Tropical Storm LISA

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TROPICAL STORM LISA DISCUSSION NUMBER   2
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL142010
500 AM EDT TUE SEP 21 2010

ENHANCED INFRARED AND SHORTWAVE IMAGERY...ALONG WITH AN AMSU
OVERPASS..INDICATE THAT THE TROPICAL CYCLONE HAS BECOME BETTER
ORGANIZED.  BURSTS OF DEEP CONVECTION ARE FORMING NEAR THE
CIRCULATION CENTER...AND CLOUD TOPS ASSOCIATED WITH A BANDING
FEATURE OVER THE EAST SEMICIRCLE HAVE COOLED TO -70 CELSIUS. 
DVORAK SATELLITE INTENSITY ESTIMATES ARE T2.5...35 KT...FROM BOTH
TAFB AND SAB.  THESE ESTIMATES ALONG WITH AN ADT ESTIMATE OF 39 KT
SUPPORT AN UPGRADE OF THE DEPRESSION TO A 35 KT TROPICAL STORM. 

THE SHEAR IS LOW...AND ENVIRONMENTAL CONDITIONS ARE EXPECTED TO
REMAIN CONDUCIVE FOR FURTHER STRENGTHENING DURING THE NEXT 36
HOURS.  THROUGH THE REMAINING PERIOD...THE LARGE-SCALE MODELS SHOW
AN UPPER ANTICYCLONE LOCATED OVER THE CENTRAL ATLANTIC OCEAN
RETROGRADING SOUTHWESTWARD TOWARD THE GREATER ANTILLES...AND A MID-
TO UPPER-LEVEL TROUGH TO THE NORTH OF LISA FILLING AND MOVING
NORTHEASTWARD.  THIS CHANGE IN THE SYNOPTIC PATTERN IS EXPECTED TO
INCREASE THE WESTERLY SHEAR ALONG THE FORECAST TRACK.  THE
INTENSITY FORECAST IS BASED ON THE AFOREMENTIONED SCENARIO AND IS A
COMPROMISE OF THE SHIPS MODEL AND THE LGEM.

THE INITIAL MOTION ESTIMATE IS 360/4...WITHIN THE WEAK STEERING
CURRENT ASSOCIATED WITH A BREAK IN THE SUBTROPICAL RIDGE OVER THE
EASTERN ATLANTIC.  THE GLOBAL MODELS...AS WELL AS THE ECMWF AND GFS
ENSEMBLES...SUGGEST A RATHER SLOW NORTHWARD MOTION DURING THE NEXT
36 HOURS.  BY DAY 2...A GRADUAL TURN TOWARD THE WEST-NORTHWEST IS
INDICATED AS THE TROUGH LIFTS NORTHEASTWARD AND THE SUBTROPICAL
RIDGE BUILDS IN TO THE NORTH OF THE CYCLONE.  THE NHC OFFICIAL
TRACK FORECAST REFLECTS A BLEND OF THE GLOBAL AND ENSEMBLE
MODELS...AND IS SHIFTED TO THE LEFT OF THE PREVIOUS ADVISORY.
 
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      21/0900Z 17.7N  31.8W    35 KT
 12HR VT     21/1800Z 18.0N  31.7W    45 KT
 24HR VT     22/0600Z 18.4N  31.7W    50 KT
 36HR VT     22/1800Z 18.7N  31.9W    55 KT
 48HR VT     23/0600Z 19.0N  32.6W    55 KT
 72HR VT     24/0600Z 19.8N  34.3W    55 KT
 96HR VT     25/0600Z 20.5N  35.5W    50 KT
120HR VT     26/0600Z 21.5N  37.0W    45 KT
 
$$
FORECASTER ROBERTS/BEVEN
 
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