ZCZC MIATCDAT1 ALL TTAA00 KNHC DDHHMM TROPICAL STORM FLORENCE DISCUSSION NUMBER 13 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL062006 500 PM EDT WED SEP 06 2006 EVEN AS FLORENCE SHOWS SIGNS OF BECOMING BETTER ORGANIZED...THE CENTER REMAINS MADDENINGLY DIFFICULT TO TRACK. THE WELL-DEFINED LOW-CLOUD SWIRL HAS BEEN ROTATING NORTHWARD THIS AFTERNOON AROUND A PRESUMED BUT INVISIBLE OVERALL SYSTEM CENTER TO ITS WEST. AN 18 HOUR AVERAGE GIVES 295/8 FOR THE ADVISORY MOTION. THERE HAS BEEN NO CHANGE TO THE TRACK FORECAST REASONING...SO I'LL JUST PLAGIARIZE THIS MORNING'S DISCUSSION. THE KEY SYNOPTIC FEATURE IN THE SHORT TERM REMAINS THE UPPER LOW CENTERED A FEW HUNDRED MILES NORTHWEST OF FLORENCE. THIS COULD IMPART MORE OF A NORTHWARD TRACK OVER THE NEXT DAY OR SO...AS INDICATED BY THE GFDL MODEL...BUT THE REMAINING GUIDANCE IS TIGHTLY CLUSTERED ON A CONTINUED WEST-NORTHWESTWARD MOTION OVER THE NEXT THREE DAYS AS FLORENCE MOVES TO THE SOUTH OF THE MID-LEVEL SUBTROPICAL RIDGE. NEAR THE END OF THE FORECAST PERIOD...FLORENCE IS EXPECTED TO ROUND THE PERIPHERY OF THE RIDGE IN ADVANCE OF A DEEP-LAYER TROUGH OVER THE EASTERN UNITED STATES. MODEL GUIDANCE REMAINS IN EXCELLENT AGREEMENT ON A NORTHWARD TURN BY DAY 4. THE OFFICIAL FORECAST IS JUST AN UPDATE OF THE PREVIOUS ADVISORY...AND IS CLOSE TO A CONSENSUS OF THE WELL-CLUSTERED PRIMARY DYNAMICAL MODELS. THE MAJOR CHANGE IN ORGANIZATION TODAY IS THAT THE CONVECTION HAS BEEN GRADUALLY MIGRATING CLOSER TO THE CENTER OF CIRCULATION. OVER THE PAST COUPLE OF HOURS CONVECTION HAS ALSO BEEN INCREASING OVER THE NOW-OBSCURED CLOUD SWIRL...AND THIS MAY BE THE BEGINNING OF A MORE SUBSTANTIAL INTENSIFICATION. AS THE UPPER LOW MOVES WESTWARD...SHEAR WILL CONTINUE TO DECREASE AND THE ENVIRONMENT SHOULD BECOME MORE CONDUCIVE FOR DEVELOPMENT. GLOBAL MODELS AGREE ON DEVELOPING A LARGE ANTICYCLONE OVER FLORENCE IN THREE DAYS OR SO AND THE OFFICIAL FORECAST FOLLOWS A BLEND OF THE SHIPS AND GFDL GUIDANCE IN MAKING FLORENCE A MAJOR HURRICANE. TOWARD THE END OF THE FORECAST PERIOD...GUIDANCE IS ALSO IN GOOD AGREEMENT THAT FLORENCE...ALREADY A LARGE CYCLONE...WILL GET EVEN LARGER. FORECAST POSITIONS AND MAX WINDS INITIAL 06/2100Z 19.0N 51.4W 45 KT 12HR VT 07/0600Z 20.0N 53.0W 50 KT 24HR VT 07/1800Z 21.5N 55.5W 60 KT 36HR VT 08/0600Z 22.7N 58.2W 70 KT 48HR VT 08/1800Z 23.7N 60.7W 80 KT 72HR VT 09/1800Z 26.0N 65.0W 95 KT 96HR VT 10/1800Z 29.0N 67.0W 100 KT 120HR VT 11/1800Z 32.5N 67.0W 95 KT $$ FORECASTER FRANKLIN NNNN
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Page last modified: Monday, 11-Sep-2006 11:28:37 UTC