Hurricane DARBY

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HURRICANE DARBY DISCUSSION NUMBER  13
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   EP052010
800 PM PDT FRI JUN 25 2010
 
EVEN THOUGH DARBY HAS MAINTAINED A SMALL CENTRAL DENSE OVERCAST
DURING THE LAST SEVERAL HOURS...THE EYE TEMPERATURE HAS COOLED
AS THE EYE HAS BECOME MORE RAGGED.  IN ADDITION...THE CLOUD
PATTERN HAS BECOME LESS SYMMETRIC...WITH RECENT SATELLITE IMAGES
INDICATING A SOMEWHAT ELONGATED APPEARANCE TO THE CONVECTIVE TOPS. 
DVORAK SATELLITE CLASSIFICATIONS FROM TAFB AND SAB ARE 5.0/90KT AND
5.5/102 KT...RESPECTIVELY...WHILE ADVANCED OBJECTIVE DVORAK
ESTIMATES PEAKING EARLIER AROUND 5.5 HAVE BEGUN TO DECREASE.  ON
THE BASIS OF RECENT TRENDS AND SLIGHTLY LOWER DVORAK INTENSITY
ESTIMATES...THE INITIAL INTENSITY IS LOWERED TO 100 KT.  THE GLOBAL
MODELS CONTINUE TO INDICATE AN ABRUPT INCREASE IN EASTERLY VERTICAL
WIND SHEAR OVER DARBY WITHIN THE NEXT 6-12 HOURS...WITH THE SHEAR
POSSIBLY BECOMING RATHER STRONG AFTER 48 HOURS.  THE OFFICIAL
INTENSITY FORECAST IS ADJUSTED DOWNWARD FROM THE PREVIOUS
ADVISORY...AND CLOSELY FOLLOWS THE SHIPS/LGEM INTENSITY GUIDANCE. 
HOWEVER...DARBY COULD WEAKEN FASTER THAN FORECAST IF PERSISTENTLY
STRONG EASTERLY SHEAR DEVELOPS AND THE CURRENT INTENSITY FORECAST
IS OF LOW CONFIDENCE.
 
CENTER FIXES ARE A BIT TO THE RIGHT OF PREVIOUS ONES AND YIELD AN
INITIAL MOTION ESTIMATE OF 290/5. HOWEVER...RECENT SATELLITE
IMAGERY INDICATES THAT THE FORECAST TURN TOWARD THE WEST MAY
ALREADY BE OCCURRING. WATER VAPOR IMAGERY SHOWS DARBY ON THE
WESTERN EDGE OF MID- TO UPPER-TROPOSPHERIC RIDGING EXTENDING FROM
THE WESTERN CARIBBEAN THROUGH SOUTHERN MEXICO.  MODEL GUIDANCE
INDICATES THAT THIS RIDGING WILL WEAKEN DURING THE NEXT 24 HOURS...
LEAVING DARBY IN A REGION OF WEAK ENVIRONMENTAL STEERING. 
THEREAFTER...MODEL SOLUTIONS DIVERGE CONSIDERABLY...WITH ONE CAMP
OF MODELS NEARLY STALLING DARBY BEFORE MOVING IT ON A SLOW WESTWARD
TO NORTHWESTWARD COURSE.  THE OTHER SET OF SOLUTIONS SHOWS THE
SMALL CYCLONE BEING DRAWN EASTWARD BY THE LARGE CIRCULATION
ASSOCIATED WITH TROPICAL DEPRESSION ONE  ENTERING THE SOUTHERN GULF
OF MEXICO. THE NEW FORECAST TRACK IS ADJUSTED SLIGHTLY TO THE LEFT
AFTER 72 HOURS TO ACCOUNT FOR A SLIGHT WESTWARD SHIFT IN THE
GUIDANCE BUT NOT AS FAR WEST AS THE MULTI-MODEL CONSENSUS. GIVEN
THE DISAGREEMENT IN THE TRACK GUIDANCE...CONFIDENCE IN THE THE
OFFICIAL FORECAST IS LOW BEYOND ABOUT 48 HOURS.
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      26/0300Z 13.8N 102.2W   100 KT
 12HR VT     26/1200Z 13.8N 103.0W    95 KT
 24HR VT     27/0000Z 13.6N 103.7W    90 KT
 36HR VT     27/1200Z 13.6N 104.2W    80 KT
 48HR VT     28/0000Z 13.9N 104.3W    75 KT
 72HR VT     29/0000Z 14.5N 103.0W    55 KT
 96HR VT     30/0000Z 14.8N 102.6W    45 KT
120HR VT     01/0000Z 15.0N 102.5W    40 KT
 
$$
FORECASTER KIMBERLAIN
 
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