000
WTNT42 KNHC 020858
TCDAT2
 
TROPICAL STORM LESLIE DISCUSSION NUMBER  12
NWS NATIONAL HURRICANE CENTER MIAMI FL       AL122012
500 AM AST SUN SEP 02 2012
 
THE CENTER OF LESLIE REMAINS SHEARED TO THE NORTHWEST OF THE MAIN
CONVECTIVE CLOUD MASS. HOWEVER...CONVECTION HAS GRADUALLY BEEN
DEVELOPING CLOSER TO THE CENTER OVER THE PAST 6 HOURS...AND DVORAK
INTENSITY ESTIMATES FROM TAFB HAVE BEEN VARYING BETWEEN T3.0/45 KT
AND T3.5/55 KT. A 02/0134 UTC ASCAT OVERPASS INDICATED A PEAK WIND
VECTOR OF 51 KT SURROUNDED BY SEVERAL 50-KT VECTORS. ADJUSTING FOR
THE KNOWN LOW BIAS OF ASCAT WINDS YIELDS SURFACE WIND SPEEDS OF
NEAR 60 KT...AND THAT IS THE INTENSITY USED FOR THIS ADVISORY.

LESLIE IS MOVING NORTHWESTWARD...OR 310/13 KT. THE NHC MODEL
GUIDANCE REMAINS IN GOOD AGREEMENT ON LESLIE GRADUALLY TURNING
NORTHWARD AND ACCOMPANIED BY A DECREASE IN FORWARD SPEED DURING THE
NEXT 48 HOURS AS THE CYCLONE MOVES INTO A BREAK IN THE SUBTROPICAL
RIDGE BETWEEN 60-65W LONGITUDE. BY 72 HOURS...HOWEVER...THE BROAD
TROUGH/UPPER LOW CREATING THE BREAK IN THE RIDGE IS FORECAST TO
LIFT OUT TO THE NORTHEAST...WHICH WILL ALLOW A TRAILING SHORTWAVE
RIDGE TO BUILD IN TO THE NORTH OF LESLIE ON DAYS 4 AND 5. THIS
SHOULD RESULT IN A BLOCKING FLOW PATTERN DEVELOPING AROUND THE
CYCLONE THAT WILL CAUSE LESLIE TO SLOW DOWN TO LESS THAN 5 KT...AND
POSSIBLY EVEN BECOME STATIONARY DURING THE LATTER FORECAST PERIODS.
THE OFFICIAL FORECAST TRACK IS AN UPDATE OF THE PREVIOUS
TRACK...AND IS SIMILAR TO THE CONSENSUS MODELS TVCA AND TV15.
 
THE VERTICAL WIND SHEAR AFFECTING LESLIE IS EXPECTED TO BE MODERATE
FOR THE NEXT 24 HOURS OR SO...WHICH SHOULD CAP ANY SIGNIFICANT
INTENSIFICATION. AT 36 AND 48 HOURS...THE SHEAR IS FORECAST TO
INCREASE TO NEAR 30 KT...WHICH IS EXPECTED TO CAUSE THE CYCLONE TO
WEAKEN SOME. ASSUMING LESLIE SURVIVES THE DAY 2 HOSTILE SHEAR
CONDITIONS...THE UPPER-LEVEL WIND ENVIRONMENT IS FORECAST TO
IMPROVE AND BECOME CONDUCIVE FOR SIGNIFICANT STRENGTHENING TO
OCCUR. THE INTENSITY FORECAST REMAINS ON THE CONSERVATIVE SIDE AT
DAYS 4 AND 5 DUE TO THE UNCERTAINTY IN JUST HOW MUCH LESLIE WILL
WEAKEN OVER THE DAY 2-3 TIME PERIOD. THE OFFICIAL INTENSITY
FORECAST IS SIMILAR TO THE PREVIOUS ADVISORY...AND REMAINS ALONG
THE LOWER END OF THE GUIDANCE ENVELOPE NEAR THE SHIPS-LGEM
CONSENSUS.

THE INITIAL 34-KT AND 50-KT WIND RADII WERE INCREASED BASED ON WIND
DATA FROM THE AFOREMENTIONED ASCAT OVERPASS...WHICH CAPTURED THE
ENTIRE CIRCULATION OF LESLIE.

FORECAST POSITIONS AND MAX WINDS
 
INIT  02/0900Z 20.8N  59.5W   60 KT  70 MPH
 12H  02/1800Z 22.0N  60.9W   60 KT  70 MPH
 24H  03/0600Z 23.7N  62.1W   60 KT  70 MPH
 36H  03/1800Z 25.0N  62.6W   55 KT  65 MPH
 48H  04/0600Z 25.9N  62.7W   55 KT  65 MPH
 72H  05/0600Z 26.9N  62.4W   55 KT  65 MPH
 96H  06/0600Z 28.0N  62.5W   65 KT  75 MPH
120H  07/0600Z 29.2N  63.0W   70 KT  80 MPH
 
$$
FORECASTER STEWART