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 356 
 WTNT44 KNHC 251443
 TCDAT4
 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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