ZCZC MIATCDEP5 ALL TTAA00 KNHC DDHHMM 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 NNNN
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