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| #386630 (Received by flhurricane at: 4:46 AM 31.Oct.2010) TCDAT1 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 |
