EPAC: HILDA- Post-Tropical

[Kingarabian]

Crap ton of dry air to the NW. Although it seems to be shielding itself. Shear still seems minimal despite CIMSS showing 20kts of shear over it and 30kts of shear soon.

[Kingarabian]

Cphc went with 85kts. Should've been 90kts.

[Kingarabian]

06z GFS has it moving due west after 24 hours safely missing the big Island to the south.

[tolakram]

Live IR

http://wwwghcc.msfc.nasa.gov/cgi-bin/get-goes?satellite=GOES-W%20PACUS&lat=16&lon=-150&info=ir&zoom=1&width=1000&height=800&type=Animation&quality=95&palette=ir1.pal&numframes=20

[Kingarabian]

Looks like it's doing a great job in pushing away that dry air.

[Kingarabian]

WTPA45 PHFO 100903
TCDCP5

HURRICANE HILDA DISCUSSION NUMBER 18
NWS CENTRAL PACIFIC HURRICANE CENTER HONOLULU HI EP102015
1100 PM HST SUN AUG 09 2015

THE FIRST RECONNAISSANCE FLIGHT INTO HILDA WAS CONDUCTED BY THE
U.S. 53RD WEATHER RECONNAISSANCE SQUADRON EARLIER THIS EVENING...
WITH ANOTHER MISSION SCHEDULED FOR MONDAY MORNING. THE AIRCRAFT DATA
CONFIRM THAT HILDA IS A VERY SMALL SYSTEM...AND BASED ON A BLEND OF
THE FLIGHT LEVEL...DROPSONDE AND SFMR WINDS...THE INITIAL INTENSITY
FOR THIS ADVISORY IS DETERMINED TO BE 85 KT. THE HURRICANE HUNTERS
NOTED THAT THE EYE WAS EVOLVING IN SHAPE AND SIZE...WITH BREAKS IN
THE EYE WALL APPARENT. GRADUALLY INCREASING CENTRAL PRESSURE LEADS
TO THE CONCLUSION THAT HILDA IS ON A WEAKENING TREND.

THE TRACK AND INTENSITY FORECASTS FOR HILDA REMAIN INTRICATELY
LINKED AS THE CYCLONE INTERACTS WITH AN INCREASINGLY HOSTILE
ENVIRONMENTAL WIND PROFILE. IF HILDA WERE TO REMAIN A STRONG AND
DEEP SYSTEM...IT WOULD BE INFLUENCED BY STEERING FLOW THROUGH A
DEEPER LAYER OF THE ATMOSPHERE...WHICH WOULD RESULT IN A MORE
NORTHERLY TRACK. THE WEAKER AND SHALLOWER HILDA BECOMES...THE MORE
ITS TRACK WILL BE INFLUENCED BY THE LOW-LEVEL TRADE WIND FLOW...
RESULTING IN A MORE WESTERLY TRACK. THE OFFICIAL FORECAST ASSUMES A
FAIRLY DEEP SYSTEM INITIALLY WILL BECOME INCREASINGLY SHALLOW
THROUGH THE FORECAST PERIOD.

THE CURRENT MOTION ESTIMATE IS 300/08 KT...AS HILDA IS ROUNDING THE
WESTERN EDGE OF A DEEP LAYER RIDGE CENTERED TO THE DISTANT
EAST-NORTHEAST. HILDA WILL CONTINUE TO GAIN LATITUDE OVER THE NEXT
COUPLE OF DAYS AS IT GRADUALLY ROUNDS THE RIDGE. AS IT DOES SO...
HILDA WILL BEGIN TO FEEL THE EFFECTS OF INCREASING WESTERLY WINDS
ALOFT...ASSOCIATED WITH THE SUBTROPICAL JET STREAM THAT IS BEING
ENHANCED BY A LOW ALOFT CENTERED NORTH OF HAWAII. THE FORWARD
MOTION OF THE CYCLONE IS FORECAST TO DIMINISH SIGNIFICANTLY OVER
THE NEXT 48 HOURS AS THE STEERING FLOW WEAKENS...AND THE LOWER AND
UPPER LEVELS OF THE SYSTEM GRADUALLY DECOUPLE. IN THE LATER
PERIODS...SHEAR WILL REMAIN HIGH...AND THE FORECAST ANTICIPATES THAT
A MUCH WEAKER HILDA WILL BEGIN TO MOVE TOWARD THE WEST-NORTHWEST
WITH A GRADUAL INCREASE IN FORWARD SPEED.

THE OFFICIAL TRACK FORECAST IS CLOSE TO THE PREVIOUS...BUT HAS
BEEN NUDGED TOWARD THE TVCN CONSENSUS. THE TRACK FORECAST THUS
WAS NUDGED A LITTLE TO THE LEFT INITIALLY...AND A LITTLE TO THE
RIGHT ON DAYS 4 AND 5...IN RESPONSE TO A SHIFT SEEN IN THE LATEST
ECMWF GUIDANCE. THE INTENSITY FORECAST IS SIMILAR TO THE PREVIOUS...
AND CLOSELY FOLLOWS THE IVCN CONSENSUS. THE FORECAST ANTICIPATES
THAT HILDA WILL WEAKEN TO A TROPICAL STORM ON TUESDAY.


FORECAST POSITIONS AND MAX WINDS

INIT 10/0900Z 15.7N 149.1W 85 KT 100 MPH
12H 10/1800Z 16.3N 150.1W 75 KT 85 MPH
24H 11/0600Z 17.0N 151.0W 65 KT 75 MPH
36H 11/1800Z 17.6N 151.7W 55 KT 65 MPH
48H 12/0600Z 18.1N 152.1W 50 KT 60 MPH
72H 13/0600Z 18.8N 153.1W 35 KT 40 MPH
96H 14/0600Z 19.3N 155.0W 30 KT 35 MPH
120H 15/0600Z 20.0N 158.0W 25 KT 30 MPH

$$

FORECASTER BIRCHARD

[TheStormExpert]

This might be a silly question but why is there always a wall of strong wind shear over or around Hawaii?

[cycloneye]

HURRICANE HILDA DISCUSSION NUMBER 19
NWS CENTRAL PACIFIC HURRICANE CENTER HONOLULU HI EP102015
500 AM HST MON AUG 10 2015

LATEST SUBJECTIVE AND OBJECTIVE DVORAK SATELLITE INTENSITY
ESTIMATES RANGE FROM 4.5/77 KT TO 5.0/90 KT. GIVEN THE FACT THAT
HILDA/S SATELLITE REPRESENTATION HAS DEGRADED ONLY MARGINALLY
OVER THE PAST 6 HOURS...THE INITIAL INTENSITY FOR THIS ADVISORY HAS
BEEN LOWERED SLIGHTLY TO 80 KT. ANOTHER FLIGHT INTO HILDA WILL BE
CONDUCTED BY THE U.S. 53RD WEATHER RECONNAISSANCE SQUADRON LATER
THIS MORNING.

THE INITIAL MOTION VECTOR FOR THIS ADVISORY IS 300/08 KT...AS HILDA
CONTINUES TO ROUND THE WESTERN EDGE OF A DEEP LAYER RIDGE CENTERED
TO THE DISTANT EAST. HILDA IS EXPECTED TO GAIN LATITUDE OVER THE
NEXT COUPLE OF DAYS AS IT ROUNDS THE RIDGE...BUT THE FORWARD SPEED
IS FORECAST TO DIMINISH AS THE STEERING FLOW WEAKENS TODAY AND
TOMORROW. AS HILDA MOVES NORTH OF THE RIDGE AXIS...IT WILL ENCOUNTER
INCREASING WESTERLY WINDS ALOFT...ASSOCIATED WITH THE SUBTROPICAL
JET STREAM. IN THE LATER PERIODS THE FORECAST ANTICIPATES THAT A
MUCH WEAKER AND SHALLOWER HILDA WILL BEGIN TO MOVE TOWARD THE
WEST-NORTHWEST WITH A GRADUAL INCREASE IN FORWARD SPEED AS IT IS
STEERED BY THE LOW-LEVEL TRADE WIND FLOW.

THE 0600Z RUN OF THE GFS OFFERED A DRAMATICALLY DIFFERENT TRACK AND
INTENSITY SOLUTION THAN PREVIOUS RUNS...WITH A MUCH WEAKER HILDA
MOVING NEARLY DUE WEST OVER THE NEXT 3 DAYS AND PASSING WELL SOUTH
OF THE BIG ISLAND BY TUESDAY NIGHT OR WEDNESDAY. THIS CONTRADICTS
ECMWF GUIDANCE...WHICH SHOWS A FAIRLY WEAK HILDA MOVING NORTHWEST
OVER WINDWARD WATERS OF THE HAWAIIAN ISLANDS BEFORE EVENTUALLY
MOVING WEST NEAR KAUAI TOWARDS THE END OF THE WEEK. THIS RECENT
DIVERGENCE IN SOLUTIONS FROM SOME OF THE MORE RELIABLE TRACK MODELS
IS LIKELY DUE TO DIFFERENCES IN THE DEPTH OF THE FORECAST
CIRCULATION...AND LEADS TO DECREASED CONFIDENCE IN THE OFFICIAL
TRACK FORECAST. WITH THE SOMEWHAT DRAMATIC CHANGES NOTED IN RECENT
MODEL RUNS...THE UPDATED TRACK FORECAST OFFERS LITTLE CHANGE FROM
THE PREVIOUS.

THE INTENSITY FORECAST ALSO CONTAINS LITTLE SIGNIFICANT CHANGE FROM
THE PREVIOUS...WITH STRONG VERTICAL WIND SHEAR LEADING TO A
SIGNIFICANT WEAKENING OF THE CYCLONE THROUGH THE FORECAST PERIOD.
THE WEAKENING TREND IN THE OFFICIAL FORECAST IS NOT AS RAPID AS
INDICATED BY SHIPS...BUT STILL ANTICIPATES THAT HILDA WILL WEAKEN TO
A TROPICAL STORM ON TUESDAY...SIMILAR TO THE IVCN CONSENSUS.

ALTHOUGH THE CURRENT FORECAST BRINGS HILDA NEAR THE BIG ISLAND AS A
TROPICAL DEPRESSION LATER THIS WEEK...UNCERTAINTY REMAINS AS TO THE
EVENTUAL IMPACTS THAT MAY BE FELT IN THE HAWAIIAN ISLANDS. INTERESTS
IN HAWAII SHOULD CLOSELY MONITOR THE PROGRESS OF HILDA...AND A
TROPICAL STORM WATCH MAY BE REQUIRED FOR THE BIG ISLAND LATER TODAY
OR TONIGHT. IT IS IMPORTANT NOT TO FOCUS TOO CLOSELY ON THE EXACT
TRACK AND INTENSITY FORECASTS BECAUSE AVERAGE INTENSITY ERRORS ARE
NEAR 35 MPH ON DAY 5...AND AVERAGE TRACK ERRORS ARE NEAR 175 MILES.
IN ADDITION...THE HAZARDS OF A TROPICAL CYCLONE CAN EXTEND OVER A
BROAD AREA AWAY FROM THE CENTER.


FORECAST POSITIONS AND MAX WINDS

INIT 10/1500Z 16.2N 149.8W 80 KT 90 MPH
12H 11/0000Z 16.8N 150.8W 70 KT 80 MPH
24H 11/1200Z 17.3N 151.6W 60 KT 70 MPH
36H 12/0000Z 17.8N 152.3W 45 KT 50 MPH
48H 12/1200Z 18.4N 153.2W 40 KT 45 MPH
72H 13/1200Z 19.0N 154.6W 30 KT 35 MPH
96H 14/1200Z 19.5N 156.0W 30 KT 35 MPH
120H 15/1200Z 20.0N 158.5W 25 KT 30 MPH...POST-TROP/REMNT LOW

$$

FORECASTER BIRCHARD

[NDG]

This might be a silly question but why is there always a wall of strong wind shear over or around Hawaii?

Seems to be because of a semi permanent TUTT like feature near Hawaii just like it happens this time of the year most times over the eastern Caribbean.
My non-scientific amateur explanation is this: maybe because of UL dynamics, lots of rising air over the western tropical Pacific and lots of rising air over the eastern tropical pacific creates a TUTT over the central pacific.

[Kingarabian]

This might be a silly question but why is there always a wall of strong wind shear over or around Hawaii?

Seems to be because of a semi permanent TUTT like feature near Hawaii just like it happens this time of the year most times over the eastern Caribbean.
My non-scientific amateur explanation is this: maybe because of UL dynamics, lots of rising air over the western tropical Pacific and lots of rising air over the eastern tropical pacific creates a TUTT over the central pacific.

Spot on!

[Kingarabian]

Shear is kicking in. Eye has reappeared.

[Kingarabian]

18z GFS still misses Hawaii to the south.

I don't understand why the CPHC is putting so much weight on it considering it continues to under-initialize Hilda. Has it at 994mb.

[cycloneye]

HURRICANE HILDA DISCUSSION NUMBER 20
NWS CENTRAL PACIFIC HURRICANE CENTER HONOLULU HI EP102015
1100 AM HST MON AUG 10 2015

THE U.S. 53RD WEATHER RECONNAISSANCE AIRCRAFT WHICH SAMPLED THE
INNER CORE OF HILDA EARLIER THIS MORNING...INDICATED MAX SUSTAINED
WINDS FROM SFMR DATA OF 85 KNOTS. MEANWHILE...SURFACE WINDS FROM
THE MBL WIND DATA INDICATED 77 KNOTS...FROM THE WL150 DATA 74
KNOTS...AND FROM A REDUCTION OF THE MAX FLIGHT LEVEL WINDS RESULTED
IN SURFACE WINDS OF 82 KNOTS. BASED ON THE POTENTIAL OF SOME RAIN
CONTAMINATION IN THE SFMR WINDS...WE USED A BLENDED APPROACH FOR
THE INITIAL INTENSITY ESTIMATE. AS A RESULT...THE INITIAL INTENSITY
WAS KEPT AT 80 KNOTS FOR THIS ADVISORY. THE INITIAL MOTION IS
BASED ON THE AIRCRAFT FIXES AND SATELLITE EXTRAPOLATION...AND WILL
BE SET AT 300 DEGREES AT 7 KNOTS. THE SATELLITE PRESENTATION OF
HILDA CONTINUES TO SLOWLY DEGRADE AS THE SYSTEM ENCOUNTERS
INCREASING WESTERLY VERTICAL WIND SHEAR. THIS IS CONFIRMED BY THE
LATEST UW-CIMSS VERTICAL WIND SHEAR ANALYSIS WHICH SHOWS 36 KNOTS
FROM 260 DEGREES. MEANWHILE...THE LATEST FIXES FROM PHFO...SAB AND
JTWC INDICATED T NUMBERS OF 4.5 TO 5.0 OR 77 TO 90 KNOTS.

HILDA REMAINS WITHIN A WEAKNESS IN THE MID TO UPPER LEVEL RIDGE
EXTENDING FROM A LOW ALOFT NEAR 27N156W...SOUTHEASTWARD TO THE
TROPICAL CYCLONE. WITH THE LOW ALOFT WELL TO THE NORTHWEST OF THE
SYSTEM EXPECTED TO RETROGRADE OFF TO THE NORTHWEST OVER THE NEXT
COUPLE DAYS...EXPECT THAT HILDA WILL CONTINUE TO TRACK SLOWLY OFF
TO THE WEST-NORTHWEST...WHICH IS SUPPORTED BY THE LATEST MODEL
CONSENSUS. THE MODEL GUIDANCE HAS INDICATED A SLOWING IN THE
FORWARD SPEED OF THE SYSTEM AS IT ENCOUNTERS INCREASING WESTERLY
WIND SHEAR OVER THE NEXT SEVERAL DAYS...AND THIS SEEMS REASONABLE AS
THE SYSTEM BECOMES INCREASINGLY TILTED AND LOSES DEEP CONVECTION. AS
A RESULT...THE FORECAST TRACK WILL REMAIN VERY CLOSE TO THE
PREVIOUS ADVISORY...WITH A SLOWING IN THE FORWARD SPEED OF THE
SYSTEM THROUGH 72 HOURS. THIS IS CLOSELY IN LINE WITH WITH THE
LATEST TVCN. BEYOND 72 HOURS...THE SHEAR IS EXPECTED TO HAVE TAKEN A
LARGE TOLL ON HILDA...WHICH SHOULD ALLOW IT TO GET INCREASINGLY
CAUGHT UP WITHIN THE TRADE WIND FLOW. AS A RESULT...WILL SHOW A
SLIGHT INCREASE IN FORWARD SPEED AND A SLIGHT BEND TOWARD THE LEFT
OR SOUTH OF THE PREVIOUS FORECAST TRACK FOR THE 96 AND 120 HOUR
POINTS.

THE INTENSITY FORECAST FOR HILDA WILL BE HIGHLY DEPENDENT ON THE
INCREASING WESTERLY WIND SHEAR OVER THE SYSTEM. THE COMBINATION OF
SHEAR AND VERY DRY MID LEVEL AIR TO THE WEST OF THE SYSTEM WHICH IS
EVIDENT IN WATER VAPOR IMAGERY...SHOULD ALLOW FOR SLOW AND STEADY
WEAKENING THROUGH THE FORECAST PERIOD. THE OFFICIAL INTENSITY
FORECAST IS VERY CLOSE TO ICON...AND WILL SHOW HILDA WEAKENING TO
TROPICAL STORM STRENGTH ON TUESDAY AND BECOMING A TROPICAL
DEPRESSION THURSDAY NIGHT OR FRIDAY.




FORECAST POSITIONS AND MAX WINDS

INIT 10/2100Z 16.3N 150.2W 80 KT 90 MPH
12H 11/0600Z 16.7N 150.8W 70 KT 80 MPH
24H 11/1800Z 17.2N 151.5W 60 KT 70 MPH
36H 12/0600Z 17.7N 152.2W 50 KT 60 MPH
48H 12/1800Z 18.1N 153.0W 45 KT 50 MPH
72H 13/1800Z 18.8N 154.8W 35 KT 40 MPH
96H 14/1800Z 19.4N 157.2W 30 KT 35 MPH
120H 15/1800Z 19.9N 160.1W 25 KT 30 MPH...POST-TROP/REMNT LOW

$$
FORECASTER JELSEMA/DONALDSON

[Yellow Evan]

This might be a silly question but why is there always a wall of strong wind shear over or around Hawaii?

Seems to be because of a semi permanent TUTT like feature near Hawaii just like it happens this time of the year most times over the eastern Caribbean.
My non-scientific amateur explanation is this: maybe because of UL dynamics, lots of rising air over the western tropical Pacific and lots of rising air over the eastern tropical pacific creates a TUTT over the central pacific.

More so this year than other years since the TUTT is stronger in super El Nino years.

[Kingarabian]

Holding strong.

[Kingarabian]

TXPN24 KNES 110009
TCSCNP

A. 10E (HILDA)

B. 10/2330Z

C. 16.6N

D. 150.6W

E. THREE/GOES-W

F. T4.5/4.5/S0.0/24HRS

G. IR/EIR/VIS

H. REMARKS...OVERALL CLOUD PATTERN IS ELONGATING N-S DUE TO SHEAR BUT
DT=4.5 BASED ON CENTER EMBEDDED IN LIGHT GRAY CONVECTION. MET AND PAT
ALSO 4.5. FT IS BASED ON DT.

I. ADDL POSITIONS

NIL


...SWANSON

[Kingarabian]

It's moving to the left of track and more north. Think they need to adjust the track.

[Yellow Evan]

It's holding in there like Guillermo was (30 knots of GHS shear seems to be somewhat less than 30 knots of non-GHS), but it slowly weakening.

Given that it is holding up, I'd expect some northerly shifts soon.

[Yellow Evan]

It's moving to the left of track and more north. Think they need to adjust the track.

CPHC has been moving this way too slowly the entire time.

[Kingarabian]

It's holding in there like Guillermo was (30 knots of GHS shear seems to be somewhat less than 30 knots of non-GHS), but it slowly weakening.

Given that it is holding up, I'd expect some northerly shifts soon.

I agree.

And I know two storms are almost never the same but Guillermo was weaker on its initial approach and held through as a tropical storm as it rounded up the islands.