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| #6093 (Received by flhurricane at: 4:50 PM 25.Aug.2004) TCDAT1 TROPICAL STORM FRANCES DISCUSSION NUMBER 4 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 5 PM EDT WED AUG 25 2004 AFTER LOOKING RAGGED THIS MORNING...THE CONVECTION ASSOCIATED WITH TROPICAL DEPRESSION SIX HAS BECOME BETTER ORGANIZED THIS AFTERNOON WITH A SMALL CENTRAL DENSE OVERCAST AND A BAND WRAPPED AROUND THE WESTERN SEMICIRCLE. SATELLITE INTENSITY ESTIMATES ARE 35 KT FROM TAFB AND SAB...SO THE DEPRESSION IS UPGRADED TO TROPICAL STORM FRANCES WITH 35 KT WINDS. THE INITIAL MOTION IS 275/15. THE CYCLONE REMAINS SOUTH OF A SUBTROPICAL RIDGE. LARGE-SCALE MODELS INDICATE THAT A MID/ UPPER-LEVEL LEVEL LOW CURRENTLY SEEN IN WATER VAPOR IMAGERY SOUTH OF NEWFOUNDLAND WILL DIVE SOUTHEASTWARD AND WEAKEN THE RIDGE FROM 48-96 HR...AND THEN LIFT OUT TO THE NORTHEAST. IF THIS VERIFIES... IT WOULD ALLOW FRANCES TO TURN NORTHWESTWARD AFTER 24 HR...AND THEN POSSIBLY TURNING MORE WESTWARD BY 120 HR AS THE RIDGE REBUILDS TO THE NORTH. THE DYNAMICAL MODELS GENERALLY AGREE WITH THIS SCENARIO. HOWEVER...THE GFS TRACK REMAINS TO THE SOUTH AND WEST OF THE GFDL...UKMET...AND NOGAPS. THE OFFICIAL FORECAST TRACK FOLLOWS THIS SCENARIO AND IS SHIFTED JUST A LITTLE WEST OF THE PREVIOUS PACKAGE...IN BEST AGREEMENT WITH THE GFDL AND WEST OF ALL THE DYNAMICAL MODELS EXCEPT THE GFS. CONDITIONS GENERALLY APPEAR FAVORABLE FOR STRENGTHENING FOR THE FIRST 72-96 HR...WITH THE ONLY SEEMING NEGATIVE FACTOR BEING THE DRY AIR SURROUNDING FRANCES IN WATER VAPOR IMAGERY. THE INTENSITY FORECAST WILL CALL FOR SLOW STRENGTHENING FOR THE FIRST 36 HR OR SO IN AGREEMENT WITH THE CURRENT ORGANIZATION AND TRENDS...THEN CALL FOR FASTER DEVELOPMENT AS THE SYSTEM NEARS HURRICANE STRENGTH. AFTER 72-96 HR...IF THE CYCLONE TRACKS AS FAR NORTH AS FORECAST...IT MAY ENCOUNTER WESTERLY SHEAR TO THE NORTH OF THE UPPER-LEVEL RIDGE FORECAST TO LIE EAST- WEST ALONG 18-19N. THAT WOULD LIMIT STRENGTHENING AS INDICATED IN THE FORECAST. A CONTINUING ALTERNATE SCENARIO WOULD BE IF THE CYCLONE STAYS SOUTH OF THE RIDGE AXIS...WHICH WOULD ALLOW GREATER STRENGTHENING THAN CURRENTLY FORECAST. FORECASTER BEVEN FORECAST POSITIONS AND MAX WINDS INITIAL 25/2100Z 11.6N 40.5W 35 KT 12HR VT 26/0600Z 12.0N 42.7W 40 KT 24HR VT 26/1800Z 13.0N 45.0W 45 KT 36HR VT 27/0600Z 13.9N 46.6W 50 KT 48HR VT 27/1800Z 14.9N 48.1W 60 KT 72HR VT 28/1800Z 17.0N 50.5W 70 KT 96HR VT 29/1800Z 18.5N 52.5W 80 KT 120HR VT 30/1800Z 20.5N 55.5W 80 KT |
