WDPN31 PGTW 260300 MSGID/GENADMIN/NAVMARFCSTCEN PEARL HARBOR HI/JTWC// SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 17W (SEVENTEEN) WARNING NR 05// RMKS// 1. FOR METEOROLOGISTS. 2. 12 HOUR SUMMARY AND ANALYSIS. A. TROPICAL STORM (TS) 17W HAS INTENSIFIED AS EVIDENCED BY DEEPENED CONVECTION ON THE WESTERN FLANK OF THE SYSTEM ALTHOUGH THE LOW LEVEL CIRCULATION CENTER (LLCC) HAS BECOME FULLY EXPOSED. THE STORM IS ABOUT TO MAKE LANDFALL INTO LUZON AS IT TRACKS WESTWARD ALONG THE SOUTHERN PERIPHERY OF THE LOW- TO MID-LEVEL SUBTROPICAL RIDGE TO THE NORTH. ANIMATED WATER VAPOR IMAGERY SHOWS EXCELLENT POLEWARD OUTFLOW OVER THE SYSTEM DESPITE AN EASTERLY VERTICAL WIND SHEAR ERODING THE SOUTH- EASTERN QUADRANT OF THE STORM. THE CURRENT INTENSITY OF 35 KNOTS IS BASED ON DVORAK ESTIMATES FROM PGTW, KNES, AND RJTD RANGING FROM T2.0 TO T2.5. THE CURRENT POSITION IS BASED ON MULTIPLE AGENCY FIXES AND FROM A 252342Z SSMIS MICROWAVE IMAGE WITH A FAIR DEGREE OF CONFIDENCE. 3. FORECAST REASONING. A. THERE IS A MINOR CHANGE IN THE FORECAST PHILOSOPHY FROM THE PREVIOUS BULLETIN, AS DESCRIBED BELOW. B. TS 17W IS EXPECTED TO MAINTAIN A WESTWARD TRAJECTORY THROUGH THE INITIAL 36 HOURS OF THE FORECAST BEFORE IT TRACKS SLOWER AND SLIGHTLY NORTH OF WEST IN RESPONSE TO AN APPROACHING MID-LATITUDE TROUGH FROM THE CHINESE INTERIOR. IN ADDITION TO THE TRACK DEVIATION, THE STORM WILL ALSO BECOME STRONGER THAN PREVIOUSLY ANTICIPATED DUE TO WARMER ALONG-TRACK SEA SURFACE TEMPERATURES (WELL IN EXCESS OF 30C) BETWEEN HAINAN AND THE PHILIPPINES. C. AFTER TAU 72, TS 17W WILL BRUSH THE SOUTHERN COAST OF HAINAN, CROSS THE GULF OF TONKIN, AND MAKE LANDFALL SOUTH OF HANOI, VIETNAM BEFORE IT DISSIPATES AS A SIGNIFICANT TROPICAL CYCLONE OVER LAND. THE SYSTEM WILL MAINTAIN TROPICAL STORM INTENSITY THROUGHOUT THIS PERIOD DUE TO CONTINUED FAVORABLE CONDITIONS, HOWEVER, IT WILL WEAKEN AFTER TAU 96 DUE TO ITS INTERACTION WITH HAINAN'S TOPOGRAHY. THE AVAILABLE NUMERICAL GUIDANCE ARE IN FAIR AGREEMENT WITH THIS FORECAST UP TO TAU 36 BEFORE THEY SPLIT IN TWO DISTINCT BANDS. THE NORTHERN BAND INCLUDES ECMWF, NOGAPS, AND GFS WHILE THE SOUTHERN BAND INCLUDES EGRR AND JGSM. THIS FORECAST RUNS BETWEEN THESE TWO BANDS WITH A SLIGHT LEAN TO THE NORTH.// NNNN