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| #536405 (Received by flhurricane at: 4:56 PM 23.Aug.2012) TCDAT4 TROPICAL STORM ISAAC DISCUSSION NUMBER 11 NWS NATIONAL HURRICANE CENTER MIAMI FL AL092012 500 PM AST THU AUG 23 2012 LOCATING THE CENTER OF ISAAC IS A BIT PROBLEMATIC THIS AFTERNOON. WHILE THE CYCLONE HAS A LARGE AND WELL-DEFINED OUTER CIRCULATION...THE INNER CORE HAS NOT CONSOLIDATED AND THERE ARE STILL MULTIPLE VORTICITY CENTERS ROTATING AROUND THE MEAN CENTER. HIGHLIGHTING THE ISSUE ARE DATA FROM NOAA BUOY 42059...WHICH HAS REPORTED 25-30 KT SOUTHWESTERLY WINDS AT A POSITION SOUTHWEST OF THE LATEST HURRICANE HUNTER AIRCRAFT FIXES...WHICH IN TURN WERE SOUTH OF THE CENTER TRACKED IN THE PREVIOUS ADVISORY. THE INITIAL POSITION IS A BLEND OF ALL THESE FEATURES. THE INITIAL INTENSITY REMAINS 35 KT BASED ON THE HURRICANE HUNTER DATA. THE SOMEWHAT UNCERTAIN INITIAL MOTION IS 285/14. THE TRACK MODEL GUIDANCE IS IN GOOD AGREEMENT THAT ISAAC SHOULD MOVE GENERALLY WEST-NORTHWESTWARD FOR THE NEXT 48-72 HR...AND THIS PART OF THE NEW FORECAST TRACK IS VERY SIMILAR TO THE PREVIOUS TRACK. AFTER THAT TIME...THE GUIDANCE HAS SHIFTED A LITTLE WESTWARD IN RESPONSE TO THE GLOBAL MODELS FORECASTING THE WEAKNESS IN THE SUBTROPICAL RIDGE TO BE SOMEWHAT FARTHER WEST THAN BEFORE. THE ECMWF IN PARTICULAR HAS MADE A SIGNIFICANT SHIFT...SHOWING A WEST-NORTHWESTWARD MOTION INTO THE CENTRAL GULF OF MEXICO BY DAY 5. DESPITE THE GENERAL WESTWARD SHIFT...THE HWRF AND CANADIAN MODELS STILL CALL FOR ISAAC TO MOVE UP THE FLORIDA PENINSULA. THUS... SIGNIFICANT UNCERTAINTY REMAINS ABOUT THE THREAT ISAAC POSES TO FLORIDA AND OTHER PORTIONS OF THE GULF COAST. THE 96-120 HR POINTS HAVE BEEN SHIFTED A LITTLE WESTWARD FROM THE PREVIOUS ADVISORY AND LIE NEAR THE CENTER OF THE GUIDANCE ENVELOPE AND THE CONSENSUS MODELS. IN THE SHORT TERM...THE STRUCTURE OF ISAAC SUGGESTS THAT ONLY SLOW STRENGTHENING IS LIKELY. HOWEVER...THE ENVIRONMENTAL CONDITIONS ARE FAVORABLE FOR RAPID INTENSIFICATION...WHICH COULD OCCUR IF THE CYCLONE DEVELOPS A WELL-DEFINED INNER CORE. WHILE THE OFFICIAL FORECAST NO LONGER SHOWS IT...ISAAC COULD REACH HURRICANE INTENSITY ABOUT THE TIME IT MAKES LANDFALL IN HISPANIOLA BETWEEN 24-36 HR. AFTER THAT...PASSAGE OVER HISPANIOLA AND CUBA SHOULD CAUSE SOME WEAKENING. THE INTENSITY FORECAST SHOWS STRENGTHENING OVER THE GULF OF MEXICO...AND THE CURRENT 120 HR INTENSITY COULD BE CONSERVATIVE IF THE GLOBAL MODEL UPPER-LEVEL WIND FORECASTS VERIFY. THE NEW INTENSITY FORECAST IS SIMILAR TO THE PREVIOUS FORECAST AND REMAINS STRONGER THAN THE INTENSITY CONSENSUS. THE NOAA G-IV JET AND AN AIR FORCE RESERVE HURRICANE HUNTER AIRCRAFT ARE CURRENTLY CONDUCTING A SYNOPTIC SURVEILLANCE MISSION AROUND ISAAC. THE DATA WILL BE AVAILABLE FOR THE 0000 UTC MODEL RUNS. FORECAST POSITIONS AND MAX WINDS INIT 23/2100Z 16.0N 67.1W 35 KT 40 MPH 12H 24/0600Z 16.6N 69.0W 40 KT 45 MPH 24H 24/1800Z 17.5N 71.5W 50 KT 60 MPH 36H 25/0600Z 18.9N 74.0W 60 KT 70 MPH 48H 25/1800Z 20.3N 76.2W 55 KT 65 MPH...INLAND 72H 26/1800Z 23.0N 80.0W 50 KT 60 MPH...OVER WATER 96H 27/1800Z 25.5N 83.0W 65 KT 75 MPH 120H 28/1800Z 28.5N 85.5W 75 KT 85 MPH $$ FORECASTER BEVEN |
