ZCZC MIATCDAT5 ALL TTAA00 KNHC DDHHMM TROPICAL STORM DANNY DISCUSSION NUMBER 9 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL052009 1100 AM EDT FRI AUG 28 2009 THE CENTER OF DANNY REMAINS EXPOSED THIS MORNING...AND OVER THE PAST COUPLE OF HOURS HAS BEEN MOVING ALMOST DUE WESTWARD AWAY FROM THE DEEP CONVECTION. NOAA BUOY 41047 WELL SOUTHEAST OF THE CENTER REPORTED A 1-MINUTE PEAK SUSTAINED WIND OF 31 KT AT 1100 UTC. THE INITIAL INTENSITY IS HELD AT 35 KT...ASSUMING THAT HIGHER WINDS STILL EXIST WELL EAST OF THE CENTER. AN AIR FORCE RESERVE HURRICANE HUNTER AIRCRAFT WILL BE INVESTIGATING DANNY LATER THIS AFTERNOON TO PROVIDE MORE INFORMATION ON ITS INTENSITY AND STRUCTURE. THE INITIAL MOTION ESTIMATE IS 325/9...A COMPROMISE BETWEEN THE SHORT TERM WESTWARD MOTION AND THE LONGER TERM NORTH-NORTHWESTWARD MOTION OBSERVED OVERNIGHT. THE FORECAST IS ADJUSTED TOWARD THE WEST DUE TO THE INITIAL MOTION AND ACTUALLY LIES WEST OF ALL THE DYNAMICAL MODELS AT 12 HOURS...AS THESE MODELS IMMEDIATELY TURN DANNY NORTHWARD. LATER IN THE FORECAST PERIOD...THE TRACK IS VERY CLOSE TO THE TVCN MULTI-MODEL CONSENSUS. BY 36 HOURS...THIS POSITION IS JUST SOUTH OF THE COAST OF MASSACHUSETTS...WITH THE GFS...ECMWF...AND GFS ENSEMBLE MEAN SIGNIFICANTLY LEFT OF THE CONSENSUS...AND MOST OF THE OTHER GUIDANCE CLUSTERED TO THE RIGHT. BEYOND THAT TIME...DANNY SHOULD BE ACCELERATING TOWARD THE NORTHEAST THROUGH THE CANADIAN MARITIMES AND EAST-NORTHEASTWARD INTO THE NORTH ATLANTIC. IT SHOULD BE NOTED THAT THERE ARE A COUPLE OF ALTERNATIVE SCENARIOS THAT COULD OCCUR. THE SHALLOW BAM MODEL REPRESENTS AN EVEN MORE WESTWARD TRACK THAT COULD OCCUR IF DANNY LOSES ALL OF ITS DEEP CONVECTION. IT IS ALSO POSSIBLE THAT A NEW CENTER COULD RE-FORM UNDER THE DEEP CONVECTION FARTHER EAST. EITHER OF THESE SCENARIOS WOULD LIKELY REDUCE THE THREAT TO THE U.S. EAST COAST. THE INTENSITY FORECAST SHOWS THE POSSIBILITY FOR A LITTLE STRENGTHENING IN THE NEXT 12 HOURS...BUT AFTER THAT TIME THE CYCLONE WILL BE MOVING INTO A VERY UNFAVORABLE ENVIRONMENT...WITH THE SHIPS MODEL SHOWING WIND SHEAR INCREASING TO OVER 30 KT BY 24 HOURS AS DANNY INTERACTS WITH A DEEP-LAYER TROUGH OVER THE EASTERN UNITED STATES. THE GLOBAL MODELS AND PHASE SPACE DIAGRAMS SHOW THAT DANNY WILL BEGIN EXTRATROPICAL TRANSITION BEGINNING BY 48 HOURS...AND THAT THE CYCLONE WILL BE FULLY EXTRATROPICAL BY 72 HOURS. THIS EVOLUTION IS REFLECTED IN THE OFFICIAL FORECAST...WHICH SHOWS AN EXPANDING WIND FIELD AS DANNY MOVES FROM THE CANADIAN MARITIMES INTO THE NORTH ATLANTIC. DESPITE THE WESTWARD SHIFT IN THE TRACK...A TROPICAL STORM WARNING WILL NOT BE ISSUED FOR THE COAST OF NORTH CAROLINA AT THIS TIME...DUE TO THE CURRENT AND EXPECTED LIMITED EXTENT OF TROPICAL STORM FORCE WINDS ON THE WEST SIDE OF THE CIRCULATION. THE TROPICAL STORM WATCH REMAINS IN EFFECT IN CASE THE WIND FIELD BECOMES BETTER DEFINED ON THE WESTERN SIDE OF DANNY OR IF THE FORECAST CONTINUES TO SHIFT WESTWARD. A TROPICAL STORM WATCH MAY ALSO BE NEEDED FOR PORTIONS OF THE COAST OF NEW ENGLAND LATER TODAY. FORECAST POSITIONS AND MAX WINDS INITIAL 28/1500Z 30.1N 75.5W 35 KT 12HR VT 29/0000Z 32.5N 75.7W 40 KT 24HR VT 29/1200Z 36.2N 74.1W 40 KT 36HR VT 30/0000Z 40.7N 70.7W 40 KT 48HR VT 30/1200Z 44.6N 65.1W 40 KT...INLAND 72HR VT 31/1200Z 49.6N 52.5W 40 KT...EXTRATROPICAL 96HR VT 01/1200Z 52.5N 38.0W 40 KT...EXTRATROPICAL 120HR VT 02/1200Z 54.5N 21.5W 45 KT...EXTRATROPICAL $$ FORECASTER BRENNAN NNNN
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Page last modified: Thursday, 31-Dec-2009 12:09:08 UTC