513 
 WTNT44 KNHC 220841
 TCDAT4
 TROPICAL STORM LISA DISCUSSION NUMBER   6
 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   AL142010
 500 AM EDT WED SEP 22 2010
 
 INFRARED SATELLITE IMAGES INDICATE THAT THERE HAS BEEN LITTLE
 SIGNIFICANT CHANGE ASSOCIATED WITH THE CLOUD PATTERN OF LISA.  THE
 CYCLONE CONSISTS OF A CENTRAL MASS OF PULSATING DEEP CONVECTION...
 ALTHOUGH WITH FEWER BANDING FEATURES THAN YESTERDAY.  SEVERAL RECENT
 MICROWAVE OVERPASSES SUGGEST THAT THE LOW- AND MID-LEVEL CENTERS
 ARE NOT CO-LOCATED...A SIGN THAT THE CYCLONE IS BEING IMPACTED BY
 VERTICAL WIND SHEAR.  DVORAK CI NUMBERS AT 0600 UTC ARE AT 2.5 AND
 3.0 FROM SAB AND TAFB...RESPECTIVELY.  A BLEND OF THESE ESTIMATES
 IS THE BASIS FOR KEEPING THE INITIAL INTENSITY AT 40 KT FOR THIS
 ADVISORY.  
 
 THE CENTER HAS BEEN DIFFICULT TO LOCATE BUT RECENT MICROWAVE AND
 SATELLITE FIXES SUGGEST THAT IT BE A LITTLE FARTHER SOUTH THAN
 PREVIOUSLY INDICATED.  A SHORT-TERM INITIAL MOTION FROM THESE FIXES
 YIELDS AN ESTIMATE OF 060/4.  THE TRACK GUIDANCE CONTINUES TO BE
 FAIRLY DIVERGENT BUT GENERALLY SHOWS LISA DRIFTING SOUTH OR EAST IN
 A REGION OF WEAK STEERING DURING THE 48 HOURS.  AFTER THAT...A TURN
 TOWARD WEST-NORTHWEST IS EXPECTED WITH A FASTER FORWARD SPEED AS A
 WEAK LOW- TO MID-LEVEL RIDGE BUILDS NORTH OF THE STORM.  GIVEN THE
 LARGE SPREAD IN THE GLOBAL MODELS...THE NEW NHC TRACK FORECAST
 REMAINS OF LOW CONFIDENCE AND IS SLOWED FURTHER UNTIL A MORE
 ESTABLISHED TREND IS EVIDENT IN THE GUIDANCE.
 
 WATER VAPOR IMAGERY SHOWS A SHARP UPPER-LEVEL TROUGH NORTH OF LISA
 THAT IS FORECAST TO LIFT OUT IN 24-48 HOURS.  THIS FEATURE HAS BEEN
 IMPARTING A NORTHWESTERLY SHEAR OVER THE STORM...BUT SHIPS MODEL
 OUTPUT INDICATES THAT THIS SHEAR SHOULD NOT BE PARTICULARLY STRONG
 DURING THIS TIME.  AFTER ABOUT 60-72 HOURS...HOWEVER...GLOBAL
 MODELS FORECAST A STRENGTHENING OF UPPER-LEVEL WESTERLY FLOW OVER
 LISA...AND THE INTENSITY GUIDANCE SHOWS WEAKENING LATER IN THE
 PERIOD.  OF COURSE...THE INTENSITY GUIDANCE IS HIGHLY DEPENDENT ON
 WHERE LISA IS LOCATED AT THAT TIME...AND THE GREATER THAN NORMAL
 UNCERTAINTY REGARDING ITS FORECAST TRACK MAKES THE CURRENT
 INTENSITY FORECAST DIFFICULT.  THE NEW NHC INTENSITY FORECAST HAS
 BEEN ADJUSTED A BIT DOWNWARD BEFORE 72 HOURS BUT REMAINS AT OR
 ABOVE THE STATISTICAL-DYNAMICAL OUTPUT.
 
  
 FORECAST POSITIONS AND MAX WINDS
  
 INITIAL      22/0900Z 18.0N  30.5W    40 KT
  12HR VT     22/1800Z 18.0N  30.5W    45 KT
  24HR VT     23/0600Z 17.9N  30.5W    50 KT
  36HR VT     23/1800Z 17.8N  30.5W    50 KT
  48HR VT     24/0600Z 17.8N  30.7W    55 KT
  72HR VT     25/0600Z 18.5N  32.5W    50 KT
  96HR VT     26/0600Z 19.5N  35.0W    45 KT
 120HR VT     27/0600Z 21.0N  38.0W    35 KT
  
 $$
 FORECASTER KIMBERLAIN