DAYS 4 AND 5.

FORECAST POSITIONS AND MAX WINDS

INITIAL 11/2100Z 19.0N 131.2W 60 KT
12HR VT 12/0600Z 18.9N 132.3W 55 KT
24HR VT 12/1800Z 18.5N 133.9W 45 KT
36HR VT 13/0600Z 18.0N 135.4W 40 KT
48HR VT 13/1800Z 17.6N 137.2W 35 KT
72HR VT 14/1800Z 16.5N 140.5W 30 KT
96HR VT 15/1800Z 16.0N 144.5W 25 KT...REMNANT LOW
120HR VT 16/1800Z 16.0N 148.5W 25 KT...REMNANT LOW

$$
FORECASTER STEWART/PASCH


Stacy Stewart's back.

[Chacor]

191
WTPZ44 KNHC 120228
TCDEP4
TROPICAL STORM HERNAN DISCUSSION NUMBER 22
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL EP092008
800 PM PDT MON AUG 11 2008

CONVECTION CONTINUES TO SLOWLY DECREASE NEAR THE CENTER OF THE
CYCLONE. IN ADDITION...MICROWAVE IMAGES SUGGEST THE LOW-LEVEL
CIRCULATION OF HERNAN APPEARS TO BE DETACHED SOMEWHAT TO THE
SOUTHEAST OF THE HIGHER-LEVEL CIRCULATION. IN ACCORDANCE WITH
SATELLITE ESTIMATES...THE INITIAL INTENSITY IS LOWERED TO 55 KT.
ALL SIGNS POINT TO A CONTINUED WEAKENING OF HERNAN...WITH COLD
WATER AND STABLE AIR IN ITS FUTURE. THE OFFICIAL FORECAST IS CLOSE
TO THE LGEM MODEL...WHICH HAS VERIFIED WELL IN THE PAST FOR EASTERN
PACIFIC SYSTEMS DISSIPATING OVER COOL WATERS. MOST OF THE MODEL
GUIDANCE SUGGESTS THIS SYSTEM WILL BECOME A REMNANT LOW IN ABOUT
THREE DAYS...OR SOONER.

HERNAN APPEARS TO HAVE TURNED DUE WEST AT ABOUT 8 KT TONIGHT.
GUIDANCE IS IN GOOD AGREEMENT ON A WEST-SOUTHWESTWARD MOTION
TOMORROW AS STEERING CURRENTS BECOME DOMINATED BY STRONG LOW-LEVEL
RIDGING TO THE NORTH OF THE TROPICAL CYCLONE. THIS FORECAST
SCENARIO IS CONSISTENT WITH THE DYNAMICAL MODEL CONSENSUS AND THE
LATEST FORECAST IS JUST A LITTLE SOUTH OF THE PREVIOUS FORECAST.
HERNAN OR ITS REMNANT CIRCULATION IS EXPECTED TO CROSS INTO THE
CENTRAL PACIFIC BASIN ON THURSDAY.


FORECAST POSITIONS AND MAX WINDS

INITIAL 12/0300Z 18.9N 131.7W 55 KT
12HR VT 12/1200Z 18.7N 132.9W 45 KT
24HR VT 13/0000Z 18.3N 134.5W 40 KT
36HR VT 13/1200Z 17.8N 136.1W 35 KT
48HR VT 14/0000Z 17.2N 137.6W 30 KT...DISSIPATING
72HR VT 15/0000Z 16.0N 141.3W 25 KT...REMNANT LOW
96HR VT 16/0000Z 15.5N 145.5W 25 KT...REMNANT LOW
120HR VT 17/0000Z 15.5N 149.5W 20 KT...REMNANT LOW

$$
FORECASTER BLAKE

[Chacor]

WTPZ44 KNHC 121444
TCDEP4
TROPICAL STORM HERNAN DISCUSSION NUMBER 24
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL EP092008
800 AM PDT TUE AUG 12 2008

HERNAN HAS VERY LITTLE DEEP CONVECTION NOW THAT IT IS OVER SEA
SURFACE TEMPERATURES NEAR 23C. AN AVERAGE OF THE TAFB AND SAB
SATELLITE CLASSIFICATIONS PROVIDES AN ESTIMATE OF 45 KT AND THE
MOST RECENT ADT IS NOW DOWN TO 30 KT. GIVEN THE DEGRADATION OF THE
CLOUD PATTERN...THE INITIAL INTENSITY IS SET AS 40 KT AS A
COMPROMISE OF THE SUBJECTIVE AND OBJECTIVE TECHNIQUES. SINCE IT IS
UNLIKELY THAT HERNAN WILL BE ABLE TO GENERATE PERSISTENT CONVECTION
OVER THE COOLER WATERS...THE CYCLONE IS EXPECTED TO WEAKEN TO A
TROPICAL DEPRESSION LATER TODAY. THE NEW FORECAST SHOWS HERNAN
DISSIPATING INTO AN OPEN WAVE WITHIN THE TRADE WIND BELT SOUTHEAST
OF HAWAII BY DAY 5...IF NOT SOONER...IN LINE WITH THE GLOBAL MODEL
GUIDANCE.

THE INITIAL MOTION IS JUST SOUTH OF DUE WEST AT 260/8. THE
SHORT-TERM MOTION WILL BE DICTATED BY A MID-LEVEL RIDGE AXIS
EXTENDING SOUTHWEST OF SOUTHERN CALIFORNIA DIRECTLY TOWARDS
HERNAN...WHICH WILL FORCE A MORE WEST-SOUTHWESTWARD MOTION. ONCE
HERNAN WEAKENS TO A REMNANT LOW...IT IS EXPECTED TO TURN WEST WITH
AN INCREASE IN SPEED AS IT IS STEERED BY THE LOW-LEVEL SUBTROPICAL
RIDGE.


FORECAST POSITIONS AND MAX WINDS

INITIAL 12/1500Z 18.3N 133.6W 40 KT
12HR VT 13/0000Z 18.1N 134.7W 30 KT
24HR VT 13/1200Z 17.7N 136.2W 30 KT
36HR VT 14/0000Z 17.2N 137.7W 25 KT...REMNANT LOW
48HR VT 14/1200Z 16.7N 139.2W 25 KT...REMNANT LOW
72HR VT 15/1200Z 15.5N 143.5W 20 KT...REMNANT LOW
96HR VT 16/1200Z 15.0N 148.0W 20 KT...REMNANT LOW
120HR VT 17/1200Z...DISSIPATED

$$
FORECASTER BERG/BROWN

[RL3AO]

TROPICAL DEPRESSION HERNAN DISCUSSION NUMBER 26
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL EP092008
800 PM PDT TUE AUG 12 2008

ALL THAT REMAINS OF THE ONCE-POWERFUL TROPICAL CYCLONE IS A TIGHT
LOW-LEVEL CIRCULATION. DEEP THUNDERSTORM ACTIVITY HAS BEEN ABSENT
FOR ABOUT 18 HOURS NEAR THE CENTER...AND HERNAN NO LONGER MEETS THE
DEFINITION OF A TROPICAL CYCLONE. INITIAL INTENSITY IS LOWERED TO
30 KT IN GOOD AGREEMENT WITH SATELLITE ESTIMATES. A SLOW WEAKENING
OF THE CIRCULATION IS LIKELY UNTIL TOTAL DISSIPATION IN ABOUT FOUR
DAYS.

HERNAN IS MOVING TOWARD WEST-SOUTHWEST AT ABOUT 7 KT. THIS GENERAL
MOTION IS EXPECTED FOR THE NEXT COUPLE OF DAYS WITH A SMALL BEND TO
THE WEST IN THE LONGER-TERM AS THE RIDGE WEAKENS TO THE NORTH OF
THE LOW.

THIS IS THE LAST ADVISORY ON HERNAN ISSUED BY THE NATIONAL HURRICANE
CENTER. FUTURE INFORMATION ON THIS SYSTEM CAN BE FOUND IN HIGH SEAS
FORECASTS ISSUED BY THE NATIONAL WEATHER SERVICE...UNDER AWIPS
HEADER NFDHSFEPI AND WMO HEADER FZPN02 KWBC.


FORECAST POSITIONS AND MAX WINDS

INITIAL 13/0300Z 18.2N 134.8W 30 KT...REMNANT LOW
12HR VT 13/1200Z 17.9N 135.8W 25 KT...REMNANT LOW
24HR VT 14/0000Z 17.5N 137.2W 25 KT...REMNANT LOW
36HR VT 14/1200Z 16.9N 138.7W 20 KT...REMNANT LOW
48HR VT 15/0000Z 16.4N 140.6W 20 KT...REMNANT LOW
72HR VT 16/0000Z 15.5N 144.5W 20 KT...REMNANT LOW
96HR VT 17/0000Z...DISSIPATED

$$
FORECASTER BLAKE