ZCZC MIATCDAT3 ALL TTAA00 KNHC DDHHMM HURRICANE ISABEL DISCUSSION NUMBER 29 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL 5 AM EDT SAT SEP 13 2003 THE MUCH ANTICIPATED WEAKENING HAS OCCURRED. DATA FROM A RECONNAISSANCE PLANE INDICATE THAT THE CENTRAL PRESSURE HAS RISEN TO 935 MB AND FLIGHT-LEVEL PEAK WINDS ARE 139 KNOTS. INITIAL INTENSITY HAS BEEN LOWERED TO 130 KNOTS AND THIS IS PROBABLY ON THE HIGH SIDE. THE RECON ALSO CONFIRMED THE PRESENCE OF TWO CONCENTRIC EYEWALLS OF 25 AND 35 NMI AND A BAND OF MAXIMUM WINDS ASSOCIATED WITH EACH EYEWALL...RESPECTIVELY. THERE IS NO SKILL IN PREDICTING IF THE CURRENT EYEWALL CYCLE WILL RESULT IN FURTHER WEAKENING OR IN ANOTHER ROUND OF INTENSIFICATION. BEST BET IS TO INDICATE SOME FLUCTUATIONS IN INTENSITY IN THE NEXT DAY OR TWO WITH A WEAKENING TREND DUE TO COOLER SSTS OR SHEAR THEREAFTER. NEVERTHERELESS... ISABEL IS EXPECTED TO REMAIN A MAJOR HURRICANE THROUGHOUT THE FORECAST PERIOD. ISABEL IS MOVING TOWARD THE WEST OR 280 DEGREES AT 8 KNOTS AROUND THE PERIPHERY OF A STRONG DEEP-LAYER ANTICYCLONE. THIS PATTERN IS EXPECTED TO STEER THE HURRICANE TOWARD THE WEST WITH A GRADUAL TURN TO THE WEST-NORTHWEST AS INDICATED IN THE OFFICIAL FORECAST. IT APPEARS THAT THE TROUGH WHICH IS CURRENTLY ERODING THE WESTERN PORTION OF THE RIDGE WILL WEAKEN AND THE HIGH WILL EXPAND WESTWARD. THIS EXPANSION OF THE RIDGE WILL CONTROL HOW CLOSE ISABEL APPROACHES THE U.S EAST COAST. HIGH UNCERTAINTIES CONTINUE AT LONGER RANGE. THE CONSISTENT AND GOOD PERFORMER UK MODEL HAS THE HURRICANE NEAR THE COAST OF NORTH CAROLINA BETWEEN 5 AND 6 DAYS. ON THE OTHER HAND...THE RELIABLE GFDL TURNS ISABEL NORTHWARD IN FIVE DAYS AT A GOOD DISTANCE AWAY FROM THE U.S EAST COAST. BECAUSE BOTH MODELS HAVE BEEN VERY GOOD SO FAR...THE OFFICIAL FORECAST IS IN BETWEEN THESE TWO MODELS. AT THIS TIME...I WOULD NOT EVEN DISCUSS THE GFS WHICH MOVES THE HURRICANE EASTWARD FOR THE FIRST 12 TO 18 HOURS IN THE LATEST 00Z RUN AND ISABEL IS ALREADY WEST OF 60 DEGREES WEST. HOWEVER...THE LARGE SCALE PATTERN PROVIDED BY THE GFS IS QUITE REASONABLE. NOTE: THERE ARE NO DYNAMICAL MODELS SUGGESTING THAT ISABEL MIGHT EVER REACH FLORIDA. FORECASTER AVILA FORECAST POSITIONS AND MAX WINDS INITIAL 13/0900Z 22.0N 60.4W 130 KT 12HR VT 13/1800Z 22.2N 61.6W 130 KT 24HR VT 14/0600Z 23.0N 63.7W 130 KT 36HR VT 14/1800Z 23.5N 65.5W 130 KT 48HR VT 15/0600Z 24.5N 67.5W 130 KT 72HR VT 16/0600Z 26.0N 70.0W 120 KT 96HR VT 17/0600Z 28.5N 72.0W 115 KT 120HR VT 18/0600Z 32.0N 74.5W 105 KT NNNN
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Page last modified: Monday, 07-Feb-2005 16:49:58 UTC