546 
 WTPZ44 KNHC 100231
 TCDEP4
 TROPICAL STORM FLOSSIE DISCUSSION NUMBER   6
 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   EP092007
 800 PM PDT THU AUG 09 2007
  
 SATELLITE IMAGERY INDICATES THAT FLOSSIE HAS CHANGED LITTLE IN
 ORGANIZATION WITH OCCASIONAL GLIMPSES OF A FORMATIVE EYE AND AN
 EYEWALL FEATURE IN MICROWAVE IMAGERY.  DVORAK INTENSITY ESTIMATES
 FROM TAFB AND SAB REMAIN AT 55 KT...AND SO DOES THE OFFICIAL
 ADVISORY INTENSITY. IN THE SHORT-TERM...THE INTENSITY FORECAST HAS
 BECOME COMPLICATED BY THE DEVELOPMENT OF STRONG UPPER-LEVEL
 EASTERLY FLOW NOW APPROACHING FLOSSIE FROM THE EAST.  THE GLOBAL
 MODELS ARE UNDERESTIMATING THIS FLOW POSSIBLY LEADING TO AN
 OPTIMISTIC SHEAR FORECAST.  ARRESTED DEVELOPMENT COULD RESULT IF 
 THIS STRONG EASTERLY FLOW CATCHES THE CYCLONE...AND FLOSSIE COULD
 CURRENTLY BE AT OR VERY NEAR ITS PEAK INTENSITY.  TO MAINTAIN SOME
 CONTINUITY WITH THE PREVIOUS ADVISORY...THE INTENSITY FORECAST
 ALLOWS FOR SLIGHT STRENGTHENING DURING THE DIURNAL CONVECTIVE
 MAXIMUM LATER TONIGHT...AND THERE IS STILL A CHANCE FLOSSIE COULD
 BECOME A HURRICANE.  BY THE END OF THE FORECAST PERIOD...THE
 EUROPEAN AND UKMET MODELS SHOW THE DEVELOPMENT OF SIGNIFICANT
 WESTERLY SHEAR WHICH IS NOT SHOWN IN THE GFS.  ACCORDINGLY...THE
 OFFICIAL FORECAST IS BELOW THE GFS-BASED SHIPS MODEL. 
  
 THE PRIMARY STEERING MECHANISM CONTINUES TO BE A STRONG RIDGE
 EXTENDING WESTWARD FROM MEXICO RESULTING IN A MOTION JUST SOUTH OF
 DUE WEST OR 265/13.   FLOSSIE IS EXPECTED TO MAINTAIN A WESTWARD TO 
 WEST-NORTHWESTWARD TRACK THROUGH THE FORECAST PERIOD AS A NARROW
 RIDGE REMAINS NORTH OF THE CYCLONE.  MODEL GUIDANCE IS GENERALLY
 SPLIT INTO TWO CAMPS BASED ON THE EVENTUAL DEPTH AND STEERING OF
 THE CYCLONE. THE NOGAPS AND EUROPEAN MODELS...BOTH OF WHICH SHOW A
 WEAK VORTEX...LIE ON THE SOUTH SIDE OF THE MODEL SUITE.
 CONVERSELY...THE GFDL AND HWRF MODELS...WHICH SHOW FLOSSIE BECOMING
 A HURRICANE...LIE ON THE NORTH SIDE OF THE GUIDANCE ENVELOPE. 
 WHILE THE PRESENT TRENDS IN SATELLITE IMAGERY MAKE IT IS TEMPTING
 TO LEAN TOWARDS THE WEAKER NOGAPS/EUROPEAN SOLUTION...IT IS TOO
 SOON TO MAKE SUCH A SIGNIFICANT CHANGE TO THE TRACK FORECAST. 
 ACCORDINGLY...THE OFFICIAL FORECAST IS LARGELY UNCHANGED FROM THE
 PREVIOUS ADVISORY. 
  
 FORECAST POSITIONS AND MAX WINDS
  
 INITIAL      10/0300Z 12.6N 133.7W    55 KT
  12HR VT     10/1200Z 12.7N 135.6W    60 KT
  24HR VT     11/0000Z 13.0N 137.8W    60 KT
  36HR VT     11/1200Z 13.4N 139.8W    60 KT
  48HR VT     12/0000Z 13.8N 141.8W    55 KT
  72HR VT     13/0000Z 14.5N 146.0W    55 KT
  96HR VT     14/0000Z 15.5N 150.5W    50 KT
 120HR VT     15/0000Z 16.5N 155.0W    40 KT
  
 $$
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