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| #378502 (Received by flhurricane at: 4:50 PM 24.Sep.2010) TCDAT4 TROPICAL STORM LISA DISCUSSION NUMBER 16 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL AL142010 500 PM AST FRI SEP 24 2010 CONVENTIONAL AND MICROWAVE SATELLITE IMAGERY INDICATES LISA HAS CONTINUED TO BECOME BETTER ORGANIZED AND HAS STRENGTHENED. A RECENT TRMM OVERPASS REVEALED A CLOSED LOW-LEVEL EYE WITH A DIAMETER OF ABOUT 8-10 NMI...AND VISIBLE AND INFRARED IMAGERY HAVE BEEN HINTING THAT AN EYE HAS ALSO BEEN TRYING TO FORM. THE INITIAL INTENSITY OF 50 KT IS BASED ON A BLEND OF SATELLITE ESTIMATES OF T3.0/45 KT FROM BOTH TAFB AND SAB...TAFB AODT ESTIMATES OF T3.4/53 KT...AND UW-CIMSS 3-HR AVERAGE ADT ESTIMATES OF T3.4/53 KT. GIVEN THE VERY SMALL SIZE OF THE INNER-CORE CIRCULATION...WHICH RESTRICTS THE VARIOUS SATELLITE INTENSITY TECHNIQUES...IT IS POSSIBLE THAT LISA COULD BE STRONGER THAN INDICATED IN THIS ADVISORY. THE INITIAL MOTION ESTIMATE IS 360/07. FOR THE NEXT 24-36 HOURS... LISA IS FORECAST TO MOVE NORTHWARD AROUND THE WESTERN PERIPHERY OF THE LARGE SAHARAN SUBTROPICAL RIDGE LOCATED TO THE EAST OF THE CYCLONE. BY 48 HOURS...LISA IS EXPECTED TO MOVE INTO AN ENVIRONMENT OF STRONG SOUTHWESTERLY SHEAR FORECAST TO DEVELOP AHEAD OF A SHORTWAVE TROUGH CURRENTLY DIGGING SOUTHEASTWARD OVER THE CENTRAL ATLANTIC. THE EXPECTED RESULT IS THAT THE LOW-LEVEL AND UPPER-LEVEL CIRCULATIONS WILL DECOUPLE IN 72-96 HOURS...WITH THE LOW-LEVEL CIRCULATION MOVING NORTH-NORTHWESTWARD OR EVEN NORTHWESTWARD AS A REMNANT LOW PRESSURE SYSTEM THAT WILL BE STEERED BY THE LARGE SURFACE BERMUDA HIGH LOCATED OVER THE CENTRAL ATLANTIC. IN CONTRAST...THE GFDL AND HWRF MODELS MOVE LISA NORTHEASTWARD AFTER 72 HOURS AS A SIGNIFICANT TROPICAL CYCLONE. THOSE SCENARIOS ARE BEING DISCOUNTED AT THIS TIME DUE TO THEIR KNOWN BIAS IN RESISTING STRONG VERTICAL SHEAR CONDITIONS. THE OFFICIAL FORECAST TRACK IS A LITTLE TO THE RIGHT OF THE PREVIOUS ADVISORY...AND IS CLOSE TO THE NHC CONSENSUS MODEL...TVCN. SATELLITE IMAGERY SHOWS MODERATE CONVECTION OCCURRING AT LEAST 200 NMI TO THE NORTH OF LISA. THIS INDICATES THAT THERE IS AVAILABLE INSTABILITY FOR THE CYCLONE TO TAP IN TO DESPITE THE SUB-26C SSTS THAT LIE AHEAD OF THE SYSTEM. AS A RESULT...SOME ADDITIONAL STRENGTHENING IS EXPECTED DURING THE NEXT 12-24 HOURS...AND IT IS POSSIBLE THAT LISA COULD BECOME A HURRICANE. HOWEVER...BY 36 HOURS LISA IS FORECAST TO ENCOUNTER STRONG SHEAR OF MORE THAN 30 KT... WHICH SHOULD INDUCE STEADY WEAKENING. LISA IS FORECAST TO DEGENERATE INTO A REMNANT LOW PRESSURE SYSTEM BY 96 HOURS AND DISSIPATE BY 120 HOURS. THE OFFICIAL INTENSITY FORECAST IS SIMILAR TO A BLEND OF THE SHIPS AND LGEM INTENSITY MODELS AT ALL TIMES. FORECAST POSITIONS AND MAX WINDS INITIAL 24/2100Z 20.0N 27.8W 50 KT 12HR VT 25/0600Z 21.0N 28.0W 55 KT 24HR VT 25/1800Z 22.5N 28.3W 50 KT 36HR VT 26/0600Z 24.1N 28.7W 45 KT 48HR VT 26/1800Z 25.3N 29.1W 35 KT 72HR VT 27/1800Z 27.3N 29.9W 30 KT 96HR VT 28/1800Z 29.0N 30.5W 25 KT...POST-TROP/REMNT LOW 120HR VT 29/1800Z...DISSIPATED $$ FORECASTER STEWART |
