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| #378615 (Received by flhurricane at: 4:38 AM 25.Sep.2010) TCDAT4 HURRICANE LISA DISCUSSION NUMBER 19 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL142010 500 AM AST SAT SEP 25 2010 INFRARED SATELLITE IMAGES INDICATE THAT LISA HAS MAINTAINED A CENTRAL MASS OF COLD-TOPPED CONVECTION DURING THE LAST SEVERAL HOURS. HOWEVER...THE CONVECTIVE STRUCTURE ASSOCIATED WITH THE HURRICANE IS LESS SYMMETRIC THAN IT WAS EARLIER...AND THE OUTFLOW HAS BECOME RESTRICTED TO THE WEST. AN 0347 UTC AMSU-B PASS ALSO INDICATED THAT THE LOW- AND MID-LEVEL WERE BEGINNING TO DECOUPLE. DVORAK T-NUMBERS WERE 3.5 AND 4.5 AT 0600 UTC FROM SAB AND TAFB... RESPECTIVELY...AND A BLEND OF THESE VALUES IS THE BASIS FOR AN INITIAL INTENSITY OF 65 KT. THE RECENT DEGRADATION OF THE CLOUD PATTERN SUGGESTS THAT UPPER-LEVEL SOUTHWESTERLY FLOW IS IN THE PROCESS OF INCREASING...AND UW-CIMSS ANALYSES SHOW CLOSE TO 20 KT OF SHEAR. AS THE CYCLONE GAINS LATITUDE IN THE NEXT DAY OR TWO...IT SHOULD ENCOUNTER A FURTHER INCREASE IN THE SHEAR AS WELL AS A DRIER/MORE STABLE AIR MASS AND A COOLER OCEAN SURFACE. THESE FACTORS SHOULD CONTRIBUTE TO WEAKENING WHICH COULD POTENTIALLY OCCUR AT A RAPID PACE. THE NEW NHC INTENSITY FORECAST IS REDUCED FROM THE PREVIOUS ONE NOW THAT LISA HAS PEAKED AND IS CLOSEST TO THE DYNAMICAL GUIDANCE. LISA APPEARS TO BE MOVING JUST WEST OF DUE NORTH...AND THE INITIAL MOTION ESTIMATE IS 355/08. GLOBAL MODELS SHOW THE CYCLONE SANDWICHED BETWEEN MID-LEVEL HIGH PRESSURE OVER NORTHWEST AFRICA AND A MID- TO UPPER-LEVEL TROUGH ALONG 35W. THIS SYNOPTIC PATTERN SHOULD STEER LISA ON A GENERAL NORTHWARD TRACK DURING THE NEXT SEVERAL DAYS SO LONG AS IT MAINTAINS VERTICAL INTEGRITY. AN ALTERNATE SCENARIO IS FOR A WEAKER LISA...HAVING BECOME A MORE SHALLOW SYSTEM SOONER THAN FORECAST...TO SLOW AND THEN TURN SOUTHWESTWARD IN THE LOW-LEVEL TRADES AS DEPICTED IN THE UKMET. THE OFFICIAL NHC TRACK FORECAST IS VERY NEAR THE PREVIOUS ONE... IMMEDIATELY LEFT OF THE MULTI-MODEL CONSENSUS. FORECAST POSITIONS AND MAX WINDS INITIAL 25/0900Z 21.6N 28.1W 65 KT 12HR VT 25/1800Z 23.1N 28.3W 60 KT 24HR VT 26/0600Z 24.7N 28.5W 55 KT 36HR VT 26/1800Z 26.1N 28.6W 50 KT 48HR VT 27/0600Z 27.4N 28.7W 45 KT 72HR VT 28/0600Z 29.5N 29.0W 30 KT...POST-TROP/REMNT LOW 96HR VT 29/0600Z 31.6N 29.5W 25 KT...POST-TROP/REMNT LOW 120HR VT 30/0600Z...DISSIPATED $$ FORECASTER KIMBERLAIN |
