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| #536670 (Received by flhurricane at: 4:56 PM 24.Aug.2012) TCDAT4 TROPICAL STORM ISAAC DISCUSSION NUMBER 15 NWS NATIONAL HURRICANE CENTER MIAMI FL AL092012 500 PM EDT FRI AUG 24 2012 RECONNAISSANCE AIRCRAFT DATA INDICATE THAT THE CIRCULATION OF ISAAC HAS BECOME BETTER ORGANIZED THIS AFTERNOON...WITH A WELL-DEFINED AND MORE CIRCULAR INNER CIRCULATION. THE MAXIMUM 850 MB FLIGHT-LEVEL WINDS HAVE BEEN 70 KT...THE MAXIMUM RELIABLE SFMR SURFACE WIND ESTIMATE HAS BEEN 55 KT...AND THE MINIMUM REPORTED PRESSURE HAS BEEN 994 MB. BASED ON THESE DATA...THE INITIAL INTENSITY IS INCREASED TO 55 KT. ONE SIGN OF ONGOING ORGANIZATION ISSUES...HOWEVER...IS THE LACK OF PERSISTENCE OF THE INNER CORE CONVECTION...WHICH HAS WANED OVER THE PAST FEW HOURS. ISAAC HAS MADE ITS EXPECTED TURN TOWARD THE NORTHWEST AND THE INITIAL MOTION IS NOW 315/14. DURING THE FIRST 48-60 HR...THE TRACK GUIDANCE MADE AN EASTWARD SHIFT SINCE THE LAST ADVISORY. THIS WAS LED BY THE GFS...WHICH CHANGED TO A TRACK INTO THE SOUTHEASTERN GULF OF MEXICO TO LANDFALL IN SOUTHEASTERN FLORIDA. THE ECMWF AND UKMET ARE NOW ON THE LEFT EDGE OF THE GUIDANCE... SHOWING A TRACK ALONG THE NORTH COAST OF CUBA. THIS PART OF THE FORECAST TRACK IS SHIFTED EASTWARD BUT STILL LIES A LITTLE TO THE LEFT OF THE CENTER OF THE GUIDANCE ENVELOPE AND THE CONSENSUS MODELS. THERE REMAINS A SPREAD IN THE MODEL GUIDANCE AFTER 48 HR. THE GFS-BASED GUIDANCE SHOWS A NORTHEASTWARD MOTION AFTER LANDFALL ON THE NORTHERN GULF COAST...WHILE THE UKMET AND ECMWF SHOW A NORTHWARD MOTION. THE LATTER PART OF THE FORECAST TRACK IS SHIFTED EASTWARD CLOSE TO THE CONSENSUS MODELS. THE MAIN CONVECTIVE BAND AND STRONGEST WINDS NORTHEAST OF THE CENTER ARE MOVING INLAND AT THIS TIME. BASED ON THIS AND THE CURRENT LACK OF CONVECTION NEAR THE CENTER...LITTLE CHANGE IN STRENGTH IS EXPECTED BEFORE LANDFALL. THE INTENSITY FROM 12-48 HR WILL BE DETERMINED BY THE AMOUNT OF LAND INTERACTION. THE CURRENT FORECAST IS BASED ON THE PREMISE THAT ISAAC WILL REMAIN OVER LAND LONG ENOUGH TO ALLOW GRADUAL WEAKENING. HOWEVER...ANY CHANGE IN THE TRACK THAT ALLOWS IT TO REMAIN OVER WATER FOR A LONGER TIME COULD ALLOW IT TO BE STRONGER THAN FORECAST. AFTER 48 HR...THE ENVIRONMENTAL CONDITIONS APPEAR GENERALLY FAVORABLE FOR ISAAC TO STRENGTHEN INTO A HURRICANE OVER THE GULF OF MEXICO...AND THE INTENSITY FORECAST REFLECTS THIS. CONVERSELY...A LONGER TRACK OVER LAND MAY DISRUPT ISAAC ENOUGH TO BE UNABLE TO TAKE ADVANTAGE OF THESE FAVORABLE CONDITIONS. IT IS IMPORTANT NOT TO FOCUS ON THE EXACT TRACK DUE TO THE UNCERTAINTIES IN THE FORECAST AND THE FACT THAT ISAAC HAS A LARGE AREA OF TROPICAL STORM FORCE WINDS ASSOCIATED WITH IT. THE TROPICAL STORM WATCH FOR SOUTH FLORIDA AND THE FLORIDA KEYS MAY HAVE TO BE UPGRADED TO A HURRICANE WATCH IF THE INTENSITY FORECAST IS REVISED UPWARD. FORECAST POSITIONS AND MAX WINDS INIT 24/2100Z 17.2N 71.9W 55 KT 65 MPH 12H 25/0600Z 18.7N 73.6W 50 KT 60 MPH 24H 25/1800Z 20.7N 76.2W 50 KT 60 MPH...INLAND 36H 26/0600Z 22.4N 78.6W 45 KT 50 MPH...NEAR COAST OF CUBA 48H 26/1800Z 23.9N 80.7W 55 KT 65 MPH...OVER WATER 72H 27/1800Z 26.5N 84.0W 65 KT 75 MPH 96H 28/1800Z 29.5N 86.0W 75 KT 85 MPH 120H 29/1800Z 32.0N 86.0W 45 KT 50 MPH...INLAND $$ FORECASTER BEVEN |
