451 
 WTNT43 KNHC 201500
 TCDAT3
 TROPICAL STORM LISA DISCUSSION NUMBER   5
 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
 11 AM EDT MON SEP 20 2004
  
 LISA REMAINS A SMALLER THAN AVERAGE TROPICAL CYCLONE. BANDING
 FEATURES HAVE CONTINUED TO IMPROVE THIS MORNING...INCLUDING AND
 OCCASIONAL HINT OF A BANDING EYE FEATURE IN VISIBLE IMAGERY.
 MICROWAVE IMAGERY FROM 20/0903Z AMSU AND 20/0955Z SSMI OVERPASSES 
 REVEALED A SMALL MID-LEVEL EYE WAS PRESENT. SUCH FEATURES ARE
 TYPICALLY ASSOCIATED WITH 45-55 KT TROPICAL CYCLONES. THE INITIAL
 INTENSITY ESTIMATE WAS INCREASED TO 50 KT BASED ON RECENT UW-CIMSS
 AND CIRA AMSU PRESSURE ESTIMATES OF 999.1 AND 998 MB...
 RESPECTIVELY. THEREFORE...THE INITIAL INTENSITY HAS BEEN MADE
 HIGHER THAN THE DVORAK SATELLITE INTENSITY ESTIMATES OF 35 KT FROM
 BOTH TAFB AND SAB...AND 30 KT FROM AFWA.
  
 THE INITIAL MOTION ESTIMATE REMAINS 275/10.  THERE REMAINS NO
 SIGNIFICANT CHANGE TO THE PREVIOUS TRACK FORECAST OR REASONING.
 LISA IS EXPECTED TO MOVE IN A WEST TO WEST-NORTHWESTWARD MOTION
 THROUGHOUT THE FORECAST PERIOD AS THE SMALL CYCLONE MOVES AROUND
 THE PERIPHERY OF A NARROW SUBTROPICAL TO THE NORTH. THE RIDGE
 CURRENTLY BETWEEN LISA AND KARL TO THE NORTHWEST IS FORECAST BY
 MOST OF THE MODELS TO REMAIN INTACT TO SOME DEGREE. THE NOGAPS
 MODEL IS THE ONLY MODEL THAT WEAKENS THE RIDGE AND PULLS LISA
 NORTHWARD AFTER 72 HOURS. HOWEVER...NOGAPS IS THE ONLY MODEL THAT
 EVEN IDENTIFIES LISA BEYOND 24-36 HOURS...AND IT APPEARS TO BE
 SUFFERING FROM ITS USUAL OVERDEVELOPMENT OF THE CYCLONE...WHICH
 ALLOWS LISA TO ERODE THE NARROW RIDGE AND MOVE THROUGH IT. THIS
 SOLUTION HAS BEEN DISCOUNTED GIVEN THE CURRENT VERY SMALL DIAMETER
 OF LISA...AND THE STRONG HIGH PRESSURE SYSTEM TO THE NORTH EXPECTED
 TO KEEP THE DIAMETER OF THE CYCLONE SMALLER THAN AVERAGE THROUGHOUT
 THE FORECAST PERIOD. THE OFFICIAL FORECAST TRACK IS JUST AN UPDATE
 OF THE PREVIOUS TRACK AND IS CLOSE TO THE GFDL AND DEEP BAM MODELS. 
  
 SMALL COMPACT TROPICAL CYCLONES LIKE LISA ARE SUSCEPTIBLE TO SHARP
 CHANGES IN INTENSITY...BOTH STRENGTHENING AND WEAKENING. THE
 VERTICAL SHEAR IS FORECAST TO REMAIN AROUND 10 KT OR LESS FOR THE
 NEXT 24 HOURS...SO STRENGTHENING INTO A HURRICANE SEEMS
 LIKELY...PERHAPS EVEN BY LATER TODAY. BY 36 HOURS...LOW TO MODERATE
 NORTHEASTERLY VERTICAL SHEAR IS EXPECTED TO INHIBIT INTENSIFICATION
 ...SO ONLY SLOW STRENGTHENING IS FORECAST IN THE LONGER TIME
 PERIODS. IF LISA REMAINS SOUTH OF 15N LATITUDE WHERE THE SHEAR IS
 EXPECTED TO BE THE STRONGEST...THEN THE INTENSITY WILL LILELY BE
 LESS THAN WHAT IS CURRENTLY FORECAST AND INDICATED BY THE SHIPS
 INTENSITY MODEL.
  
 FORECASTER STEWART
  
 FORECAST POSITIONS AND MAX WINDS
  
 INITIAL      20/1500Z 13.6N  35.9W    50 KT
  12HR VT     21/0000Z 13.8N  37.3W    55 KT
  24HR VT     21/1200Z 14.3N  39.1W    65 KT
  36HR VT     22/0000Z 14.8N  40.6W    70 KT
  48HR VT     22/1200Z 15.5N  42.4W    75 KT
  72HR VT     23/1200Z 16.8N  45.5W    75 KT
  96HR VT     24/1200Z 17.0N  48.5W    75 KT
 120HR VT     25/1200Z 17.0N  51.5W    75 KT
  
  
 $$