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Hurricane TOMAS


ZCZC MIATCDAT1 ALL
TTAA00 KNHC DDHHMM
HURRICANE TOMAS DISCUSSION NUMBER   9
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL212010
500 AM AST SUN OCT 31 2010

DATA FROM THE AIR FORCE RESERVE HURRICANE HUNTER AIRCRAFT...ALONG
WITH SATELLITE AND RADAR IMAGERY...INDICATE THAT TOMAS HAS BECOME
BETTER ORGANIZED IN THE PAST FEW HOURS. THE INITIAL INTENSITY OF 85
KT IS BASED ON A 700-MB FLIGHT LEVEL WIND MAXIMUM OF 97 KT AND A
MAXIMUM SFMR READING OF 85 KT. HOWEVER...DROPSONDE DATA FROM THE
AIRCRAFT AND A 0350 UTC TRMM PASS INDICATE THAT THE VORTEX IS
TILTED NORTHEASTWARD WITH HEIGHT. THIS SUGGESTS THAT SOUTHWESTERLY
SHEAR IS IMPACTING THE CYCLONE AS SEEN IN THE SHIPS MODEL ANALYSIS
WHICH IS BASED ON ATMOSPHERIC FIELDS FROM THE GFS MODEL. IN THE
SHORT TERM...THE SHIPS...LGEM...AND GFDL ALL SHOW SOME ADDITIONAL
INTENSIFICATION...AND SO DOES THE OFFICIAL FORECAST. FROM 24 TO 72
HOURS...THE SHIPS MODEL SHOWS THE SHEAR INCREASING...AND ALL OF THE
INTENSITY GUIDANCE WEAKENS TOMAS. ADDITIONALLY...THE GFS AND ECMWF
SHOW THE MID-LEVEL VORTEX ASSOCIATED WITH TOMAS WEAKENING DURING
THIS PERIOD. GIVEN THIS...THE OFFICIAL FORECAST WILL SHOW A SLIGHT
DIP IN THE INTENSITY AT 48 AND 72 HOURS...BUT REMAINS WELL ABOVE
ALL OF THE GUIDANCE. AROUND 96 HOURS...THE SHEAR MAY DECREASE AND
ALLOW FOR SOME STRENGTHENING...AS INDICATED BY THE LGEM. 

BASED ON RECENT FIXES TOMAS IS A BIT NORTH OF THE PREVIOUS TRACK
FORECAST AND THE LONG-TERM INITIAL MOTION ESTIMATE IS 290/7. TOMAS
IS CURRENTLY LOCATED SOUTH OF A MID-LEVEL TROUGH SITUATED OVER THE
SOUTHWEST ATLANTIC. AS THIS TROUGH MOVES EASTWARD...A MID-LEVEL
RIDGE BUILDS NORTH OF TOMAS AND SHOULD RESULT IN A TURN TOWARD THE
WEST IN 2 OR 3 DAYS. LATE IN THE PERIOD...THE RIDGE BREAKS DOWN AS
A LARGE DEEP-LAYER TROUGH MOVES INTO EASTERN NORTH AMERICA...
RESULTING IN A SLOWER FORWARD SPEED OF THE CYCLONE AND SOME GAIN IN
LATITUDE. HOWEVER...THE MODEL SPREAD IS QUITE LARGE AT DAYS 4 AND 5
DUE TO DIFFERENCES IN THE TIMING AND SHARPNESS OF THE NORTHWARD
TURN AS TOMAS INTERACTS WITH THE TROUGH. THE NEW NHC TRACK IS A
LITTLE NORTH OF THE PREVIOUS ONE DUE TO THE INITIAL POSITION...BUT
IS ON THE SOUTH SIDE OF THE GUIDANCE SUITE IN DEFERENCE TO THE
GFS...ECMWF...UKMET AND GFDL MODELS...WHICH ARE ALL EVEN FARTHER
SOUTH. AT DAY 5...A SLOW NORTH-NORTHWESTWARD MOTION IS SHOWN...BUT
CONFIDENCE IN THE DETAILS OF THE TRACK FORECAST ARE LOWER THAN
USUAL AT THE END OF THE PERIOD. 

FORECAST POSITIONS AND MAX WINDS
 
INITIAL      31/0900Z 14.0N  62.9W    85 KT
 12HR VT     31/1800Z 14.4N  64.3W    95 KT
 24HR VT     01/0600Z 14.8N  66.4W    95 KT
 36HR VT     01/1800Z 15.1N  68.4W    95 KT
 48HR VT     02/0600Z 15.1N  70.0W    90 KT
 72HR VT     03/0600Z 15.0N  72.0W    90 KT
 96HR VT     04/0600Z 15.5N  73.5W   100 KT
120HR VT     05/0600Z 16.5N  74.0W   100 KT
 
$$
FORECASTER BRENNAN
 
NNNN


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Page last modified: Friday, 15-Apr-2011 12:09:25 UTC