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Tropical Storm DARBY


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TROPICAL STORM DARBY DISCUSSION NUMBER  17
NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL   EP052010
800 PM PDT SAT JUN 26 2010
 
ALTHOUGH THE CLOUD PATTERN ASSOCIATED WITH DARBY IN GEOSTATIONARY
SATELLITE IMAGERY REMAINS REASONABLY WELL ORGANIZED...THERE IS
EVIDENCE THAT DARBY IS BEGINNING TO UNRAVEL RATHER QUICKLY. A 2040
UTC AMSR-E OVERPASS REVEALED A PARTIALLY EXPOSED LOW-LEVEL CENTER
EAST OF A PLUME OF CONVECTION...INDICATING THAT EASTERLY VERTICAL
SHEAR IS TAKING A TOLL ON THE CYCLONE. ADDITIONALLY...THE LAST
VISIBLE IMAGES SUGGEST THAT THE LOW-LEVEL CENTER HAS SEPARATED FROM
THE MID-LEVEL CENTER...BEING DISPLACED BY NEARLY A DEGREE TO THE
NORTHWEST. DVORAK SATELLITE CLASSIFICATIONS ARE 4.0 FROM TAFB AND
SAB BUT CONTINUE TO BE CONSTRAINED BY RULES WHILE 3-HOURLY AVERAGED
UW-CIMSS AODT VALUES ARE AROUND 3.5. GIVEN THE RAPID LOSS IN
ORGANIZATION AND THE LOWER AODT VALUES...THE INITIAL INTENSITY IS
LOWERED TO 60 KT. SHIPS MODEL ANALYSES INDICATE MODERATE EASTERLY
VERTICAL WIND SHEAR OVER DARBY WHICH IS ONLY FORECAST TO BECOME
STRONGER AFTER 24 HOURS...AND SHOULD RESULT IN CONTINUED WEAKENING.
THE OFFICIAL FORECAST CLOSELY FOLLOWS THE SHIPS/LGEM INTENSITY
GUIDANCE...CALLING FOR DARBY BECOME A REMNANT LOW IN 3 DAYS...IF
NOT SOONER.

THE AFOREMENTIONED AMSR-E OVERPASS WAS HELPFUL IN DETERMINING THE
INITIAL MOTION ESTIMATE OF 270/2. DARBY IS EMBEDDED IN A WEAK
WESTERLY LOW-LEVEL FLOW ON THE PERIPHERY OF THE LARGE CIRCULATION
ASSOCIATED WITH TROPICAL STORM ALEX AND STRONGER EASTERLY FLOW
ALOFT. THE RESULTING DEEP-LAYER MEAN FLOW SHOULD CARRY THE CYCLONE
ON A SLOW WESTWARD COURSE FOR THE NEXT 12 HOURS OR SO. THEREAFTER
...AS DARBY WEAKENS FURTHER AND BECOMES A SHALLOWER CYCLONE...IT AND
EVENTUALLY ITS REMNANTS WILL BE DRAWN EAST-NORTHEASTWARD OR
NORTHEASTWARD WITHIN THE DOMINANT CIRCULATION OF ALEX...WHICH IS
FORECAST TO MOVE OVER THE EXTREME SOUTHWESTERN GULF OF MEXICO
DURING THE NEXT FEW DAYS. THE NEW FORECAST TRACK IS ADJUSTED
SHARPLY TO THE RIGHT RIGHT...BUT NOT AS FAR RIGHT AS THE
MULTI-MODEL CONSENSUS...TO ACCOUNT FOR A SIGNIFICANT EASTWARD
SHIFT IN THE MODEL GUIDANCE.
 
FORECAST POSITIONS AND MAX WINDS
 
INITIAL      27/0300Z 13.5N 103.0W    60 KT
 12HR VT     27/1200Z 13.5N 103.3W    45 KT
 24HR VT     28/0000Z 13.7N 103.2W    40 KT
 36HR VT     28/1200Z 14.0N 102.7W    35 KT
 48HR VT     29/0000Z 14.4N 102.0W    30 KT
 72HR VT     30/0000Z 15.0N 101.0W    25 KT...POST-TROP/REMNT LOW
 96HR VT     01/0000Z...DISSIPATED
 
$$
FORECASTER KIMBERLAIN
 
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