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Tropical Storm PATTY (Text)

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TROPICAL STORM PATTY DISCUSSION NUMBER   3
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL162012
1100 PM EDT THU OCT 11 2012
 
CONVENTIONAL AND MICROWAVE SATELLITE IMAGERY INDICATE THAT THE TIGHT
LOW-LEVEL CIRCULATION CENTER IS DISPLACED TO THE SOUTHWEST OF THE
COLDEST CLOUD TOPS...JUST INSIDE THE SOUTHWESTERN EDGE OF THE
CONVECTIVE CLOUD CANOPY...DUE TO MODERATE SOUTHWESTERLY VERTICAL
WIND SHEAR. THIS SHEAR PATTERN HAS RESULTED IN CONSENSUS 00Z DVORAK
INTENSITY ESTIMATES OF T3.0/45 KT FROM TAFB AND SAB...AND AN ADT
ESTIMATE OF T2.9/43 KT. THEREFORE...THE INITIAL INTENSITY HAS BEEN
CONSERVATIVELY INCREASED TO 40 KT.

RECENT SSMIS...TRMM...AND WINDSAT MICROWAVE DATA INDICATE PATTY HAS
REMAINED ESSENTIALLY STATIONARY SINCE THE PREVIOUS ADVISORY. LITTLE
MOVEMENT...OR PERHAPS A SMALL CLOCKWISE LOOP...IS EXPECTED DURING
THE NEXT 24 HOURS AS THE CYCLONE REMAINS EMBEDDED IN NORTHEASTERLY
LOW-LEVEL FLOW AND BENEATH UPPER-LEVEL SOUTHWESTERLY FLOW. BY 36
HOURS AND BEYOND...THE GLOBAL AND REGIONAL MODELS ARE IN GENERAL
AGREEMENT ON THE LOW-/MID-LEVEL NORTHEASTERLY FLOW INCREASING AND
FORCING PATTY IN A SOUTHWESTWARD DIRECTION AS A LARGE HIGH PRESSURE
SYSTEM ALONG THE U.S. EAST COAST AMPLIFIES AND SHIFTS EASTWARD OVER
THE ATLANTIC. THE EXPECTED SOUTHWESTWARD MOTION WILL ALSO FORCE
PATTY INTO INCREASING VERTICAL WIND SHEAR...WHICH SHOULD CAUSE THE
SYSTEM TO WEAKEN AND BECOME VERTICALLY SHALLOW...AND DEGENERATE
INTO A REMNANT LOW OR TROUGH THAT GETS ADVECTED SOUTHWESTWARD OR
WESTWARD BY ENHANCED LOW-LEVEL EASTERLY FLOW. SINCE PATTY IS
EXPECTED TO PERSIST AS A TROPICAL CYCLONE LONGER THAN PREVIOUSLY
EXPECTED...ADDITONAL FORECAST POINTS HAVE BEEN ADDED. THE OFFICIAL
FORECAST TRACK CLOSELY FOLLOWS A BLEND OF THE GFS...GFS-ENSEMBLE...
AND FSU SUPERENSEMBLE FORECASTS...SINCE THOSE MODELS REFLECT A MORE
ROBUST TROPICAL CYCLONE THROUGH THE NEXT 36-48 HOURS.

A FORTUITOUS 11/2031 UTC DROPSONDE REPORT RECEIVED FROM AN AIR FORCE
RESERVE RECONNAISSANCE AIRCRAFT ENROUTE TO THE NORTHEASTERN
CARIBBEAN REGION INDICATED THE VERTICAL WIND SHEAR FROM 850-300 MB
WAS MUCH LESS THAN THE 28-30 KT 850-200 MB SHEAR ASSESSED BY THE
GFS-BASED SHIPS MODEL. THIS MIGHT EXPLAIN WHY PATTY HAS REMAINED
WELL-ORGANIZED TODAY DESPITE WHAT OTHERWISE APPEARS TO BE RATHER
HOSTILE SHEAR CONDITIONS. THE CURRENT SHEAR PATTERN IS EXPECTED TO
PERSIST FOR THE NEXT 24-36 HOURS AS AN UPPER-LEVEL LOW OVER THE
NORTHEASTERN CARIBBEAN SEA WEAKENS AND LIFTS OUT NORTHWARD AND TO
THE EAST OF PATTY...WHICH ACTS TO DECREASE THE UPPER-LEVEL WINDS
ACROSS THE CYCLONE. HOWEVER...BY 48 HOURS...SOUTHWESTERLY
UPPER-LEVEL WINDS ARE EXPECTED TO INCREASE SIGNIFICANTLY ACROSS THE
CYCLONE AS IT MOVES SOUTHWESTWARD...WHICH SHOULD ACT TO WEAKEN THE
SYSTEM AND CAUSE THE LOW- AND UPPER-LEVEL CIRCULATIONS TO DECOUPLE.
THE OFFICIAL INTENSITY FORECAST CLOSELY FOLLOWS A BLEND OF THE LGEM
AND FSU SUPERENSEMBLE INTENSITY GUIDANCE.

GIVEN THE STRONG SOUTHWESTERLY UPPER-LEVEL WINDS...IT IS UNLIKELY
THAT PATTY COULD REACH THE BAHAMAS AS A TROPICAL STORM...AND
THEREFORE NO WATCHES OR WARNINGS ARE IN EFFECT FOR THOSE ISLANDS.
 
FORECAST POSITIONS AND MAX WINDS
 
INIT  12/0300Z 25.9N  72.5W   40 KT  45 MPH
 12H  12/1200Z 25.8N  72.5W   40 KT  45 MPH
 24H  13/0000Z 25.7N  72.6W   40 KT  45 MPH
 36H  13/1200Z 25.5N  72.7W   35 KT  40 MPH
 48H  14/0000Z 25.0N  73.5W   30 KT  35 MPH
 72H  15/0000Z 24.0N  77.0W   25 KT  30 MPH...POST-TROP/REMNT LOW
 96H  16/0000Z 23.0N  81.0W   20 KT  25 MPH...POST-TROP/REMNT LOW
120H  17/0000Z...DISSIPATED
 
$$
FORECASTER STEWART
 
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