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| #8133 (Received by flhurricane at: 11:07 AM 13.Sep.2004) TCDAT4 HURRICANE IVAN DISCUSSION NUMBER 45 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 11 AM EDT MON SEP 13 2004 THE INITIAL MOTION IS 310/07. THE LAST 4 RECON FIXES SUGGEST THAT IVAN HAS SLOWED A LITTLE AND HAS TURNED NORTHWESTWARD. THIS MAY JUST BE A TEMPORARY MOTION...BUT WITH INCREASING WEST TO NORTHWESTERLY 300 MB FLOW IMPINGING ON IVAN...THIS MAY TURN OUT TO BE MORE OF AN ESTABLISHED TREND. THE NHC MODEL GUIDANCE HAS SHIFTED SLIGHTLY WESTWARD...AND SO HAS THE OFFICIAL FORECAST TRACK. HOWEVER ...LATEST WATER VAPOR IMAGERY AND 12Z UPPER-AIR DATA INDICATE A 500 MB LOW OVER WESTERN TENNESSEE WITH A SHARP NORTH-SOUTH ORIENTED TROUGH EXTENDING SOUTHWARD INTO THE NORTH CENTRAL GULF OF MEXICO...WHICH HAS ERODED THE SUBTROPICAL RIDGE AXIS OVER THE CENTRAL AND EASTERN GULF. THIS HAS ALLOWED THE RIDGE ACROSS TEXAS AND LOUISIANA TO BUILD EASTWARD OVER THE WESTERN GULF. THE MID-LEVEL WIND FLOW ACROSS THE FLORIDA PENINSULA HAS ALSO VEERED FROM EASTERLY TO SOUTHERLY DURING THE PAST 24 HOURS...SUGGESTING THAT THE RIDGE HAS ERODED A LITTLE FARTHER EAST THAN THE NOGAPS AND GFDN MODELS HAVE BEEN FORECASTING. THEREFORE...THE FORECAST TRACK REMAINS ON THE EASTERN EDGE OF THE MODEL GUIDANCE ENVELOPE. THE LATEST AIR FORCE RESERVE RECON REPORT INDICATED THE PRESSURE HAD DROPPED ANOTHER 2 MB IN THE PAST 2 HOURS WHILE THE EYE DIAMETER HAS STABILIZED AT A RATHER LARGE 28-30 NMI. IT IS POSSIBLE THAT IVAN COULD STRENGTHEN ANOTHER 5 KT OR SO BEFORE INCREASING NORTHWESTERLY 300 MB SHEAR DISRUPTS THE INNER CORE CONVECTION. IN THE LONGER TERM...IVAN WILL BE MOVING OVER SSTS NEAR 30C...WITH THE SHEAR DECREASING AFTER 24 HOURS BEFORE IT PICKS UP AGAIN BY 48-60 HOURS. WHILE THE GULF WATERS ARE WARM...THE DEPTH OF THE WARM WATER IS RELATIVELY SHALLOW...EXCEPT FOR A WARM EDDY OVER THE NORTH-CENTRAL GULF. REGARDLESS...IVAN IS FORECAST TO BE A MAJOR HURRICANE AT U.S. LANDFALL. FORECASTER STEWART FORECAST POSITIONS AND MAX WINDS INITIAL 13/1500Z 20.6N 84.4W 140 KT 12HR VT 14/0000Z 21.5N 85.3W 140 KT 24HR VT 14/1200Z 23.2N 86.5W 135 KT 36HR VT 15/0000Z 25.2N 87.4W 130 KT 48HR VT 15/1200Z 27.2N 87.7W 120 KT 72HR VT 16/1200Z 31.0N 86.5W 100 KT...INLAND 96HR VT 17/1200Z 34.0N 84.5W 45 KT...INLAND 120HR VT 18/1200Z 36.5N 81.5W 25 KT...INLAND |
