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| #6148 (Received by flhurricane at: 10:59 AM 26.Aug.2004) TCDAT1 TROPICAL STORM FRANCES DISCUSSION NUMBER 7 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 11 AM EDT THU AUG 26 2004 FRANCES HAS BECOME MUCH BETTER ORGANIZED DURING THE PAST 12 HOURS... AS NOTED BY THE TIGHT COILING OF BOTH THE INNER AND OUTER CONVECTIVE BANDS...AND AN OCCASIONAL HINT OF A BANDING EYE FEATURE. A DVORAK SATELLITE INTENSITY ESTIMATE OF T3.5 WAS OBTAINED FROM BOTH TAFB AND SAB. HOWEVER...BANDING FEATURES AND INNER-CORE CONVECTION HAVE IMPROVED SINCE THE 12Z FIXES...SO I HAVE CONTINUED THE TREND FROM THE PREVIOUS ADVISORY OF GOING SLIGHTLY HIGHER THAN THE SATELLITE ESTIMATES ARE INDICATING. UPPER-LEVEL OUTFLOW IS GOOD IN ALL QUADRANTS AND IS BECOMING MORE CIRCULAR. THE INITIAL MOTION REMAINS 290/15. FRANCES HAS BASICALLY REMAINED ON TRACK THE PAST 24 HOURS. HOWEVER...THE NHC MODEL GUIDANCE IS NOT IN GOOD AGREEMENT AFTER 36 HOURS. THE NOGAPS...UKMET...AND ECMWF TAKE FRANCES MORE NORTHWESTWARD THOUGHOUT THE FORECAST PERIOD...WHEREAS THE GFDL...GFS...AND THE CANADIAN MODELS TAKE THE CYCLONE MORE WEST-NORTHWESTWARD AND EVEN WESTWARD. THE MAIN DIFFERENCES LIE IN HOW MUCH EROSION OF THE SUBTROPICAL RIDGE OCCURS NORTH OF FRANCES IN 36-72 HOURS AS A LARGE EXTRATROPICAL LOW OFF THE CANADIAN MARITIMES DIGS SOUTHWARD. THE UKMET AND NOGAPS MODEL SHOW MORE EROSION OF THE RIDGE...WHILE THE GFS...GFDL...AND CANADIAN MODELS LIFT OUT THE UPPER-LOW MORE QUICKLY...WHICH ALLOWS THE RIDGE TO BUILD BACK WESTWARD TO THE NORTH OF THE CYCLONE AFTER 72 HOURS. THE PAST 24 HOUR TREND IN WATER VAPOR IMAGERY SUGGESTS THAT THE UPPER-LOW HAS PROBABLY PUSHED ABOUT AS FAR SOUTH AS IT CAN...WHICH WOULD SUPPORT THE GFS-GFDL-CANADIAN SCENARIO OF A MORE WESTWARD TRACK BY 96 HOURS. THE PAST 4 GFDL RUNS HAVE SUCCESSIVELY SHIFTED THE TRACK MORE WESTWARD WITH EACH RUN...WHILE THE GFS HAS A LEFT OF TRACK BIAS. THEREFORE...THE OFFICIAL TRACK WAS SHIFTED SLIGHTLY LEFT OF THE PREVIOUS FORECAST AND LEFT OF THE LATEST GFDL RUN...BUT NOT AS FAR WEST OR AS FAST AS THE GFS AND CANADIAN MODELS. FRANCES MAY BE ON A FAST-TRACK IN ITS DEVELOPMENT PROCESS...BUT I WOULD PREFER TO WAIT AND SEE IF ANY DRY AIR ON THE EAST SIDE GETS WRAPPED INTO THE CENTER. HOWEVER...IF A DISTINCT EYE APPEARS LATER TODAY...THEN RAPID INTENSIFICATION...AND ALSO MAKING FRANCES A MAJOR HURRICANE IN 48-72 HOURS LIKE THE GFDL AND SHIPS MODELS ARE INDICATING...WILL HAVE TO BE CONSIDERED ON THE NEXT ADVISORY. FORECASTER STEWART FORECAST POSITIONS AND MAX WINDS INITIAL 26/1500Z 13.1N 45.0W 60 KT 12HR VT 27/0000Z 14.0N 47.0W 70 KT 24HR VT 27/1200Z 15.2N 49.2W 80 KT 36HR VT 28/0000Z 16.4N 51.1W 90 KT 48HR VT 28/1200Z 17.5N 52.3W 95 KT 72HR VT 29/1200Z 18.6N 54.0W 95 KT 96HR VT 30/1200Z 20.0N 57.0W 95 KT 120HR VT 31/1200Z 21.0N 61.0W 95 KT |
