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| #112227 (Received by flhurricane at: 10:49 AM 21.Sep.2006) TCDAT3 HURRICANE HELENE DISCUSSION NUMBER 37 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL082006 1100 AM EDT THU SEP 21 2006 THE OVERALL CLOUD PATTERN HAS CONTINUED TO DETERIORATE WITH THE COLDEST CONVECTIVE CLOUD TOPS LOCATED PRIMARILY OVER THE EASTERN SEMICIRCLE OF HELENE. CONSEQUENTLY...DVORAK DATA T-NUMBERS HAVE DECREASED. USING A BLEND OF THE DVORAK DATA T...AND CURRENT INTENSITY NUMBERS YIELDS AN INITIAL INTENSITY ESTIMATE OF 70 KT. AS MENTIONED IN THE PREVIOUS DISCUSSION...IT APPEARS THAT SOME MID-LEVEL SHEAR IS AFFECTING THE HURRICANE. DURING THE NEXT COUPLE OF DAYS... THE SHEAR IS FORECAST TO INCREASE AND HELENE WILL BE MOVING OVER SLIGHTLY COOLER SSTS. ACCORDINGLY...THE SHIPS AND FSU SUPERENSEMBLE DO NOT RESTRENGTHEN HELENE AND THE OFFICIAL FORECAST WILL NOT EITHER. THE NHC INTENSITY FORECAST FOLLOWS THE FSU SUPERENSEMBLE CLOSELY THROUGH 72 HOURS...THEREAFTER IT IS A LITTLE HIGHER THAN THE GUIDANCE AS HELENE IS EXPECTED TO BECOME A POWERFUL EXTRATROPICAL CYCLONE. THE INITIAL MOTION ESTIMATE IS 005/11. HELENE IS CURRENTLY ROUNDING THE WESTERN PERIPHERY OF THE SUBTROPICAL RIDGE LOCATED WELL EAST OF THE HURRICANE. HELENE IS FORECAST BY THE DYNAMICAL MODELS TO ACCELERATE NORTHEASTWARD AHEAD OF A LARGE DEEP-LAYER TROUGH THAT IS MOVING OFF THE UNITED STATES EAST COAST. THE GFDL REMAINS ON THE WESTERN SIDE OF THE GUIDANCE WHILE THE UKMET AND ECMWF ARE ON THE EASTERN SIDE. THE OFFICIAL TRACK FORECAST IS IS VERY CLOSE TO THE PREVIOUS ADVISORY...WHICH IS CLOSE TO THE GFS...NOGAPS...AND FLORIDA STATE SUPERENSEMBLE. EVEN THOUGH HELENE IS FORECAST TO RECURVE OVER THE CENTRAL ATLANTIC OCEAN...SOME LONG PERIOD SWELLS COULD AFFECT PORTIONS OF THE EAST COAST OF NORTH AMERICA AND BERMUDA DURING THE NEXT COUPLE OF DAYS. FORECAST POSITIONS AND MAX WINDS INITIAL 21/1500Z 29.6N 56.9W 70 KT 12HR VT 22/0000Z 31.4N 56.3W 70 KT 24HR VT 22/1200Z 34.1N 54.5W 70 KT 36HR VT 23/0000Z 36.8N 51.2W 70 KT 48HR VT 23/1200Z 39.6N 46.6W 65 KT...BECOMING EXTRATROPICAL 72HR VT 24/1200Z 45.2N 36.4W 60 KT...EXTRATROPICAL 96HR VT 25/1200Z 49.5N 28.5W 60 KT...EXTRATROPICAL 120HR VT 26/1200Z 54.0N 20.0W 55 KT...EXTRATROPICAL $$ FORECASTER BROWN/AVILA |
