Tropical Storm OPHELIA

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TROPICAL STORM OPHELIA DISCUSSION NUMBER  25
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL162011
500 PM AST WED SEP 28 2011
 
THE CLOUD PATTERN OF OPHELIA HAS NOT CHANGED MUCH SINCE THIS
MORNING...WITH A CURVED CONVECTIVE BAND PREVAILING AROUND THE
EASTERN AND NORTHERN PORTIONS OF THE CIRCULATION.  SINCE THERE HAS
BEEN LITTLE CHANGE IN APPEARANCE SINCE THE HURRICANE HUNTER MISSION
INTO THE STORM EARLIER TODAY...THE INITIAL WIND SPEED ESTIMATE
REMAINS AT 45 KT.   AN UPPER-LEVEL TROUGH LOCATED SEVERAL HUNDRED
MILES TO THE NORTHWEST OF OPHELIA IS PRODUCING WEST-SOUTHWESTERLY
VERTICAL SHEAR OVER THE STORM.  HOWEVER...THE SHEAR IS NOT EXPECTED
TO BE STRONG ENOUGH TO PREVENT SLOW STRENGTHENING.  IN 48 TO 72
HOURS...DYNAMICAL MODELS INDICATE SOME RELAXATION OF THE SHEAR AND
AROUND THIS TIME THE OFFICIAL FORECAST CALLS FOR OPHELIA TO BECOME
A HURRICANE.  THE OFFICIAL WIND SPEED FORECAST IS AGAIN CLOSE TO A
MULTI-MODEL CONSENSUS THAT INCLUDES THE NEW GUIDANCE FROM THE
HURRICANE FORECAST IMPROVEMENT PROJECT.  BY THE END OF THE FORECAST
PERIOD...GLOBAL MODELS SHOW THE SYSTEM EMBEDDED WITHIN A FRONT...
AND THEREFORE HAVING UNDERGONE EXTRATROPICAL TRANSITION.

THERE HAS BEEN SOME INCREASE IN FORWARD SPEED AND THE MOTION IS NOW
ABOUT 330/7.  THE TROPICAL CYCLONE IS EXPECTED TO MOVE ALONG THE
SOUTHWESTERN PERIPHERY OF A SUBTROPICAL HIGH PRESSURE AREA FOR THE
NEXT COUPLE OF DAYS.  BY AROUND 72 HOURS...THE FLOW BETWEEN THE
HIGH AND A LARGE MID-TROPOSPHERIC TROUGH MOVING OFF THE U.S. EAST
COAST SHOULD TURN OPHELIA NORTHWARD.  THE CYCLONE SHOULD ACCELERATE
NORTH-NORTHEASTWARD WITHIN THE FLOW ON THE EAST SIDE OF THE TROUGH
THEREAFTER.  THE OFFICIAL FORECAST IS A LITTLE FASTER AND A LITTLE
TO THE LEFT OF THE PREVIOUS ONE.  THIS IS BETWEEN THE MULTI-MODEL
CONSENSUS AND THE NEW GFS RUN...WHICH IS SIGNIFICANTLY FASTER THEN
THE 0600 UTC RUN.   

FORECAST POSITIONS AND MAX WINDS
 
INIT  28/2100Z 19.3N  60.6W   45 KT  50 MPH
 12H  29/0600Z 20.2N  61.0W   50 KT  60 MPH
 24H  29/1800Z 21.6N  61.7W   55 KT  65 MPH
 36H  30/0600Z 23.3N  62.5W   60 KT  70 MPH
 48H  30/1800Z 25.2N  63.2W   65 KT  75 MPH
 72H  01/1800Z 31.0N  62.5W   70 KT  80 MPH
 96H  02/1800Z 40.0N  59.0W   70 KT  80 MPH
120H  03/1800Z 52.0N  49.0W   50 KT  60 MPH...POST-TROP/EXTRATROP
 
$$
FORECASTER PASCH
 
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