ZCZC MIATCDEP5 ALL TTAA00 KNHC DDHHMM 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 NNNN
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