WDPN31 PGTW 180300 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 11W (SON-TINH) WARNING NR 11// RMKS// 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. TROPICAL STORM 11W (SON-TINH), LOCATED APPROXIMATELY 236 NM NORTHEAST OF DA NANG, VIETNAM, HAS TRACKED WESTWARD AT 21 KNOTS OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY SHOWS A COMPACT SYSTEM THAT HAS MAINTAINED ITS BANDING AND STRUCTURE AS IT PASSED OVER HAINAN ISLAND. THE INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE BASED ON A 172337Z SSMIS 91GHZ IMAGE. THE INITIAL INTENSITY WAS MAINTAINED AT 35 KNOTS, WHICH IS UNDER CURRENT INTENSITY ESTIMATES OF T3.0 (45 KTS) AND T3.5 (55 KTS), AND UNDER A 171827Z SATCON ESTIMATE OF 51 KTS. THOSE HIGHER FIX INTENSITIES REFLECT IMPROVED FLARING CONVECTION COMPARED TO 6 HOURS PRIOR. HOWEVER, LOCAL OBSERVATIONS FROM 30-45 NM AWAY FROM THE CENTER DO NOT REFLECT ANYWHERE NEAR THESE HIGHER WIND SPEEDS, AND SHOW A CENTRAL PRESSURE OF APPROXIMATELY 997 MB. ENVIRONMENTAL ANALYSIS REVEALS TS 11W HAS MOVED INTO AN AREA OF UNFAVORABLE VWS (25-30 KTS). UPPER LEVEL WINDS ARE PROVIDING MODERATE EQUATORWARD OUTFLOW AND POLEWARD OUTFLOW IS BEING STIFLED BY THE STR TO THE NORTH, LIMITING DEVELOPMENT POTENTIAL. SEA SURFACE TEMPERATURES ARE VERY WARM IN THE GULF OF TONKIN, RANGING BETWEEN 28 AND 30 DEGREES CELSIUS. TS 11W IS TRACKING QUICKLY WESTWARD BELOW THE SUBTROPICAL RIDGE (STR) WHICH IS LOCATED TO THE NORTHEAST. 3. FORECAST REASONING. A. THERE IS NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS PROGNOSTIC REASONING MESSAGE. B. TS 11W WILL CONTINUE RAPIDLY TRACKING WESTWARD ALONG THE SOUTHERN EXTENT OF THE STR LOCATED TO THE NORTHEAST. AFTER CROSSING HAINAN ISLAND, VERY WARM SSTS IN THE GULF OF TONKIN WILL COUNTERACT THE HIGHER VWS AND LIMITED OUTFLOW TO HELP TS 11W MAINTAIN AN INTENSITY OF 35 KNOTS THROUGH TAU 12, BEFORE IT MAKES LANDFALL IN NORTHERN VIETNAM, AFTER WHICH IT WILL RAPIDLY WEAKEN. THE JTWC FORECAST TRACK IS PLACED FASTER THAN THE MULTI-MODEL CONSENSUS DUE TO THE FORECASTED ACCELERATION FOR TS 11W. DYNAMIC MODEL GUIDANCE IS IN TIGHT AGREEMENT, THEREFORE THERE IS HIGH CONFIDENCE IN THE JTWC FORECAST TRACK.// NNNN