ZCZC MIATCDAT1 ALL TTAA00 KNHC DDHHMM HURRICANE FRANCES DISCUSSION NUMBER 41 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 11 PM EDT FRI SEP 03 2004 RADAR...SATELLITE...RECON DATA...AND NUMEROUS SURFACE REPORTS FROM HAM RADIO OPERATORS...SURFACE STATIONS...AND SHIPS IN AND AROUND THE CENTRAL AND NORTHWESTERN BAHAMAS...AND THE FLORIDA EAST COAST INDICATE THAT FRANCES HAS WEAKENED SINCE THE 18Z ADVISORY. HOWEVER ...THE SURFACE PRESSURE IN THE EYE HAS NOT CHANGED FROM 959-960 MB SINCE ABOUT 22Z. BRIEF BURSTS OF DEEP CONVECTION HAVE BEEN DEVELOPING IN THE NORTHERN SEMICIRCLE WHICH HAVE BEEN HELPING TO MAINTAIN A 90-KT INTENSITY. THE INITIAL MOTION HAS SLOWED TO 295/05. DROPSONDE DATA AND 18Z UPPER-AIR DATA INDICATE THE WRAPAROUND MID-LEVEL RIDGE TO THE NORTH OF FRANCES HAS NOT MOVED...WITH A HIGH CENTER LOCATED OVER SOUTHEAST GEORGIA AND RIDGES EXTENDING EASTWARD AND SOUTHWESTWARD FROM THE HIGH FOR SEVERAL HUNDRED MILES. THIS HAS TRAPPED FRANCES IN A WEAK STEERING REGIME...WHICH IS EXPECTED TO LAST FOR AT LEAST THE NEXT 36 HOURS. AFTER THAT...THE RIDGE OVER THE EASTERN GULF OF MEXICO IS FORECAST BY ALL OF THE MODELS TO ERODE SLOWLY EASTWARD AND ALLOW FRANCES TO TURN NORTHWESTWARD AND THEN NORTHWARD BY 72 HOURS. IT IS INTERESTING TO POINT OUT THAT THE GFDL AND GFS MODELS THAT PREVIOUSLY FOR SEVERAL DAYS HAD BEEN THE RIGHTMOST OF THE NHC MODEL SUITE ARE NOW THE LEFTMOST MODELS...AND TAKE FRANCES ACROSS THE NORTHERN PORTION OF LAKE OKEECHOBEE IN ABOUT 36 HOURS. THE OFFICIAL TRACK IS SLIGHTLY LEFT OF THE PREVIOUS TRACK AND TO THE LEFT OF THE GUNA CONSENSUS MODEL. SOME WESTERLY WINDS BETWEEN 300-250 MB HAVE BEEN UNDERCUTTING THE IMPRESSIVE UPPER-LEVEL OUTFLOW LAYER. THIS UNFAVORABLE SHEAR PATTERN...COMBINED WITH MID-LEVEL DRY AIR ENTRAINMENT...HAS LIKELY LED TO THE WEAKENING OVER THE PAST 24 HOURS. THE GFS-ETA-GFDL MODELS FORECAST THE SHEAR PATTERN TO WEAKEN OR DISAPPEAR IN 18-24 HOURS...AT ABOUT THE TIME FRANCES IS SLOWLY CROSSING THE WARMER GULFSTREAM. HOWEVER...GIVEN THE ALREADY EXPANDED AND LARGE INNER CORE WIND FIELD...ONLY SLIGHT INTENSIFICATION IS EXPECTED. THIS SCENARIO IS SIMILAR TO THE GFDL INTENSITY FORECAST. BECAUSE FRANCES IS A SLOW MOVING HURRICANE...IT COULD BRING TORRENTIAL RAINS TO PORTIONS OF FLORIDA SATURDAY NIGHT AND SUNDAY. FORECASTER STEWART FORECAST POSITIONS AND MAX WINDS INITIAL 04/0300Z 26.1N 77.8W 90 KT 12HR VT 04/1200Z 26.5N 78.6W 90 KT 24HR VT 05/0000Z 27.0N 79.8W 95 KT 36HR VT 05/1200Z 27.6N 81.2W 55 KT...INLAND 48HR VT 06/0000Z 28.7N 83.1W 35 KT...OVER GULF OF MEXICO 72HR VT 07/0000Z 31.9N 86.2W 30 KT...INLAND 96HR VT 08/0000Z 35.0N 87.0W 25 KT...INLAND 120HR VT 09/0000Z 40.0N 84.5W 20 KT...INLAND $$ NNNN
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Page last modified: Saturday, 04-Sep-2004 03:02:46 UTC