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Tropical Storm DANNY (Text)

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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
 
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FORECASTER BRENNAN
 
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