Tropical Storm FIONA

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TROPICAL STORM FIONA DISCUSSION NUMBER  12
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL082010
1100 AM AST THU SEP 02 2010
 
BURSTS OF CONVECTION CONTINUE TO FORM NEAR THE WELL-DEFINED
CIRCULATION OF FIONA THIS MORNING.  HOWEVER THIS CONVECTION HAS HAD
TROUBLE MAINTAINING ITSELF...PROBABLY DUE TO PERSISTENT NORTHERLY
SHEAR.  DVORAK CLASSIFICATIONS ARE UNCHANGED FROM EARLIER...SO THE
INITIAL INTENSITY WILL STAY 45 KT.
 
FIONA HAS TURNED TO THE RIGHT AND IS NOW MOVING 330/15.  AS THE
CYCLONE ROUNDS THE SOUTHWESTERN PERIPHERY OF A RIDGE OVER THE
CENTRAL ATLANTIC...IT IS EXPECTED TO TURN TOWARD THE NORTH AND
NORTHEAST BY LATE TOMORROW.  MOST OF THE MODEL GUIDANCE IS
CLUSTERED ON A TRACK NEAR OR WEST OF BERMUDA IN ABOUT 36-48
HRS...THOUGH WITH SOME SPEED DIFFERENCES.  SINCE FIONA HAS SHOWN NO
SIGNS OF SLOWING DOWN...AND WILL LIKELY REMAIN A WEAK SYSTEM
STEERED BY SWIFT LOW-LEVEL WINDS...THE NHC FORECAST WILL STAY
FASTER THAN THE MODEL CONSENSUS.  THE NEW FORECAST IS ALSO SHIFTED
A LITTLE TO THE RIGHT OF THE PREVIOUS ONE TO COME INTO BETTER
AGREEMENT WITH THE LATEST GUIDANCE.  THE GFDL SOLUTION OF A
SLOWER...MORE WESTWARD TRACK WELL TO THE SOUTHWEST OF BERMUDA IS
CONSIDERED UNLIKELY.
 
THE STORM IS WALKING A TIGHTROPE BETWEEN RATHER STRONG NORTHERLY
SHEAR TO ITS EAST AND AN AREA OF LIGHTER SHEAR FARTHER WEST.  WITH
THE RIGHTWARD SHIFT OF THE GUIDANCE THIS MORNING...THIS COULD CAUSE
EVEN STRONGER SHEAR IN A DAY OR SO NEAR THE CYCLONE.  ALL THE
GUIDANCE SHOWS A CONSIDERABLE WEAKENING OF FIONA...EXCEPT FOR THE
GFDL WHICH HAS AN UNREALISTIC TRACK FORECAST.  THE NHC INTENSITY
FORECAST IS REDUCED FROM THE PREVIOUS ONE...BUT IS STILL HIGHER
THAN NEARLY ALL OF THE GUIDANCE.

 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      02/1500Z 24.4N  65.8W    45 KT
 12HR VT     03/0000Z 26.4N  66.5W    45 KT
 24HR VT     03/1200Z 28.9N  66.7W    45 KT
 36HR VT     04/0000Z 31.3N  65.7W    40 KT
 48HR VT     04/1200Z 33.8N  64.1W    35 KT
 72HR VT     05/1200Z 37.9N  61.4W    25 KT...DISSIPATING
 96HR VT     06/1200Z...DISSIPATED
 
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FORECASTER BLAKE/PASCH
 
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