WDPN32 PGTW 251500 MSGID/GENADMIN/NAVMARFCSTCEN PEARL HARBOR HI/JTWC// SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 21W WARNING NR 05// RMKS/ 1. FOR METEOROLOGISTS. 2. 12 HOUR SUMMARY AND ANALYSIS. A. TROPICAL STORM (TS) 21W (HAITANG), LOCATED APPROXIMATELY 255 NM EAST OF HUE, VIETNAM, HAS TRACKED WESTWARD AT 05 KNOTS OVER THE PAST SIX HOURS. ANIMATED INFRARED SATELLITE IMAGERY CONTINUES TO DEPICT A PARTIALLY-EXPOSED LOW-LEVEL CIRCULATION CENTER (LLCC) WITH A LARGE BURST OF DEEP CONVECTION DISPLACED JUST WEST OF THE CENTER DUE TO MODERATE EASTERLY VERTICAL WIND SHEAR (20 KNOTS) AND BROAD DIFFLUENCE ALOFT. A 251247Z SSMIS 37 GHZ IMAGE INDICATES IMPROVED CONVECTIVE BANDING WRAPPING TIGHTLY INTO A DEFINED CENTER. THIS IMAGE SUPPORTS THE CURRENT POSITION AND RECENT TRACK MOTION WITH GOOD CONFIDENCE. THE CURRENT INTENSITY IS ASSESSED HIGHER THAN THE DVORAK ESTIMATES OF 25-30 KNOTS BASED ON A 25/06Z SHIP OBSERVATION, LOCATED 95 NM NORTHEAST OF THE 25/06Z CENTER, WHICH REPORTED 100/37 KNOTS AND SLP OF 999 MB. 3. FORECAST REASONING. A. NO CHANGE TO FORECAST PHILOSOPHY. B. TS 21W IS EXPECTED TO TRACK WESTWARD INTO VIETNAM UNDER THE STEERING INFLUENCE OF THE LOW- TO MID-LEVEL SUBTROPICAL RIDGE POSITIONED (AND BUILDING) NORTH OF HAINAN ISLAND. THE AVAILABLE MODELS ARE IN GOOD AGREEMENT. TS 21W IS EXPECTED TO REMAIN A WEAK SYSTEM (30-35 KNOTS) DUE TO MARGINAL UPPER-LEVEL CONDITIONS AND WILL DISSIPATE OVER LAND BY TAU 48.// NNNN