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| #377712 (Received by flhurricane at: 4:58 AM 21.Sep.2010) TCDAT4 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 |
