Tropical Storm HANNA

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TROPICAL STORM HANNA DISCUSSION NUMBER  32
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL082008
500 PM EDT THU SEP 04 2008
 
THE RECONNAISSANCE AIRCRAFT INVESTIGATING HANNA IS FINDING THE
CIRCULATION CENTER AT 850 MB DISPLACED TO THE NORTHWEST OF THE MEAN
CENTER OF ROTATION APPARENT IN THE LOW CLOUD LINES.  THERE ARE ALSO
MULTIPLE SWIRLS...BUT IT DOES APPEAR THAT THE LOW-LEVEL CENTER HAS
JUMPED A LITTLE BIT TO THE WEST IN RESPONSE TO THE CONVECTIVE
ASYMMETRY.  ALTHOUGH A COUPLE MORE SHIFTS ARE POSSIBLE...THE
ORIENTATION OF THE SHEAR SHOULD TURN MORE SOUTHERLY WITH
TIME...THAT IS...MORE ALONG THE TRACK...AND THEN HAVE LESS OF AN
IMPACT ON THE TRACK.  THE BASIC FORECAST PHILOSOPHY IS UNCHANGED. 
THE NEW TRACK FORECAST IS VERY CLOSE TO THE PREVIOUS ONE WITH ONLY
A SLIGHT LEFTWARD SHIFT...AND IS NEAR THE MODEL CONSENSUS.   

RECONNAISSANCE DATA THUS FAR DO NOT SUPPORT ANY INCREASE IN THE
INTENSITY ESTIMATE.  WATER VAPOR IMAGERY CONTINUES TO SHOW VERY DRY
AIR IMPINGING ON HANNA FROM THE SOUTHEAST...AND THIS IS EXPECTED TO
CONTINUE.  WHILE THE VERTICAL SHEAR IS FORECAST TO DIMINISH A
LITTLE PRIOR TO LANDFALL...NONE OF THE OBJECTIVE GUIDANCE MODELS
NOW MAKE HANNA A HURRICANE AND THE OFFICIAL INTENSITY FORECAST NOW
TOPS OUT AT 60 KT.  HURRICANE WATCHES WILL REMAIN IN EFFECT FOR THE
POSSIBILITY THAT HANNA BECOMES A LITTLE STRONGER THAN
FORECAST...AND PEOPLE ARE REMINDED THAT THERE IS VERY LITTLE
DIFFERENCE BETWEEN A STRONG TROPICAL STORM AND A MINIMAL HURRICANE.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      04/2100Z 25.5N  75.0W    55 KT
 12HR VT     05/0600Z 27.2N  76.4W    55 KT
 24HR VT     05/1800Z 30.3N  78.0W    60 KT
 36HR VT     06/0600Z 33.9N  78.3W    60 KT...ON THE COAST
 48HR VT     06/1800Z 37.5N  76.5W    50 KT...INLAND
 72HR VT     07/1800Z 46.0N  65.5W    40 KT...EXTRATROPICAL
 96HR VT     08/1800Z 51.0N  50.0W    40 KT...EXTRATROPICAL
120HR VT     09/1800Z 52.5N  32.5W    45 KT...EXTRATROPICAL
 
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FORECASTER FRANKLIN
 
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