WDPN31 PGTW 081500 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 24W (TWENTYFOUR) WARNING NR 001// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. TROPICAL DEPRESSION 24W (TWENTYFOUR), LOCATED APPROXIMATELY 548 NM EAST-SOUTHEAST OF DA NANG, VIETNAM, HAS TRACKED WESTWARD AT 16 KNOTS OVER THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED SATELLITE IMAGERY DEPICTS A RELATIVELY DISORGANIZED, BUT CONSOLIDATING SYSTEM, WITH FLARING CONVECTION OBSCURING THE LOW LEVEL CIRCULATION CENTER (LLCC). THE INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE BASED ON LATE RECEIPT OF A PARTIAL 081218Z ASCAT-B PASS, WHICH SHOWS THAT THE WELL DEFINED LLCC IS TUCKED UNDER THE FLARING DEEP CONVECTION. THE INITIAL INTENSITY OF 25 KTS IS ASSESSED WITH HIGH CONFIDENCE BASED ON MULTI-AGENCY DVORAK CURRENT INTENSITY ESTIMATES OF T1.5 (25 KTS) FROM PGTW AND RJTD, WITH CONFIRMATION PROVIDED BY THE 081218Z ASCAT- B PASS THAT DEPICTS 20-25 KTS IN THE NORTHWEST QUADRANT OF THE SYSTEM. TD 24W IS TRACKING ALONG THE SOUTHERN PERIPHERY OF A SUBTROPICAL RIDGE (STR) POSITIONED TO THE NORTH AND THROUGH A WEAKLY FAVORABLE ENVIRONMENT FOR FURTHER DEVELOPMENT WITH WARM (29-30 CELSIUS) SEA SURFACE TEMPERATURES (SST), LOW TO MODERATE (10-15 KTS) VERTICAL WIND SHEAR (VWS), AND SINGLE CHANNEL WESTWARD OUTFLOW. 3. FORECAST REASONING. A. THIS IS THE FIRST PROGNOSTIC REASONING MESSAGE AND SETS THE FORECAST PHILOSOPHY. B. TD 24W WILL TRACK WESTWARD THROUGH THE ENTIRE FORECAST PERIOD ALONG THE SOUTHERN PERIPHERY OF THE DEEP-LAYER STR TO THE NORTH. FORWARD TRACK SPEED IS FORECAST TO DECREASE AFTER TAU 24 AS THE STR WEAKENS AND THE GRADIENT SLACKENS SLIGHTLY. AS THE SYSTEM TRACKS WEST, ENVIRONMENTAL CONDITIONS REMAIN UNCHANGED THROUGH THE FIRST 36 HOURS, BUT VWS WILL SLACKEN SOMEWHAT, ALLOWING FOR A BURST OF INTENSIFICATION, PEAKING AT 40 KNOTS BY TAU 24, JUST BEFORE THE SYSTEM IS FORECAST TO MAKE LANDFALL ALONG THE SOUTH-CENTRAL VIETNAM COAST AT OR NEAR TAU 36. AFTER THIS POINT, 24W WILL RAPIDLY WEAKEN DUE TO INTERACTION WITH THE RUGGED TERRAIN, DISSIPATING BY TAU 72 OVER CENTRAL CAMBODIA. NUMERICAL MODEL TRACK GUIDANCE IS IN TIGHT AGREEMENT WITH NAVGEM REPRESENTING THE POLEWARD EDGE OF THE ENVELOPE, AND GFS THE EQUATORWARD, BUT OVERALL SPREAD IS LESS THAN 100 NM, LENDING HIGH CONFIDENCE TO THE JTWC TRACK WHICH LIES CLOSE TO THE MULTI-MODEL CONSENSUS.// NNNN