589 
 WTPZ45 KNHC 280836
 TCDEP5
 HURRICANE DARBY DISCUSSION NUMBER   7
 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL
 2 AM PDT WED JUL 28 2004
  
 SSMI MICROWAVE DATA AT 28/0336Z AND 28/0507Z CLEARLY INDICATE THAT
 DARBY HAS DEVELOPED A 20-25 NMI DIAMETER EYE...WHICH MAKES CENTER
 PLACEMENT FAIRLY STRAIGHTFORWARD. HOWEVER...THE INTENSITY ESTIMATE
 IS SOMEWHAT PROBLEMATIC GIVEN THE LARGE VARIANCE IN THE SATELLITE
 INTENSITY ESTIMATES...WHICH RANGE FROM 77 KT FROM TAFB TO 65 KT
 FROM SAB...AND 55 KT FROM AFWA. IN ADDITION...AUTOMATED ODT VALUES
 FROM UW-CIMSS ARE AROUND 69 KT WITH A COUPLE OF RAW VALUES OF 77
 KT. BASED ON A BLEND OF THE ODT VALUES...A ROUND CDO FEATURE...AND
 THE WELL-DEFINED EYE NOTED IN THE MICROWAVE IMAGES...THE INITIAL
 INTENSITY IS INCREASED TO 70 KT AND DARBY IS UPGRADED TO THE SECOND
 HURRICANE OF THE 2004 EASTERN NORTH PACIFIC HURRICANE SEASON. 
  
 THE INITIAL MOTION IS 290/12. THE LATEST NHC MODEL GUIDANCE IS IN
 MUCH BETTER AGREEMENT ON DARBY MAINTAINING A WEST-NORTHWESTWARD
 MOTION FOR THE NEXT 36-48 HOURS ACCOMPANIED BY A GRADUAL DECREASE
 IN FORWARD SPEED. BY 72 HOURS...A MORE WESTWARD TURN IS EXPECTED
 AFTER THE CYCLONE MOVES OVER COOLER WATER AND THE DOMINANT STEERING
 FLOW IS THE STRENGTHENING LOW-LEVEL RIDGE TO THE NORTH. SINCE THE
 LATEST SATELLITE FIXES HAVE BEEN BASICALLY COMING IN ON TRACK...THE
 OFFICIAL TRACK IS JUST AN UPDATE OF THE PREVIOUS FORECAST TRACK AND
 IS IN CLOSE AGREEMENT WITH THE GUNA MODEL CONSENSUS.
 
 NOW THAT DARBY HAS DEVELOPED A WELL-DEFINED EYE...SOME ADDITIONAL
 SIGNIFICANT STRENGTHENING IS STILL POSSIBLE BEFORE THE HURRICANE
 MOVES OVER SUB-26C SSTS IN 36-48 HOURS SINCE DARBY REMAINS IN A LOW
 SHEAR ENVIRONMENT AND OVER 27.5 SSTS. ALTHOUGH THE CYCLONE HAS BEEN
 RAPIDLY INTENSIFYING FOR THE PAST 30 HOURS...SUCH PHASES RARELY
 EXCEED 36 HOURS. AS SUCH... THE CURRENT INTENSITY TREND IS BEING
 LEVELED OFF SOMEWHAT. THIS IS CONSISTENT WITH THE SHIPS INTENSITY
 MODEL.
  
 FORECASTER STEWART
  
 FORECAST POSITIONS AND MAX WINDS
  
 INITIAL      28/0900Z 14.8N 122.3W    70 KT
  12HR VT     28/1800Z 15.4N 123.9W    75 KT
  24HR VT     29/0600Z 16.0N 125.9W    80 KT
  36HR VT     29/1800Z 16.5N 127.8W    80 KT
  48HR VT     30/0600Z 17.0N 130.0W    70 KT
  72HR VT     31/0600Z 17.6N 134.3W    60 KT
  96HR VT     01/0600Z 18.0N 139.0W    50 KT
 120HR VT     02/0600Z 18.5N 143.0W    40 KT
  
  
 $$