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| #215606 (Received by flhurricane at: 11:11 AM 11.Sep.2008) TCDAT4 HURRICANE IKE DISCUSSION NUMBER 42 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL092008 1100 AM EDT THU SEP 11 2008 DATA FROM AIR FORCE AND NOAA AIRCRAFT INDICATE THAT IKE IS MAINTAINING AN ATYPICAL WIND STRUCTURE...CHARACTERIZED BY A VERY BROAD WIND FIELD WITH MULTIPLE WIND MAXIMA AND RELATIVELY LITTLE TRANSPORT OF WINDS ALOFT DOWN TO THE SURFACE. THE NOAA AIRCRAFT REPORTED MAXIMUM FLIGHT-LEVEL WINDS OF 103 KT 100 NMI NORTH-NORTHEAST OF THE CENTER...BUT SFMR AND DROPSONDE DATA INDICATE THAT THE SURFACE WINDS IN THAT AREA WERE ONLY AROUND 65 KT. IN FACT...THERE HAS BEEN NOTHING AT THE SURFACE RECENTLY THAT QUITE SUPPORTS THE CURRENT 85 KT ADVISORY INTENSITY. FORECASTING CHANGES IN THE WIND STRUCTURE OF TROPICAL CYCLONES IS EVEN MORE CHALLENGING THAN FORECASTING THE INTENSITY...BUT IKE HAS PLENTY OF TIME FOR ONE OF THE OUTER MAXIMA TO CONTRACT AND FOR THE WINDS TO TRY TO CATCH UP TO THE CENTRAL PRESSURE...CURRENTLY ABOUT 945 MB. ALTHOUGH OUTFLOW CONTINUES TO BE RESTRICTED TO THE NORTHWEST...IT IS STRONG ELSEWHERE AND THE SHEAR IS EXPECTED TO REMAIN LIGHT. ONE INHIBITING FACTOR COULD BE UPWELLING/MIXING OF COOLER WATER AHEAD OF THE PATH OF IKE DUE TO THE UNUSUALLY LARGE EXPANSE OF STRONG WINDS. THE OBJECTIVE GUIDANCE NEAR LANDFALL RANGES FROM A CATEGORY FOUR FROM THE GFDL TO CATEGORY TWO FROM THE SHIPS MODEL...ABOUT THE ERROR ONE CAN EXPECT FROM AN OFFICIAL FORECAST ONE TO TWO DAYS OUT. THE OFFICIAL FORECAST ROUGHLY SPLITS THE DIFFERENCE BETWEEN THESE GUIDANCE MODELS...AND ANTICIPATES THAT IKE WILL BE A MAJOR HURRICANE AT LANDFALL. THE INITIAL MOTION IS 290/9. THERE HAS BEEN LITTLE CHANGE TO THE TRACK FORECAST THINKING THROUGH LANDFALL...WITH IKE EXPECTED TO MAINTAIN A WEST-NORTHWESTWARD HEADING UNTIL VERY NEAR LANDFALL...WHEN IT SHOULD GENTLY TURN TO THE RIGHT AT THE WESTERN PERIPHERY OF THE SUBTROPICAL RIDGE. THE OFFICIAL FORECAST REMAINS NEAR THE MODEL CONSENSUS...WITH THE ECMWF ON THE RIGHT AND THE GFS TO THE LEFT. ONCE AGAIN...GIVEN THE TYPICAL FORECAST ERRORS FOR A 48 HOUR FORECAST...AND THE LARGE SIZE OF THE WIND FIELD...IT IS IMPORTANT NOT TO FOCUS ON THE EXACT FORECAST TRACK. FORECAST POSITIONS AND MAX WINDS INITIAL 11/1500Z 25.5N 88.4W 85 KT 12HR VT 12/0000Z 25.9N 90.0W 90 KT 24HR VT 12/1200Z 26.6N 92.0W 95 KT 36HR VT 13/0000Z 27.8N 94.2W 105 KT 48HR VT 13/1200Z 29.5N 95.9W 100 KT...INLAND 72HR VT 14/1200Z 34.5N 94.0W 35 KT...INLAND 96HR VT 15/1200Z 38.0N 85.0W 25 KT...EXTRATROPICAL 120HR VT 16/1200Z...ABSORBED $$ FORECASTER FRANKLIN |
