ZCZC MIATCDEP5 ALL TTAA00 KNHC DDHHMM TROPICAL STORM DARBY DISCUSSION NUMBER 3 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL EP052010 800 AM PDT WED JUN 23 2010 THE CONVECTIVE ORGANIZATION OF DARBY HAS INCREASED SHARPLY DURING THE PAST 6 HOURS AS STRONGLY CURVED BANDING FEATURES HAVE DEVELOPED. IN FACT...RECENT VISIBLE SATELLITE IMAGES HINT THAT A BANDING EYE FEATURE COULD BE FORMING...BUT THIS MAY JUST BE A SMALL DRY SLOT THAT HAS DEVELOPED. INTENSITY ESTIMATES ARE T3.0 FROM TAFB AND T2.5 FROM SAB. GIVEN THE IMPROVED SATELLITE APPEARANCE SINCE THE 12Z FIXES...THE INITIAL INTENSITY IS SET AT 45 KT. THE INITIAL MOTION ESTIMATE IS 285/08. THE FORECAST TRACK OF DARBY HINGES HEAVILY UPON WHAT HAPPENS TO THE DISTURBANCE LOCATED OVER THE CENTRAL CARIBBEAN SEA. THE GFDL AND HWRF MODELS...PLUS ALL OF THE GLOBAL MODELS EXCEPT FOR THE GFS...DEVELOP THE CARIBBEAN DISTURBANCE TO VARIOUS DEGREES OVER THE NEXT 5 DAYS...WHICH CAUSES THE SUBTROPICAL RIDGE TO THE NORTH OF DARBY TO WEAKEN BY DAYS 3-4. THIS RESULTS IN A WEAKENING OF THE STEERING FLOW...AND SOME OF THE MODELS EVEN FORECAST SOME WEAK BINARY INTERACTION WITH THE DEVELOPING CARIBBEAN DISTURBANCE AFTER THAT SYSTEM ENTERS THE SOUTHERN GULF MEXICO. THE GFS DOES NOT SHOW ANY INTERACTION WITH THE CARIBBEAN DISTURBANCE BECAUSE IT NEITHER DEVELOPS DARBY OR THE OTHER SYSTEM. DUE TO THE POOR 06Z INITIALIZATION AND SHORT TERM FORECAST TRENDS BY THE GFS MODEL...LESS WEIGHT HAS BEEN PLACED ON THAT MODEL AND IT IS CONSIDERED AN OUTLIER. THE OFFICIAL FORECAST MAINTAINS THE PREVIOUS FORECAST TREND OF SLOWING DOWN DARBY IN THE 72-120 HOUR TIME FRAME DUE TO EXPECTED INTERACTION WITH THE LARGE CARIBBEAN SYSTEM...REGARDLESS OF WHETHER OR NOT THAT SYSTEM GOES ON TO BECOME A TROPICAL CYCLONE. THE RECENT SHARP INTENSIFICATION TREND WOULD SUGGEST THAT DARBY MAY BE IN THE EARLY STAGES OF RAPID INTENSIFICATION. HOWEVER...DESPITE THE IMPROVED BANDING FEATURES...CLOUD TOPS IN THE INNER CORE REGION HAVE WARMED SUGGESTING THAT DRY AIR MAY BE ACTING TO ERODE THE CENTRAL DEEP CONVECTION. THE GFS-BASED SHIPS MODEL INDICATES THAT THE VERTICAL SHEAR WILL DECREASE TO LESS THAN 5 KNOTS OVER THE COURSE OF THE NEXT 36 HOURS...WHICH WOULD STRONGLY FAVOR RAPID INTENSIFICATION. THE OFFICIAL FORECAST TRACK IS A BLEND OF THE SHIPS AND PREVIOUS FORECAST IN CASE THE EROSION OF THE INNER CORE CONVECTION CONTINUES...AND ALSO TO MAINTAIN SOME CONTINUITY WITH THE PREVIOUS ADVISORY. HOWEVER...THE SHIPS MODEL IS INDICATING A GREATER THAN 40 PERCENT CHANCE OF RAPID INTENSIFICATION OCCURRING...AND THIS SCENARIO WILL BE CLOSELY ASSESSED FOR THE NEXT ADVISORY PACKAGE. FORECAST POSITIONS AND MAX WINDS INITIAL 23/1500Z 11.8N 94.8W 45 KT 12HR VT 24/0000Z 12.2N 95.9W 50 KT 24HR VT 24/1200Z 12.6N 97.4W 60 KT 36HR VT 25/0000Z 12.9N 98.8W 65 KT 48HR VT 25/1200Z 13.2N 99.8W 70 KT 72HR VT 26/1200Z 13.7N 101.1W 70 KT 96HR VT 27/1200Z 14.2N 101.5W 70 KT 120HR VT 28/1200Z 14.7N 101.5W 65 KT $$ FORECASTER STEWART NNNN
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