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| #152512 (Received by flhurricane at: 4:40 AM 26.Sep.2007) TCDAT2 TROPICAL STORM KAREN DISCUSSION NUMBER 6 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL122007 500 AM EDT WED SEP 26 2007 AFTER LOOKING RATHER ANEMIC YESTERDAY...KAREN IS FINALLY STARTING TO PRODUCE PRODUCE DEEP CONVECTION NEAR THE CENTER AND MICROWAVE DATA SUGGEST THE EARLY STAGES OF AN INNER CORE. SATELLITE INTENSITY ESTIMATES HAVE RISEN AND THE INITIAL INTENSITY IS INCREASED TO 45 KT. KAREN IS MOVING RIGHT ALONG THE PREVIOUS FORECAST TRACK WITH AN INITIAL MOTION OF 280/11. THE CYCLONE IS EXPECTED TO GRADUALLY TURN NORTHWESTWARD OVER THE NEXT COUPLE OF DAYS AS A SMALL WEAKNESS DEVELOPS IN THE DEEP-LAYER SUBTROPICAL RIDGE OVER THE CENTRAL ATLANTIC. THEREAFTER...THE GLOBAL MODELS DIFFER IN THEIR FORECAST OF A LARGE MIDDLE-UPPER LEVEL TROUGH EXPECTED TO DEVELOP OVER THE WESTERN ATLANTIC. THE NOGAPS...GFDN...AND HWRF MODEL SHOW THIS TROUGH REMAINING IN PLACE LONG ENOUGH TO KEEP THE CYCLONE MOVING NORTHWESTWARD THROUGHOUT THE ENTIRE FORECAST PERIOD. CONVERSELY... THE UKMET QUICKLY LIFTS THE SAME TROUGH NORTHWARD BEYOND 72 HOURS ALLOWING THE CYCLONE TO TURN WESTWARD UNDER THE INFLUENCE OF A DEVELOPING WEST ATLANTIC RIDGE. THE GFS IS BETWEEN THESE TWO SOLUTIONS AS IT SHOWS THE TROUGH SIMILARLY LIFTING NORTHWARD BUT WITH A MUCH WEAKER RIDGE IN ITS WAKE. THIS PATTERN WOULD KEEP THE CYCLONE MOVING GENERALLY NORTHWESTWARD...ALBEIT VERY SLOWLY. THE OFFICIAL FORECAST LEANS TOWARD THE GFS SOLUTION BASED ITS PAST PERFORMANCE AND IS A LITTLE TO THE LEFT OF THE DYNAMICAL MODEL CONSENSUS. THIS FORECAST IS ALSO CLOSE TO THE FSU SUPERENSEMBLE. WITH THE RECENT DEVELOPMENT OF CONVECTION NEAR THE CENTER AND GENERALLY FAVORABLE ENVIRONMENTAL CONDITIONS...KAREN SHOULD STRENGTHEN DURING THE NEXT DAY OR TWO. THEREAFTER...THE INTENSITY FORECAST BECOMES HIGHLY PROBLEMATIC DUE TO THE POSSIBLE DEVELOPMENT OF UNFAVORABLE UPPER-LEVEL WINDS. THE GLOBAL MODELS SHOW STRONG WESTERLY FLOW IMPINGING UPON THE CYCLONE IN A DAY OR TWO. HOWEVER...NEITHER THE GFDL NOR THE HWRF MODELS RESPOND TO THE SHEAR AND CONTINUE TO STRENGTHEN KAREN THROUGHOUT THE FORECAST. IN FACT...THE HWRF MODEL MAKES KAREN A CATEGORY 2 HURRICANE BY DAY 5. SINCE SUCH ROBUST DEVELOPMENT SEEMS QUESTIONABLE GIVEN THE EXPECTED INCREASE IN VERTICAL SHEAR...THE OFFICIAL FORECAST IS BASED MORE ON THE SHIPS AND LGEM MODELS WHICH SHOW KAREN REACHING MINIMAL HURRICANE STRENGTH IN A DAY OR TWO FOLLOWED BY SLIGHT WEAKENING. FORECAST POSITIONS AND MAX WINDS INITIAL 26/0900Z 11.2N 42.1W 45 KT 12HR VT 26/1800Z 11.9N 43.9W 55 KT 24HR VT 27/0600Z 13.0N 46.1W 60 KT 36HR VT 27/1800Z 14.3N 48.0W 65 KT 48HR VT 28/0600Z 15.6N 49.4W 65 KT 72HR VT 29/0600Z 18.0N 51.5W 60 KT 96HR VT 30/0600Z 20.0N 53.0W 55 KT 120HR VT 01/0600Z 22.5N 55.0W 55 KT $$ FORECASTER RHOME |
