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| #539740 (Received by flhurricane at: 4:47 AM 03.Sep.2012) TCDAT2 TROPICAL STORM LESLIE DISCUSSION NUMBER 16 NWS NATIONAL HURRICANE CENTER MIAMI FL AL122012 500 AM AST MON SEP 03 2012 A TREMENDOUS BURST OF DEEP CONVECTION CONTAINING CLOUD TOP TEMPERATURES OF -84C TO -88C HAS PERSISTED NEAR THE CENTER AND OVER THE SOUTHERN SEMICIRCLE FOR MORE THAN 6 HOURS. THE CLOUD CANOPY HAS GRADUALLY BEEN EXPANDING NORTHWARD...WHICH SUGGESTS THAT THE VERTICAL SHEAR IS NOT AS STRONG AS SOME OF THE MODELS HAVE BEEN INDICATING. RECENT MICROWAVE FIXES SUGGEST THAT THE LOW-LEVEL CIRCULATION CENTER IS LOCATED JUST INSIDE THE NORTHWESTERN PORTION OF THE MASSIVE CONVECTIVE CLOUD SHIELD. SATELLITE INTENSITY ESTIMATES USING A SHEAR PATTERN ARE T3.5/55 KT FROM TAFB AND T3.0/45 KT FROM SAB...PLUS AN ADT ESTIMATE T3.2/49 KT. GIVEN THE UNCERTAINTY IN THE EXACT LOCATION OF THE SURFACE CENTER...THE INTENSITY WILL REMAIN 50 KT FOR THIS ADVISORY. THE INITIAL MOTION ESTIMATE IS 335/07 KT. OTHER THAN A FEW WOBBLES HERE AND THERE...LESLIE HAS REMAINED BASICALLY ON TRACK. OVER THE NEXT 48 HOURS...THE LATEST MODEL GUIDANCE CONTINUES TO INDICATE THAT LESLIE WILL MOVE TOWARD A BREAK IN THE SUBTROPICAL RIDGE THAT IS BEING INDUCED BY A SHORTWAVE TROUGH LOCATED ALONG 65W. AS THE TROUGH CONTINUES TO MOVE EASTWARD...THE RIDGE WILL BUILD BACK IN TO THE NORTH OF THE CYCLONE AND CAUSE IT TO SLOW DOWN CONSIDERABLY ON DAYS 3 AND 4. HOWEVER...BY DAY 5...A SHORTWAVE TROUGH/UPPER-LOW CURRENTLY LOCATED OVER THE BAHAMAS IS FORECAST TO MOVE EASTWARD AND ACT TO LIFT LESLIE NORTHWARD OR NORTH-NORTHWESTWARD AT A FASTER FORWARD SPEED. THE OFFICIAL FORECAST IS IN THE MIDDLE OF THE FAIRLY TIGHT GUIDANCE ENVELOPE...AND LIES BETWEEN THE DYNAMICAL CONSENSUS MODELS TVCA AND TV15. THE GFS-BASED SHIPS MODEL IS CURRENTLY INDICATING MORE THAN 20 KT OF WEST-NORTHWESTERLY VERTICAL SHEAR ON THE CYCLONE...WHICH APPEARS TO BE OVERDONE DUE TO THE 500 KM RADIUS USED BY THAT MODEL TO COMPUTE SHEAR. THE LATEST UW-CIMSS SHEAR ANALYSIS INDICATES ONLY ABOUT 15 KT OF SHEAR...WHICH SEEMS MORE REASONABLE GIVEN THE TREMENDOUS AMOUNT OF DEEP CONVECTION THAT HAS PERSISTED SINCE THE PREVIOUS ADVISORY. THE SHIPS MODEL IS FORECASTING THE SHEAR TO INCREASE TO NEAR 30 KT FROM THE NORTHWEST OVER THE NEXT 24 HOURS. ALTHOUGH THESE SHEAR VALUES MAY BE SOMEWHAT OVERDONE...EVEN AN INCREASE IN TO AROUND 20 KT SHOULD BE ENOUGH TO HINDER THE INTENSIFICATION PROCESS FOR THE NEXT 24-36 HOURS. AFTER THAT...HOWEVER...THE SHEAR IS FORECAST TO GRADUALLY SUBSIDE AND ALL OF THE GLOBAL MODELS BUILD AN UPPER-LEVEL RIDGE OVER LESLIE AS THE CYCLONE MOVES BETWEEN THE UPPER-LEVEL LOW OVER THE BAHAMAS AND A DIGGING TROUGH ALONG 50W ON DAYS 4 AND 5. THIS FLOW PATTERN SHOULD CREATE CONDITIONS MORE CONDUCIVE FOR INTENSIFICATION. THE OFFICIAL INTENSITY FORECAST IS SIMILAR TO THE PREVIOUS ADVISORY...EXCEPT AT DAY 5 WHERE THE FORECAST IS HIGHER...BASED ON A BLEND OF THE SHIPS AND HWRF MODELS. FORECAST POSITIONS AND MAX WINDS INIT 03/0900Z 23.8N 62.1W 50 KT 60 MPH 12H 03/1800Z 24.7N 62.5W 50 KT 60 MPH 24H 04/0600Z 25.5N 62.8W 50 KT 60 MPH 36H 04/1800Z 26.1N 62.9W 50 KT 60 MPH 48H 05/0600Z 26.6N 62.9W 55 KT 65 MPH 72H 06/0600Z 27.6N 62.9W 60 KT 70 MPH 96H 07/0600Z 28.7N 63.3W 70 KT 80 MPH 120H 08/0600Z 30.8N 64.1W 80 KT 90 MPH $$ FORECASTER STEWART |
