000 WTPZ45 KNHC 232036 TCDEP5 TROPICAL STORM DARBY DISCUSSION NUMBER 4 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL EP052010 200 PM PDT WED JUN 23 2010 CONVECTIVE BANDING HAS CONTINUED TO INCREASE MARKEDLY AND A BANDING EYE HAS OCCASIONALLY BEEN EVIDENT IN BOTH VISIBLE AND MICROWAVE IMAGERY. UPPER-LEVEL OUTFLOW HAS ALSO BEEN IMPROVING...ESPECIALLY IN THE WESTERN SEMICIRCLE. THE INITIAL INTENSITY IS INCREASED TO 55 KT BASED ON AN INTENSITY ESTIMATE OF T3.5/55 KT FROM SAB. THE INITIAL MOTION ESTIMATE IS 285/10. THERE IS NO CHANGE TO THE PREVIOUS FORECAST REASONING. THE FUTURE TRACK OF DARBY CONTINUES TO WEIGH HEAVILY UPON THE DEVELOPMENT OF A DISTURBANCE LOCATED OVER THE WEST-CENTRAL CARIBBEAN SEA. THE MAJORITY OF THE MODELS... ESPECIALLY THE ECMWF...CONTINUE TO DEVELOP THE CARIBBEAN SEA DISTURBANCE TO VARIOUS DEGREES OVER THE NEXT 5 DAYS AND MOVE THAT SYSTEM INTO THE SOUTHERN GULF OF MEXICO. THIS RESULTS IN WEAKENING OF THE SUBTROPICAL RIDGE TO THE NORTH OF DARBY BY 96-120 HOURS AND CAUSES A DECREASE IN THE STEERING FLOW. BOTH THE GFS AND GFS-PARALLEL RUNS TAKE A RATHER ANEMIC LOOKING DARBY QUICKLY WESTWARD...WHICH ONCE AGAIN APPEARS TO BE DUE TO POOR MODEL INITIALIZATION. AS A RESULT...LESS WEIGHT HAS BEEN PLACED ON THOSE MODELS...WITH MORE WEIGHT BEING PLACED ON THE ECMWF...NOGAPS... UKMET...AND CANADIAN MODELS. DARBY APPEARS TO ALREADY BE ABOUT 12 HOURS INTO A RAPID INTENSIFICATION PHASE. THIS TREND IS FORECAST TO CONTINUE FOR ANOTHER 12 HOURS OR SO WITH SLOWER DEVELOPMENT AFTER THAT. A 23/1606Z TRMM OVERPASS INDICATED THAT THE EARLIER OBSERVED SLIGHT WESTWARD TILT OF THE INNER CORE VORTEX COLUMN HAD DIMINISHED... WHICH WOULD INDICATE THAT DARBY HAS BETTER VERTICAL STRUCTURE THAT IS CONDUCIVE FOR CONTINUED STRENGTHENING. THE SHIPS MODEL SHOWS LESS THAN 5 KT OF VERTICAL SHEAR THROUGH 48 HOURS...WHICH WOULD ALSO SUPPORT CONTINUED STRENGTHENING...AND IT IS QUITE POSSIBLE THAT DARBY COULD BE A MAJOR HURRICANE BY THAT TIME. BY 96 HOURS... THE VERTICAL SHEAR IS EXPECTED TO INCREASE...BUT MUCH LESS NOW THAN PREVIOUS EXPECTED. THE OFFICIAL INTENSITY FORECAST IS HIGHER THAN THE PREVIOUS ADVISORY AND IS BASED ON A BLEND OF THE SHIPS AND LGEM INTENSITY MODELS. FORECAST POSITIONS AND MAX WINDS INITIAL 23/2100Z 12.0N 96.1W 55 KT 12HR VT 24/0600Z 12.3N 97.2W 70 KT 24HR VT 24/1800Z 12.7N 98.8W 80 KT 36HR VT 25/0600Z 13.0N 100.0W 85 KT 48HR VT 25/1800Z 13.4N 101.0W 90 KT 72HR VT 26/1800Z 14.0N 102.0W 90 KT 96HR VT 27/1800Z 14.5N 102.1W 90 KT 120HR VT 28/1800Z 15.0N 102.1W 75 KT $$ FORECASTER STEWART