Tropical Storm DARBY

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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
 
 
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