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Tropical Storm LISA (Text)

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TROPICAL STORM LISA DISCUSSION NUMBER  20
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL142010
1100 AM AST SAT SEP 25 2010
 
ALTHOUGH OUTER BANDING FEATURES IN THE NORTHERN AND WESTERN
QUADRANTS HAVE ACTUALLY IMPROVED SINCE THE LAST ADVISORY...
SATELLITE IMAGERY INDICATES THE CENTRAL DEEP CONVECTION HAS ERODED
SOME DUE TO MODERATE WESTERLY SHEAR IMPINGING ON LISA. THE INITIAL
INTENSITY OF 60 KT IS BASED ON A BLEND OF SATELLITE INTENSITY
ESTIMATES T4.5/77 KT FROM TAFB... T2.4/35 KT FROM SAB...AND AN ADT
VALUE OF T3.8/61 KT FROM UW-CIMSS....AND THE CYCLONE HAS BEEN
DOWNGRADED TO TROPICAL STORM STATUS AGAIN.

LISA IS ON THE PREVIOUS FORECAST TRACK AND THE INITIAL MOTION
ESTIMATE IS NOW 350/10. THROUGHOUT THE FORECAST PERIOD...LISA IS
EXPECTED TO MOVE NORTH TO NORTH-NORTHWESTWARD AROUND THE WESTERN
PERIPHERY OF THE BROAD SUBTROPICAL RIDGE SITUATED OVER NORTHWESTERN
AFRICA. ALL OF THE GLOBAL AND REGIONAL MODELS ARE IN MUCH BETTER
AGREEMENT ON THIS SCENARIO THAN IN PREVIOUS MODEL RUNS...ASSUMING
THAT LISA MAINTAINS VERTICAL COHERENCE THROUGH AT LEAST 72 HOURS.
THE OFFICIAL FORECAST TRACK IS SIMILAR TO THE PREVIOUS ADVISORY AND
IS CLOSE TO THE CONSENSUS MODEL...TVCN.

WESTERLY TO SOUTHWESTERLY VERTICAL SHEAR IS FORECAST TO INCREASE TO
ABOVE 25 KT BY 24 HOURS AND CONTINUE INCREASE TO NEAR 35 KT BY
36-48 HOURS. THIS UNFAVORABLE UPPER-LEVEL FLOW PATTERN SHOULD
CONTINUE THE CURRENT WEAKENING TREND. ALTHOUGH LISA IS PRESENTLY
LOCATED OVER RELATIVELY COOL SSTS OF 25.5C...THE CYCLONE IS NOT
FORECAST TO MOVE OVER WATER ANY COOLER THAN THOSE CURRENT OCEAN
TEMPERATURES. HOWEVER...THE GFS-BASED SHIPS MODEL INDICATES THAT
UPPER-LEVEL TEMPERATURES ARE FORECAST TO COOL BY AT LEAST 3 DEGREES
CELSIUS...WHICH WOULD RESULT IN GREATER INSTABILITY AHEAD OF LISA
THAN WHAT THE CYCLONE IS CURRENTLY INGESTING. THE RESULT IS THAT
DEEP CONVECTION COULD PERSIST NEAR THE CENTER...ALBEIT SHEARED TO
THE EAST...AND PREVENT LISA FROM BECOMING A NON-CONVECTIVE REMNANT
LOW PRESSURE SYSTEM AS EARLY AS INDICATED BY THE OFFICIAL FORECAST.

 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      25/1500Z 22.7N  28.2W    60 KT
 12HR VT     26/0000Z 23.9N  28.4W    50 KT
 24HR VT     26/1200Z 25.3N  28.6W    45 KT
 36HR VT     27/0000Z 26.6N  28.8W    40 KT
 48HR VT     27/1200Z 27.9N  29.1W    35 KT
 72HR VT     28/1200Z 30.1N  29.6W    30 KT...POST-TROP/REMNT LOW
 96HR VT     29/1200Z 32.0N  30.0W    25 KT...POST-TROP/REMNT LOW
120HR VT     30/1200Z...DISSIPATED
 
$$
FORECASTER STEWART
 
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