HURRICANE TOMAS DISCUSSION NUMBER 32

By: National Hurricane Center
By: National Hurricane Center

WTNT41 KNHC 060241
TCDAT1
HURRICANE TOMAS DISCUSSION NUMBER 32
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL212010
1100 PM EDT FRI NOV 05 2010

BEFORE DEPARTING EARLIER THIS EVENING...THE AIR FORCE RESERVE
HURRICANE HUNTER AIRCRAFT FOUND A MAXIMUM 850-MB FLIGHT LEVEL WIND
OF 57 KT AND A RISING CENTRAL PRESSURE. THE SATELLITE APPEARANCE OF
THE CYCLONE HAD ALSO BECOME A BIT DISHEVELED EARLIER THIS EVENING
...HOWEVER COLD CLOUD TOPS HAVE AGAIN INCREASED NEAR THE ESTIMATED
CENTER LOCATION. THE INITIAL INTENSITY IS HELD AT 65 KT...AND THE
NEXT AIRCRAFT MISSION OVERNIGHT WILL HELP DETERMINE IF TOMAS HAS
WEAKENED BELOW HURRICANE INTENSITY. THE 20 KT OF SOUTHERLY SHEAR
OVER TOMAS ASSOCIATED WITH THE LARGE DEEP-LAYER TROUGH MOVING
ACROSS EASTERN NORTH AMERICA COULD BE PREVENTING THE CYCLONE FROM
STRENGTHENING FURTHER. CONSISTENT WITH THIS THINKING...AIRCRAFT
DATA AND RECENT MICROWAVE IMAGERY INDICATE THAT THE VORTEX IS NOW
TILTED NORTHEASTWARD WITH HEIGHT. GIVEN THE SHEAR AND THE RAPID
DETERIORATION OF THE MID-LEVEL ATMOSPHERIC THERMODYNAMICS AS
INDICATED BY THE SHIPS MODEL IN THE NEXT 12 TO 24 HOURS...TOMAS MAY
HAVE PEAKED IN INTENSITY. BEYOND 24 HOURS...THE SHEAR INCREASES
FURTHER...WHICH SHOULD RESULT IN WEAKENING. THE OFFICIAL INTENSITY
FORECAST HAS BEEN ADJUSTED DOWNWARD...AND SHOWS LITTLE CHANGE
THROUGH 12 HOURS FOLLOWED BY STEADY WEAKENING TO REMNANT LOW STATUS
IN 96 HOURS. THIS FORECAST IS CLOSE TO THE LGEM MODEL...WHICH IS
DESIGNED TO HANDLE CHANGING ENVIRONMENTAL CONDITIONS DURING THE
FORECAST PERIOD.

THE LAST FEW AIRCRAFT FIXES INDICATE THAT TOMAS IS MOVING MORE TO
THE RIGHT...OR EASTWARD...THAN THE PREVIOUS FORECAST TRACK...AND
THE INITIAL MOTION ESTIMATE IS 045/11 KT. THE GLOBAL MODELS ARE IN
RELATIVELY GOOD AGREEMENT ON THE EVOLUTION OF THE LARGE-SCALE
PATTERN...WHICH IS DOMINATED BY A DEEP-LAYER TROUGH MOVING INTO THE
WESTERN ATLANTIC THAT WILL SLOW DOWN AS IT CUTS OFF OFFSHORE OF THE
NORTHEASTERN U.S. IN 2 OR 3 DAYS. SIGNIFICANT DIFFERENCES REMAIN IN
THE TRACK GUIDANCE AS TO WHETHER TOMAS WILL BE PULLED NORTHWARD
INTO THE SURFACE FRONTAL ZONE ASSOCIATED WITH THE TROUGH OR BE
SHEARED APART AND MOVE SLOWLY EASTWARD. THE GFS...ECMWF...AND UKMET
FAVOR THE LATTER SOLUTION AND LIE ON THE SOUTHERN SIDE OF THE
GUIDANCE ENVELOPE. THE GFDL...HWRF AND NOGAPS ARE FARTHER NORTH
WITH A DEEPER CYCLONE. GIVEN THE EXTREME SHEAR VALUES LATE IN THE
PERIOD AND AN ENVIRONMENT THAT APPEARS UNFAVORABLE FOR DEEP
CONVECTION...IT SEEMS UNLIKELY THAT TOMAS WILL REMAIN DEEP ENOUGH
TO BE PULLED TOO FAR NORTHWARD. THE OFFICIAL FORECAST FAVORS THE
SOUTHERN SOLUTION AND IS BASED ON A BLEND OF THE PREVIOUS FORECAST
AND THE TRACKS OF THE UKMET...GFS...AND ECMWF MODELS THROUGH 48
HOURS. AT DAYS 3 AND 4...THE NEW NHC FORECAST IS AN UPDATE OF THE
PREVIOUS ONE ADJUSTED FOR THE INITIAL POSITION AND MOTION.

EVEN THOUGH THE CENTER OF TOMAS HAS PASSED NORTH OF HISPANIOLA...
SOUTHERLY FLOW BEHIND TOMAS WILL RESULT IN THE CONTINUATION OF A
SIGNIFICANT HEAVY RAINFALL THREAT FOR THE NEXT DAY OR TWO...WHICH
COULD PRODUCE FLASH FLOODING AND LIFE-THREATENING MUD SLIDES OVER
PORTIONS OF HAITI AND THE DOMINICAN REPUBLIC.

FORECAST POSITIONS AND MAX WINDS

INITIAL 06/0300Z 20.8N 72.8W 65 KT
12HR VT 06/1200Z 22.4N 71.7W 65 KT
24HR VT 07/0000Z 23.9N 70.9W 60 KT
36HR VT 07/1200Z 24.7N 70.1W 55 KT
48HR VT 08/0000Z 25.0N 68.8W 45 KT
72HR VT 09/0000Z 26.0N 66.0W 30 KT
96HR VT 10/0000Z 26.0N 63.0W 20 KT...POST-TROP/REMNT LOW
120HR VT 11/0000Z...DISSIPATED

$$
FORECASTER BRENNAN/ROBERTS


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