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| #8290 (Received by flhurricane at: 11:12 AM 14.Sep.2004) TCDAT4 HURRICANE IVAN DISCUSSION NUMBER 49 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 11 AM EDT TUE SEP 14 2004 RECONNAISSANCE REPORTS AND SATELLITE IMAGERY INDICATE THAT IVAN HAS WEAKENED SOMEWHAT THIS MORNING. THE CENTRAL PRESSURE IN THE CLOUD-FILLED EYE WAS UP TO 932 MB AND THE PEAK 700 MB WINDS HAVE COME DOWN TO 128 KT. BASED ON THESE OBSERVATIONS...THE ADVISORY INTENSITY IS LOWERED TO 120 KT AND EVEN THIS ESTIMATE IS PROBABLY A BIT HIGH. THIS WEAKENING IS CONCURRENT WITH THE EROSION OF THE EYEWALL REPORTED BY THE AIRCRAFT CREW AND THE DEVELOPMENT OF A NEW EYEWALL ABOUT 40-50 NM ACROSS. WATER VAPOR IMAGERY AND DATA FROM THE NOAA G-IV JET THIS MORNING CONTINUE TO INDICATE RESTRICTION OF THE OUTFLOW IN THE NORTHWEST QUADRANT OF THE HURRICANE...AS WELL AS VERY DRY AIR UNDERNEATH THE CIRRUS CANOPY. THIS...ALONG WITH THE CURRENT EYEWALL REPLACEMENT CYCLE...SUGGESTS THAT IVAN MAY CONTINUE TO WEAKEN A BIT DURING THE NEXT 12 HOURS OR SO. AFTER THAT...GLOBAL MODELS SUGGEST A RELAXATION OF THE WESTERLY SHEAR ABOUT THE TIME THAT IVAN IS EXPECTED TO PASS OVER A WARM EDDY IN THE CENTRAL GULF. THIS COULD ALLOW IVAN TO REGAIN SOME STRENGTH BEFORE LANDFALL...AND THIS IS REFLECTED IN THE OFFICIAL FORECAST. THERE HAS BEEN NO CHANGE FROM THE BASIC EXPECTATION THAT IVAN WILL BE A MAJOR HURRICANE AT LANDFALL. THE INITIAL MOTION IS 330/7. IVAN IS MOVING AROUND THE PERIPHERY OF THE ATLANTIC SUBTROPICAL RIDGE. A SECOND MID-LEVEL HIGH IS CENTERED OVER LOUISIANA WITH A RIDGE EXTENDING SOUTHWARD INTO THE WESTERN GULF OF MEXICO. 12Z RAOBS AND JET DATA INDICATE THAT THIS LATTER RIDGE IS A LITTLE STRONGER THAN FORECAST BY THE 6Z GFS RUN. THIS MIGHT RESULT IN WEAKER STEERING AND A SLOWER MOTION TOWARD THE COAST THAN THE GFS IS FORECASTING. MODEL GUIDANCE IS IN PRETTY GOOD AGREEMENT THROUGH 48 HOURS...WITH ONLY ABOUT 125 MILES SEPARATING THE LANDFALLS OF THE ECMWF TO THE WEST OF THE OFFICIAL FORECAST FROM THE UKMET TO ITS EAST. THE OFFICIAL FORECAST HAS BEEN SHIFTED SLIGHTLY WEST AND IS IN BEST AGREEMENT WITH THE FSU SUPERENSEMBLE...WHICH HAS PERFORMED WELL WITH THIS STORM. THERE IS CONSIDERABLE SPREAD IN THE MODEL FORECASTS AFTER LANDFALL...AND IT IS POSSIBLE THAT THE REMNANTS OF IVAN WILL MOVE VERY SLOWLY OR STALL NEAR OR OVER THE APPALACHIANS IN 4 OR 5 DAYS...WHICH WOULD PRODUCE A VERY SERIOUS FLOODING EVENT. FORECASTER FRANKLIN FORECAST POSITIONS AND MAX WINDS INITIAL 14/1500Z 23.4N 86.2W 120 KT 12HR VT 15/0000Z 24.4N 86.9W 115 KT 24HR VT 15/1200Z 26.3N 88.0W 115 KT 36HR VT 16/0000Z 28.5N 88.5W 120 KT 48HR VT 16/1200Z 30.5N 88.5W 110 KT...INLAND 72HR VT 17/1200Z 34.0N 86.5W 40 KT...INLAND 96HR VT 18/1200Z 36.0N 84.0W 20 KT...INLAND 120HR VT 19/1200Z 36.5N 83.0W 20 KT...INLAND |
