ZCZC MIATCDEP1 ALL TTAA00 KNHC DDHHMM TROPICAL STORM HILDA DISCUSSION NUMBER 3 NWS TPC/NATIONAL HURRICANE CENTER MIAMI FL EP112009 800 PM PDT SAT AUG 22 2009 THE SATELLITE PRESENTATION OF HILDA HAS NOT BEEN VERY IMPRESSIVE DURING THE PAST SEVERAL HOURS...AS THE CENTER HAS BEEN EXPOSED MOST OF THE TIME. HOWEVER...NEW CONVECTION HAS BEEN FORMING TO THE NORTH AND WEST OF THE CENTER AND AN EARLIER ASCAT MICROWAVE PASS AT 1912 UTC INDICATED THAT THE WINDS WERE NEAR TROPICAL STORM FORCE AT THAT TIME. THE INITIAL INTENSITY WILL BE KEPT AT 35 KT FOR THIS ADVISORY...IN GOOD AGREEMENT WITH THE DVORAK CI NUMBERS FROM BOTH TAFB AND SAB AND THE ASCAT DATA. THE INTENSITY FORECAST FOR HILDA IS A BIT PERPLEXING...WITH LOTS OF MIXED SIGNALS. ON ONE HAND...VERTICAL WIND SHEAR IS FORECAST TO BE MODERATE FOR THE NEXT FEW DAYS...WHICH SHOULD HINDER DEVELOPMENT. WATER VAPOR IMAGERY ALSO SHOW SOME MID- TO UPPER-LEVEL DRY AIR NEAR THE CENTER OF HILDA...WHICH COULD PREVENT SUSTAINED DEEP CONVECTION...ESPECIALLY IN A SHEARED ENVIRONMENT. DESPITE THE MARGINAL ATMOSPHERIC CONDITIONS...ALL GUIDANCE IS SHOWING SLOW STRENGTHENING...WITH EVERY MODEL CLOSE TO OR AT HURRICANE STRENGTH BY 120 HOURS. IF THIS SYSTEM SURVIVES THE MARGINAL ENVIRONMENT FOR THE NEXT COUPLE OF DAYS...THE GLOBAL MODELS SHOW THE SHEAR RELAXING AND A MORE SIGNIFICANT INTENSIFICATION COULD OCCUR AFTER THAT TIME. GIVEN THE ABOVE FACTORS...THE NHC INTENSITY FORECAST WILL BE SIMILAR TO THE PREVIOUS ONE AND IS LOWER THAN MUCH OF THE GUIDANCE. THE INITIAL MOTION IS 270/08. WEAK RIDGING APPEARS LIKELY TO STEER THE CYCLONE TO THE WEST OR WEST-NORTHWEST FOR THE DAY OR SO UNTIL HILDA ENCOUNTERS A TROUGH ALONG ABOUT 145W. A DEEPER SYSTEM MIGHT TURN MORE TO THE NORTHWEST IN RESPONSE TO THE TROUGH...BUT HILDA IS NOT EXPECTED TO BE PARTICULARLY STRONG AT THAT TIME. THEREAFTER...THE TROUGH IS FORECAST TO LIFT OUT OF THE REGION WITH WEAK SUBTROPICAL RIDGING EXPECTED TO BUILD NORTHWEST OF HILDA...CAUSING A MORE WESTWARD MOTION. UNDER THE ASSUMPTION THAT HILDA REMAINS WEAK...THE OFFICIAL FORECAST WILL REMAIN ON THE SOUTHERN SIDE OF THE GUIDANCE ENVELOPE...A HAIR SOUTH OF THE PREVIOUS TRACK FORECAST THROUGH 3 DAYS AND BASICALLY THE SAME THEREAFTER. FORECAST POSITIONS AND MAX WINDS INITIAL 23/0300Z 13.6N 138.5W 35 KT 12HR VT 23/1200Z 13.7N 139.8W 35 KT 24HR VT 24/0000Z 14.1N 141.5W 35 KT 36HR VT 24/1200Z 14.5N 143.1W 35 KT 48HR VT 25/0000Z 14.8N 144.8W 40 KT 72HR VT 26/0000Z 15.0N 148.0W 40 KT 96HR VT 27/0000Z 15.0N 151.5W 45 KT 120HR VT 28/0000Z 15.0N 154.0W 55 KT $$ FORECASTER BLAKE NNNN
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Page last modified: Thursday, 31-Dec-2009 12:09:22 UTC