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 374 
 WTPZ45 KNHC 280241
 TCDEP5
 TROPICAL STORM DARBY DISCUSSION NUMBER   6
 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
 8 PM PDT TUE JUL 27 2004
  
 DARBY APPEARS TO BE VERY CLOSE TO HURRICANE STRENGTH.  ALTHOUGH THE
 EARLIER BANDING EYE-LIKE FEATURE HAS DISAPPEARED...SUBJECTIVE
 CLASSIFICATIONS FROM TAFB AND SAB AT 0Z WERE BOTH T4.0...65 KT. 
 AFWA'S ESTIMATE WAS LOWER...AT 55 KT...AND THE MOST RECENT
 OBJECTIVE DVORAK NUMBERS FROM UW/CIMSS ARE ALSO BELOW HURRICANE
 STRENGTH.  CONSEQUENTLY DARBY IS BEING HELD AS A TROPICAL STORM FOR
 THIS ADVISORY.  ALTHOUGH DARBY WILL REMAIN IN A WARM WATER/LOW
 SHEAR ENVIRONMENT FOR THE NEXT 24-36 HOURS...NEITHER THE GFDL NOR
 THE SHIPS GUIDANCE IS CALLING FOR MORE THAN ABOUT 10 KT OF
 ADDITIONAL STRENGTHENING.  THE SHIPS GUIDANCE IN PARTICULAR IS
 SUGGESTING THAT THE THERMODYNAMIC ENVIRONMENT AHEAD OF DARBY WILL
 BE INCREASINGLY HOSTILE.  LATE IN THE FORECAST PERIOD...COOLER
 WATERS AND INCREASING WESTERLY SHEAR ARE EXPECTED TO WEAKEN
 THE CYCLONE.  THE OFFICIAL FORECAST IS VERY CLOSE TO THE SHIPS AND
 GFDL GUIDANCE.
 
 DARBY IS MOVING AT 290/13.  MODEL GUIDANCE IS IN PRETTY GOOD
 AGREEMENT ON A CONTINUATION OF THIS TRACK THROUGH 36 HOURS AS DARBY
 MOVES AROUND THE PERIPHERY OF THE SUBTROPICAL RIDGE.  IN A COUPLE
 OF DAYS...DARBY SHOULD BE SOUTH OF A WEAKNESS IN THE RIDGE THAT MAY
 CAUSE THE FORWARD SPEED TO SLOW...AND THIS IS REFLECTED IN THE
 OFFICIAL FORECAST.  AFTER THAT TIME...THE WEAKENING CYCLONE IS
 EXPECTED TO TURN TO A SLIGHTLY MORE WESTERLY TRACK.  THE GFS IS
 SOMETHING OF AN OUTLIER...CALLING FOR A RAPID WEAKENING OF DARBY
 FOLLOWED BY A RATHER QUICK TURN TO THE WEST.  THE OFFICIAL FORECAST
 IS DOWN THE MIDDLE OF THE GUIDANCE ENVELOPE AND IN BEST AGREEMENT
 WITH THE UKMET.
  
 FORECASTER FRANKLIN
  
 FORECAST POSITIONS AND MAX WINDS
  
 INITIAL      28/0300Z 14.4N 121.2W    60 KT
  12HR VT     28/1200Z 15.1N 122.9W    70 KT
  24HR VT     29/0000Z 15.7N 125.0W    75 KT
  36HR VT     29/1200Z 16.4N 127.1W    75 KT
  48HR VT     30/0000Z 17.0N 129.0W    70 KT
  72HR VT     31/0000Z 17.5N 133.0W    65 KT
  96HR VT     01/0000Z 18.0N 137.5W    55 KT
 120HR VT     02/0000Z 18.5N 142.0W    45 KT
  
  
 $$
 
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