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Hurricane TOMAS


ZCZC MIATCDAT1 ALL
TTAA00 KNHC DDHHMM
HURRICANE TOMAS DISCUSSION NUMBER   6
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL212010
500 PM AST SAT OCT 30 2010
 
AN AIR FORCE RESERVE HURRICANE HUNTER AIRCRAFT INVESTIGATING TOMAS
THIS AFTERNOON FOUND MAXIMUM 700 MB FLIGHT-LEVEL WINDS OF 67 KT IN
THE NORTH QUADRANT...WHICH EQUATES TO ABOUT 60 KT SURFACE WINDS.
SATELLITE INTENSITY ESTIMATES ARE A CONSENSUS T4.0/65 KT FROM TAFB
AND SAB. THE STRUCTURE OF TOMAS HAS IMPROVED CONSIDERABLY IN RADAR
IMAGERY FROM MARTINIQUE...AND THE CYCLONE NOW POSSESSES A CLOSED 25
N MI DIAMETER EYE. THE INTENSITY IS BEING HELD AT 65 KT FOR THIS
ADVISORY...WHICH COULD BE A LITTLE LOW BASED ON SOME OF THE DAMAGE
REPORTS THAT HAVE BEEN RECEIVED FROM HAM RADIO OPERATORS ON ST.
LUCIA AND ST. VINCENT.

THE INITIAL MOTION ESTIMATE IS 290/09. TOMAS REMAINS ON TRACK...
AND THERE IS NO SIGNIFICANT CHANGE TO THE PREVIOUS FORECAST TRACK OR
REASONING. THE LOW- TO MID-LEVEL RIDGE TO THE NORTH OF TOMAS IS
EXPECTED TO CONTINUE TO BUILD WESTWARD ACROSS THE GREATER ANTILLES
FOR THE NEXT 96 HOURS...WHICH SHOULD KEEP TOMAS ON A WEST-NORTHWEST
TO WESTWARD TRACK. HOWEVER...A BROAD LONGWAVE TROUGH CURRENTLY
ALONG THE U.S. WEST COAST IS EXPECTED TO MOVE EASTWARD AND THEN
SOUTHEASTWARD INTO THE SOUTHEASTERN UNITED STATES...AND PINCH OFF A
CLOSED LOW OVER THE GULF OF MEXICO AND SOUTHEASTERN MEXICO BY 120
HOURS. THE STRONG SOUTHWESTERLY FLOW ON THE EAST SIDE OF THE
AFOREMENTIONED TROUGH AND LOW IS EXPECTED TO RESULT IN A
SIGNIFICANT EROSION OF THE WESTERN PORTION OF THE GREATER ANTILLES
RIDGE AND CAUSE THE STEERING CURRENTS ACROSS THE WESTERN AND
CENTRAL CARIBBEAN SEA TO WEAKEN...ALLOWING TOMAS TO SLOW DOWN
CONSIDERABLY AND BEGIN TO MOVE POLEWARD. MOST OF THE MODEL GUIDANCE
IS IN GOOD AGREEMENT ON THIS GENERAL TRACK SCENARIO EXCEPT FOR
SPEED DIFFERENCES. THE OFFICIAL FORECAST TRACK IS JUST AN UPDATE OF
THE PREVIOUS ADVISORY TRACK...AND REMAINS ALONG THE SOUTHERN EDGE
OF THE NHC GUIDANCE ENVELOPE...BUT NOT AS FAR SOUTH AS THE GFS AND
ECMWF MODELS.
 
WITH A CLOSED EYE AND A FAVORABLE UPPER-LEVEL ENVIRONMENT...TOMAS IS
FORECAST TO STRENGTHEN FOR THE NEXT 24 HOURS OR SO BEFORE WEAK
WESTERLY 400-300 MB WINDS UNDERCUT THE IMPRESSIVE OUTFLOW LAYER AND
ENTRAINMENT OF DRY MID-LEVEL AIR FROM THE WEST COMBINE TO INTERRUPT
THE STRENGTHENING PROCESS. HOWEVER...BY 48-72 HOURS...ENVIRONMENTAL
CONDITIONS ARE FORECAST TO IMPROVE...WHICH SHOULD ALLOW TOMAS TO
RESUME STEADY INTENSIFICATION. THE GFS-BASED SHIPS AND LGEM MODELS
ARE FORECASTING STEADY WEAKENING AFTER 48 HOURS...BUT THAT IS
BELIEVED TO BE DUE TO ERRONEOUS MODEL-INDUCED SOUTHWESTERLY
VERTICAL SHEAR AFFECTING TOMAS AS A RESULT OF THE OFFICIAL FORECAST
TRACK BEING ABOUT 120 N MI NORTH OF THE LARGE SCALE UPPER-LEVEL
ANTICYCLONE DEPICTED IN THE GFS MODEL. THE INTENSITY FORECAST
REMAINS ABOVE THE SHIPS/LGEM MODELS...AND IS SIMILAR TO THE
PREVIOUS FORECAST AND LAST TWO GFDL MODEL RUNS.
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      30/2100Z 13.5N  61.4W    65 KT
 12HR VT     31/0600Z 14.0N  63.4W    75 KT
 24HR VT     31/1800Z 14.5N  65.7W    80 KT
 36HR VT     01/0600Z 14.9N  67.9W    80 KT
 48HR VT     01/1800Z 15.2N  69.7W    85 KT
 72HR VT     02/1800Z 15.7N  72.4W    90 KT
 96HR VT     03/1800Z 16.0N  74.0W    95 KT
120HR VT     04/1800Z 16.5N  74.5W   100 KT
 
$$
FORECASTER STEWART
 
NNNN


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