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| #372488 (Received by flhurricane at: 4:52 PM 30.Aug.2010) TCDAT3 TROPICAL STORM FIONA DISCUSSION NUMBER 1 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL082010 500 PM EDT MON AUG 30 2010 EARLIER TODAY...ABOUT 30 DROPSONDES WERE RELEASED DURING A G-V RESEARCH MISSION BEING CONDUCTED BY THE NATIONAL CENTER FOR ATMOSPHERIC RESEARCH NEAR THE AREA OF LOW PRESSURE LOCATED ABOUT 800 MILES EAST OF THE LESSER ANTILLES. ONE OF THE DROPSONDES MEASURED A SURFACE WIND OF 35 KT APPROXIMATELY 120 N MI TO THE NORTHEAST OF THE ESTIMATED CENTER. THIS MEASUREMENT AGREES WITH AN ASCAT PASS FROM 1208 UTC...WHICH SHOWED A SWATH OF 30-35 KT WINDS IN THAT SAME AREA. CONVECTION HAS BEEN A LITTLE THIN FOR MOST OF THE DAY...BUT BANDING FEATURES HAVE RECENTLY BECOME MORE PROMINENT MAINLY OVER THE WESTERN SEMICIRCLE. GIVEN THE INCREASE IN CONVECTION AND SINCE TROPICAL STORM FORCE WINDS ARE ALREADY OCCURRING...THE SYSTEM IS BEING DIRECTLY UPGRADED TO TROPICAL STORM FIONA. SINCE FIONA STILL LACKS SOME ORGANIZATION AND THE WIND FIELD IS SOMEWHAT LARGE...THE CYCLONE WILL LIKELY HAVE A DIFFICULT TIME INTENSIFYING OVER THE NEXT DAY OR SO. I DO NOT BELIEVE THIS STRUCTURE IS HANDLED WELL BY THE STATISTICAL INTENSITY GUIDANCE...WHICH INTENSIFY FIONA TO A HURRICANE IN 36 TO 48 HOURS...SO I AM INCLINED TO LEAN CLOSER TO THE DYNAMICAL GFDL AND HWRF AT THIS POINT. IN FACT...THE GFS DISSIPATES THE CYCLONE WITHIN 2 TO 3 DAYS. THE OFFICIAL FORECAST THEREFORE SHOWS MINIMAL STRENGTHENING OVER THE NEXT 1 TO 2 DAYS AND THEN LEVELS OUT THE INTENSITY FOR DAYS 3 THROUGH 5...WHEN IT APPEARS THAT INCREASING VERTICAL SHEAR COULD BECOME A LIMITING FACTOR. THE SURFACE CENTER HAS BEEN A LITTLE DIFFICULT TO LOCATE...AND THE INITIAL MOTION IS AN UNCERTAIN 270/21. TRACK MODEL GUIDANCE IS IN GOOD AGREEMENT FOR THE NEXT 48 HOURS AND SHOWS FIONA TURNING TOWARD THE NORTHWEST...GENERALLY FOLLOWING EARL AROUND THE WESTERN PERIPHERY OF THE SUBTROPICAL RIDGE. AFTER THAT...THE GFDL...HWRF...AND GFS KEEP FIONA AS A WEAK SYSTEM AND SHOW IT CONTINUING TO THE NORTH IN THE LOW-LEVEL FLOW BEHIND EARL. THE ECMWF...ON THE OTHER HAND...SHOWS A STRONGER FIONA AND SUGGESTS THAT THE SUBTROPICAL RIDGE COULD BUILD BACK TO THE WEST BEFORE THE CYCLONE CAN RECURVE. THE OFFICIAL FORECAST IS VERY CLOSE TO THE MODEL CONSENSUS TVCN FOR THE FIRST 48 HOURS BUT THEN LIES A LITTLE NORTH OF THE CONSENSUS IN FAVOR OF THE TRACKS OF THE WEAKER GFDL AND HWRF. FORECAST POSITIONS AND MAX WINDS INITIAL 30/2100Z 14.4N 48.7W 35 KT 12HR VT 31/0600Z 14.9N 51.9W 35 KT 24HR VT 31/1800Z 15.8N 55.9W 40 KT 36HR VT 01/0600Z 17.2N 59.2W 45 KT 48HR VT 01/1800Z 19.3N 62.0W 45 KT 72HR VT 02/1800Z 24.0N 66.0W 40 KT 96HR VT 03/1800Z 27.5N 68.0W 40 KT 120HR VT 04/1800Z 29.0N 69.0W 40 KT $$ FORECASTER BERG |
