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| #536532 (Received by flhurricane at: 5:02 AM 24.Aug.2012) TCDAT4 TROPICAL STORM ISAAC DISCUSSION NUMBER 13 NWS NATIONAL HURRICANE CENTER MIAMI FL AL092012 500 AM EDT FRI AUG 24 2012 DATA FROM THE HURRICANE HUNTER AIRCRAFT INDICATE THAT ISAAC REMAINS POORLY ORGANIZED. WHILE THE 850-MB FLIGHT LEVEL CENTER WAS WELL SOUTH OF THE PREVIOUSLY ESTIMATED SURFACE CENTER LOCATION... DROPSONDE DATA SUGGEST THAT THE SURFACE CENTER REMAINS FARTHER NORTH. FLIGHT LEVEL AND SFMR WINDS SUPPORT MAINTAINING THE INTENSITY AT 40 KT FOR THIS ADVISORY...WHILE THE AIRCRAFT FOUND A MINIMUM PRESSURE OF 1000 MB. GIVEN THE CURRENT LACK OF ORGANIZATION OF THE INNER CORE...ONLY LIMITED STRENGTHENING IS FORECAST BEFORE THE CYCLONE BEGINS TO INTERACT WITH HISPANIOLA IN THE NEXT 24 HOURS. AFTER THAT TIME LITTLE CHANGE IS FORECAST AS ISAAC INTERACTS WITH PORTIONS OF CUBA. LATER IN THE PERIOD...ISAAC SHOULD HAVE AN OPPORTUNITY TO STRENGTHEN OVER THE STRAITS OF FLORIDA AND THE GULF OF MEXICO...AND THE NHC FORECAST IS CLOSE TO THE LGEM MODEL AT DAYS 4 AND 5. IT SHOULD BE NOTED THAT THERE IS SIGNIFICANT UNCERTAINTY IN TROPICAL CYCLONE INTENSITY PREDICTIONS AT 3 TO 5 DAYS. THE LONG TERM INITIAL MOTION ESTIMATE IS A HIGHLY UNCERTAIN 275/13...AS THE INITIAL POSITION ESTIMATE IS BASED ON A BLEND OF RECENT FIXES AND CONTINUITY. THE TRACK MODEL GUIDANCE CONTINUES TO BE IN GENERALLY GOOD AGREEMENT ON THE RESUMPTION OF A WEST- NORTHWESTWARD AND THEN NORTHWESTWARD MOTION IN THE NEXT 24 HOURS AS THE SUBTROPICAL RIDGE NORTH OF ISAAC WEAKENS. THIS GENERAL MOTION SHOULD CONTINUE THROUGH DAY 4...WHEN A TURN MORE TOWARD THE NORTH IS SHOWN AS A SHORTWAVE TROUGH AMPLIFIES OVER THE MISSISSIPPI VALLEY. LATE IN THE PERIOD THE TRACK MODEL GUIDANCE IS IN BETTER AGREEMENT ON THIS SCENARIO...AS THE ECMWF HAS TRENDED EASTWARD TOWARD THE REST OF THE MODELS THIS CYCLE. THE NEW NHC FORECAST HAS BEEN ADJUSTED ABOUT A DEGREE SOUTHWARD IN THE FIRST 12 HOURS DUE TO THE INITIAL POSITION AND MOTION...AND IS THEN BLENDED BACK TOWARD THE PREVIOUS TRACK BY 48 HOURS. AFTER THAT TIME...THE NHC FORECAST IS ESSENTIALLY AN UPDATE OF THE PREVIOUS ONE...AND IS BETWEEN THE ECMWF ON THE LEFT AND THE GFS AND TVCA CONSENSUS ON THE RIGHT. IT IS IMPORTANT NOT TO FOCUS ON THE EXACT TRACK DUE TO UNCERTAINTIES IN THE INITIAL LOCATION AND THE TRACK FORECAST...AND THE FACT THAT ISAAC HAS A LARGE AREA OF TROPICAL STORM FORCE WINDS ASSOCIATED WITH IT. FORECAST POSITIONS AND MAX WINDS INIT 24/0900Z 16.1N 70.0W 40 KT 45 MPH 12H 24/1800Z 17.0N 71.9W 50 KT 60 MPH 24H 25/0600Z 18.8N 74.1W 45 KT 50 MPH 36H 25/1800Z 20.6N 76.7W 45 KT 50 MPH...INLAND 48H 26/0600Z 22.4N 78.9W 45 KT 50 MPH...OVER WATER 72H 27/0600Z 25.0N 82.5W 55 KT 65 MPH 96H 28/0600Z 28.0N 86.0W 65 KT 75 MPH 120H 29/0600Z 30.5N 87.5W 75 KT 85 MPH...INLAND $$ FORECASTER BRENNAN |
