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| #549433 (Received by flhurricane at: 10:59 PM 11.Oct.2012) TCDAT1 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 |
