MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 04W (SINLAKU) WARNING NR 003// RMKS// 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. TROPICAL STORM 04W (SINLAKU), LOCATED APPROXIMATELY 138 NM SOUTH-SOUTHEAST OF HANOI, VIETNAM, HAS TRACKED WESTWARD AT 09 KNOTS OVER THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED SATELLITE IMAGERY DEPICTS FRAGMENTED DEEP CONVECTIVE BANDING OVER THE WESTERN SEMICIRCLE WITH A BROAD LOW-LEVEL CIRCULATION CENTER (LLCC). THE INITIAL INTENSITY IS SET AT 35 KNOTS BASED ON SUBJECTIVE AND OBJECTIVE DVORAK INTENSITY ESTIMATES RANGING FROM T1.5 TO T2.7 (25 TO 39 KNOTS) AND A 011421Z PARTIAL ASCAT-B PASS WHICH REVEALS A SMALL SWATH OF 30-34 KT WINDS TO THE SOUTH OF THE LLCC. WIND RADII HAVE BEEN UPDATED BASED ON RECENT ASCAT DATA. THE ENVIRONMENT IS MARGINALLY FAVORABLE WITH HIGH (>25 KTS) NORTHEASTERLY VERTICAL WIND SHEAR (VWS) OFFSETTING THE WARM SEA SURFACE TEMPERATURES AND GOOD UPPER LEVEL OUTFLOW. TS 04W IS CURRENTLY TRACKING WESTWARD ALONG THE PERIPHERY OF THE LOW- TO MID-LEVEL SUBTROPICAL RIDGE (STR) POSITIONED TO THE NORTH. 3. FORECAST REASONING. A. NO CHANGE IN FORECAST PHILOSOPHY SINCE THE PREVIOUS PROGNOSTIC REASONING MESSAGE. B. TS 04W IS FORECAST TO TRACK WEST-NORTHWESTWARD THROUGHOUT THE FORECAST PERIOD, MAKING LANDFALL OVER VIETNAM PRIOR TO TAU 12. AS THE SYSTEM TRANSITS OVER THE WARM WATERS (29-30 CELSIUS) OF THE GULF OF TONKIN, TS 40W IS EXPECTED TO SLOWLY WEAKEN DUE TO PERSISTENT NORTHEASTERLY VERTICAL WIND SHEAR (25-30 KTS). PRIOR TO TAU 12, THE SYSTEM WILL BEGIN TO INTERACT WITH LAND AND STEADILY WEAKEN. THEN THE SYSTEM WILL TRACK INLAND AND DISSIPATE OVER MOUNTAINOUS TERRAIN BY TAU 36. NUMERICAL MODEL GUIDANCE IS IN STRONG AGREEMENT, PLACING GOOD CONFIDENCE IN THE JTWC FORECAST TRACK WHICH IS PLACED NEAR THE MULTI- MODEL CONSENSUS.// NNNN NNNN