Tropical Storm LESLIE

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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
 
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