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Tropical Storm LISA (Text)

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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
 
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FORECASTER STEWART
 
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