371 
 WTPZ45 KNHC 270842
 TCDEP5
 TROPICAL STORM DARBY DISCUSSION NUMBER   3
 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
 2 AM PDT TUE JUL 27 2004
  
 TROPICAL STORM DARBY HAS BECOME MUCH BETTER ORGANIZED DURING THE
 PAST 6 HOURS AND HAS DEVELOPED A CENTRAL DENSE OVERCAST...OR CDO...
 FEATURE. THE LOW-LEVEL CENTER APPEARS TO BE EMBEDDED IN THE MIDDLE
 OF THE CDO AND UPPER-LEVEL OUTFLOW HAS ALSO IMPROVED AND BECOME
 MORE CIRCULAR. THE INITIAL INTENSITY OF 45 KT IS BASED ON A BLEND
 OF DVORAK SATELLITE INTENSITY ESTIMATES OF 55 KT...45 KT...AND 30
 KT FROM SAB...TAFB...AND AFWA...RESPECTIVELY.
  
 THE INITIAL MOTION ESTIMATE REMAINS 280/12. THE OVERALL CONVECTIVE
 CLOUD PATTERN HAS BEEN TRANSLATING A LITTLE NORTH OF DUE WEST THE
 PAST 24 HOURS. IRONICALLY...THE DYNAMICAL MODELS HAVE ALL TAKEN
 DARBY OFF TO THE NORTHWEST FROM ITS INITIAL POSITIONS DURING THE
 SAME TIME FRAME. THE GFS...NOGAPS...AND THE GFDL MODELS HAVE BEEN
 THE WORSE AND HAVE HAD A 30 DEGREE RIGHT-OF-TRACK BIAS OVER THE
 LAST FEW MODEL RUNS. THE UKMET HAS HAD ONLY A SLIGHTLY LESS RIGHT
 BIAS. THIS APPEARS TO BE DUE TO THE GLOBAL MODELS HAVING POORLY
 INITIALIZED AN ALLEGED WEAKNESS IN THE SUBTROPICAL RIDGE TO THE
 NORTH OF DARBY. WATER VAPOR IMAGERY AND THE LATEST UW-CIMSS WATER
 VAPOR WIND ANALYSES INDICATE THE MID- TO UPPER-LEVEL FLOW NORTHWEST
 THROUGH NORTHEAST OF DARBY IS WESTERLY AT 10-15 KT. IN ADDITION...
 WATER VAPOR IMAGERY INDICATES THE UPPER-LEVEL LOW THAT HAD BEEN
 LOCATED ABOUT 500 NMI NORTH-NORTHWEST OF THE DARBY HAS BEEN MOVING
 RAPIDLY NORTHWESTWARD AWAY FROM THE CYCLONE...WHICH HAS LIKELY
 RESULTED IN THE ELIMINATION OF THE WEAKNESS IN THE SUBTROPICAL
 RIDGE. AS A RESULT...THE OFFICIAL FORECAST TRACK IS A LITTLE SOUTH
 OF THE PREVIOUS FORECAST TRACK AND IS CLOSE TO A BLEND OF THE
 STATISTICAL-DYNAMICAL MODEL...P91E...AND THE MEDIUM AND DEEP BAM.
 
 SATELLITE IMAGERY INDICATES THAT DARBY IS REALLY STARTING TO WIND UP
 A TIGHT CONVECTIVE BAND...SO A PERIOD OF RAPID INTENSIFICATION IS
 FORECAST FOR THE NEXT 24 HOURS OR SO. THIS IS SUPPORTED BY DARBY 
 FORECAST TO REMAIN IN A VERY FAVORABLE UPPER-LEVEL FLOW REGIME WITH
 VERTICAL SHEAR GRADUALLY DECREASING TO LESS THAN 5 KT BY 36 HOURS.
 THE ONLY HINDERING INFLUENCE APPEARS TO BE THE COOLER WATER THAT
 DARBY WILL BE PASSING OVER AFTER 72 HOURS...AND THIS IS REFLECTED
 BY A WEAKENING FORECAST AT 96 AND 120 HOURS. HOWEVER...IF AN EYE
 DEVELOPS DURING THE NEXT 6-12 HOURS...THEN RAPID STRENGTHENING
 COULD LAST LONGER THAN CURRENTLY FORECAST AND DARBY COULD BECOME A
 MAJOR HURRICANE BY 36-48 HOURS WHILE STILL OVER 27-28C SSTS.
  
 FORECASTER STEWART
  
 FORECAST POSITIONS AND MAX WINDS
  
 INITIAL      27/0900Z 12.8N 117.3W    45 KT
  12HR VT     27/1800Z 13.2N 118.9W    60 KT
  24HR VT     28/0600Z 13.8N 120.9W    70 KT
  36HR VT     28/1800Z 14.3N 122.8W    80 KT
  48HR VT     29/0600Z 14.8N 124.9W    85 KT
  72HR VT     30/0600Z 15.5N 128.7W    85 KT
  96HR VT     31/0600Z 16.0N 132.5W    80 KT
 120HR VT     01/0600Z 16.5N 137.0W    75 KT
  
  
 $$