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| #531866 (Received by flhurricane at: 10:53 PM 04.Aug.2012) TCDAT1 TROPICAL STORM FLORENCE DISCUSSION NUMBER 5 NWS NATIONAL HURRICANE CENTER MIAMI FL AL062012 1100 PM AST SAT AUG 04 2012 FLORENCE IS BECOMING BETTER ORGANIZED. BANDING FEATURES ASSOCIATED WITH THE CYCLONE HAVE RECENTLY DISSIPATED IN FAVOR OF A CENTRAL DENSE OVERCAST. EARLIER TRMM AND WINDSAT OVERPASSES REVEAL A WELL- DEFINED LOW-LEVEL STRUCTURE UNDERNEATH THIS NEW CONVECTIVE MASS... WITH A NEARLY CLOSED RING OF CONVECTION NOW PRESENT. A DVORAK INTENSITY ESTIMATE OF 3.5/55 KT FROM TAFB AT 0000 UTC AND THREE- HOURLY AVERAGED ADT VALUES OF AROUND 3.3 ARE THE BASIS FOR INCREASING THE INITIAL INTENSITY TO 50 KT FOR THIS ADVISORY. THE INTENSITY FORECAST IS TRICKY. DESPITE BEING IN A LOW-SHEAR ENVIRONMENT...FLORENCE IS FORECAST TO MOVE THROUGH A TONGUE OF MARGINALLY WARM WATERS OVER THE NEXT COUPLE OF DAYS. IN ADDITION... EUMETSAT RGB SATELLITE IMAGERY INDICATES THAT THE CYCLONE IS SURROUNDED BY A RATHER DRY AIR MASS...AND THIS AIR MASS SHOULD ACCOMPANY FLORENCE ON ITS WESTWARD TREK. THESE NEGATIVE FACTORS SUGGEST THAT ANY STRENGTHENING IN THE SHORT TERM WOULD NOT LIKELY BE SIGNIFICANT. BEYOND 72 HOURS...GLOBAL MODELS SHOW FLORENCE ENCOUNTERING INCREASING SOUTHWESTERLY SHEAR ASSOCIATED WITH AN UPPER-LEVEL TROUGH OVER THE CENTRAL ATLANTIC. EVEN THOUGH THE STORM WILL BE MOVING OVER WARMER WATERS BY THIS TIME...THE SHEAR SHOULD BE STRONG ENOUGH TO INDUCE WEAKENING. THE NEW NHC INTENSITY FORECAST IS ADJUSTED UPWARD THROUGH 48 HOURS BASED ON CURRENT TRENDS AND IS ABOUT THE SAME AS THE PREVIOUS FORECAST AFTER THAT TIME. THE FORECAST IS IN EXCELLENT AGREEMENT WITH THE LATEST SHIPS/LGEM OUTPUT. THE INITIAL MOTION ESTIMATE IS 295/13. A MID-LEVEL RIDGE OVER THE EASTERN ATLANTIC IS EXPECTED TO BUILD WESTWARD DURING THE NEXT SEVERAL DAYS...WHICH WILL CAUSE THE TRACK OF FLORENCE TO BEND TOWARD THE WEST. LATE IN THE FORECAST PERIOD...THE CYCLONE IS EXPECTED TO ENCOUNTER A WEAKNESS IN THE SUBTROPICAL RIDGE OVER THE CENTRAL ATLANTIC WHICH SHOULD INDUCE A WEST-NORTHWESTERLY HEADING. ALTHOUGH THE SPREAD IN THE TRACK GUIDANCE HAS DECREASED THIS CYCLE...IT REMAINS FAIRLY SIGNIFICANT BEYOND 72 HOURS. THE DIFFERENCE IN TRACK SOLUTIONS AT LATER TIMES APPEARS DEPENDENT ON THE VERTICAL DEPTH/ STRENGTH OF THE CYCLONE...WITH THE ECMWF/GFDL/HWRF FORECASTING A WEAKER VERSION OF FLORENCE AND THE GFS FAVORING A STRONGER SYSTEM. THE NEW NHC FORECAST TRACK REMAINS IN BETWEEN THESE TWO EXTREMES BUT HAS BEEN ADJUSTED TOWARD THE CAMP OF MODELS FAVORING A WEAKER CYCLONE GIVEN THE SHEAR FORECAST. FORECAST POSITIONS AND MAX WINDS INIT 05/0300Z 16.1N 33.0W 50 KT 60 MPH 12H 05/1200Z 16.5N 34.8W 55 KT 65 MPH 24H 06/0000Z 17.0N 37.2W 60 KT 70 MPH 36H 06/1200Z 17.5N 39.7W 60 KT 70 MPH 48H 07/0000Z 18.1N 42.6W 60 KT 70 MPH 72H 08/0000Z 19.3N 49.0W 45 KT 50 MPH 96H 09/0000Z 20.9N 55.1W 35 KT 40 MPH 120H 10/0000Z 23.5N 60.5W 30 KT 35 MPH...POST-TROP/REMNT LOW $$ FORECASTER KIMBERLAIN |
