WDPN31 PGTW 210900 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 19W (SAUDEL) WARNING NR 010// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. TROPICAL STORM (TS) 19W (SAUDEL), LOCATED APPROXIMATELY 174 NM NORTHWEST OF MANILA, PHILIPPINES, HAS TRACKED WESTWARD AT 04 KNOTS (KTS) OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY SHOWS A CONSOLIDATING LOW LEVEL CIRCULATION CENTER (LLCC) WITH DEEP CONVECTIVE BANDING OVER THE WESTERN SEMICIRCLE. A 210722Z SSMI 37 GHZ MICROWAVE IMAGE INDICATES A BROAD MICROWAVE EYE FEATURE WITH BANDING WRAPPING AROUND THE SYSTEM, LENDING GOOD CONFIDENCE TO THE INITIAL POSITION. THE INITIAL INTENSITY REMAINS AT 45 KTS BASED ON DVORAK INTENSITY ESTIMATES OF T3.0/3.5 (45-55 KTS) BY PGTW AND KNES AND T3.0/3.0 (45 KTS) BY RJTD. TS 19W IS TRANSITING THROUGH AN OVERALL FAVORABLE ENVIRONMENT CHARACTERIZED BY NEAR-RADIAL UPPER LEVEL OUTFLOW, LOW (10-15 KT) VERTICAL WIND SHEAR (VWS), AND WARM (29-30 CELSIUS) SEA SURFACE TEMPERATURES (SST), MAKING THE REGION CONDUCIVE FOR CONTINUED DEVELOPMENT. A SHORTWAVE TROUGH CURRENTLY DIGGING OVER SOUTHEAST CHINA HAS BEGUN TO WEAKEN THE STEERING SUBTROPICAL RIDGE (STR), CAUSING TS 19W TO SLOW AS IT ENTERS A WEAKENED STEERING ENVIRONMENT WITH A COL FORMING TO THE NORTH. 3. FORECAST REASONING. A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS PROGNOSTIC REASONING MESSAGE. B. IN THE NEAR TERM, THE SYSTEM WILL BEGIN TO SLOWLY TURN WEST- NORTHWESTWARD THEN NORTHWESTWARD AS THE SHORTWAVE TROUGH FURTHER WEAKENS THE STR AND THE AFOREMENTIONED COL FORMS NORTH OF THE SYSTEM. THERE IS SOME UNCERTAINTY DURING THIS PORTION OF THE FORECAST DUE TO VARIATIONS IN THE TIMING OF THE SHORTWAVE TROUGH APPROACH. THE MAJORITY OF THE NUMERICAL MODEL GUIDANCE IS IN FAIR AGREEMENT WITH SOME DIFFERENCES TIMING AND DURATION OF THE POLEWARD TURN. AFTER TAU 48, THE SHORTWAVE TROUGH IS EXPECTED TO PROPAGATE EASTWARD WHICH WILL CAUSE THE STR TO REBUILD. THE SYSTEM WILL THEN RESUME ITS WESTWARD TRACK ALONG THE SOUTHERN PERIPHERY OF THE STR. CONTINUED FAVORABLE ENVIRONMENTAL CONDITIONS INDICATE THAT TS 19W SHOULD INTENSIFY TO A PEAK OF 60 KTS BY TAU 48. C. IN THE EXTENDED FORECAST, TS 19W WILL TRACK WESTWARD AND GRADUALLY WEAKEN AS IT INTERACTS WITH HAINAN ISLAND AND EASTERN VIETNAM. LANDFALL IN EASTERN VIETNAM IS EXPECTED PRIOR TO TAU 120. THERE IS MODERATE CONFIDENCE IN THE JTWC FORECAST TRACK DUE TO THE COMPLEX STEERING ENVIRONMENT AND DYNAMIC SYNOPTIC PATTERN.// NNNN