WDPN31 PGTW 200900 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 19W (SAUDEL) WARNING NR 006// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. TROPICAL STORM (TS) 19W (SAUDEL), LOCATED APPROXIMATELY 149 NM EAST-NORTHEAST OF MANILA, PHILIPPINES, HAS TRACKED WESTWARD AT 17 KNOTS (KTS) OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY DEPICTS A PARTIALLY-EXPOSED SYSTEM WITH BROAD CONVECTIVE BANDING WRAPPING INTO A CONSOLIDATING LOW-LEVEL CIRCULATION CENTER (LLCC) FROM THE NORTH. A 200737Z SSMI 85 GHZ MICROWAVE IMAGE SHOWS DEEP CONVECTION OVER THE WESTERN SEMI-CIRCLE WITH FRAGMENTED BANDING WRAPPING INTO A DEFINED LLCC. THE INITIAL INTENSITY IS ASSESSED AT 40 KNOTS BASED ON DVORAK INTENSITY ESTIMATES OF T2.5-3.0 (35-45 KTS) FROM PGTW AND RJTD. NEAR-RADIAL UPPER LEVEL OUTFLOW, LOW (10-15 KT) VERTICAL WIND SHEAR (VWS), AND WARM (29-30 CELSIUS) SEA SURFACE TEMPERATURES (SST) CONTRIBUTE TO AN OVERALL FAVORABLE ENVIRONMENT FOR CONTINUED DEVELOPMENT. TS 19W IS TRACKING ALONG THE PERIPHERY OF A DEEP-LAYERED SUBTROPICAL RIDGE (STR) POSITIONED TO THE NORTHEAST WITH AN EXTENSION OF THE STR TO THE NORTH. 3. FORECAST REASONING. A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS PROGNOSTIC REASONING MESSAGE. B. TS 19W WILL CONTINUE TRACKING GENERALLY WESTWARD UNDER THE STEERING INFLUENCE OF THE STR THROUGH TAU 72. HOWEVER, THE SYSTEM IS EXPECTED TO SLOW FROM TAU 36 TO TAU 72 AS THE STR TEMPORARILY WEAKENS DUE TO THE APPROACH OF A MIDLATITUDE SHORTWAVE TROUGH WHICH IS EXPECTED TO DIG OVER SOUTHEAST CHINA. DURING THIS TIME, MODEL GUIDANCE AND THE 19/00Z ECMWF ENSEMBLE INDICATE A SHORT-TERM NORTH- NORTHWESTWARD TO NORTHWESTWARD TRACK DUE TO THE LACK OF STEERING GUIDANCE. THE NAVGEM AND ECMWF MODEL SOLUTIONS PRESENT THE MOST AGGRESSIVE NORTH-NORTHWESTWARD TRACK SOLUTIONS AT THIS TIME, TRACKING TS 19W FURTHER NORTH THAN THE CURRENT JTWC TRACK FORECAST. THE JTWC TRACK FORECAST LIES NEAR THE MULTI-MODEL CONSENSUS. THE SYSTEM IS EXPECTED TO MAINTAIN ITS INTENSITY AS IT MAKES LANDFALL IN LUZON NEAR TAU 6 THEN INTENSIFY AS IT REEMERGES OVER THE SOUTH CHINA SEA NEAR TAU 12-18. AFTERWARDS, TS 19W SHOULD STEADILY INTENSIFY TO A PEAK OF 60 KTS BY TAU 72 UNDER FAVORABLE CONDITIONS. C. AS THE AFOREMENTIONED SHORTWAVE TROUGH PROPAGATES EASTWARD, THE STR WILL REBUILD TO THE NORTH, ALLOWING TS 19W TO ACCELERATE WESTWARD ALONG ITS SOUTHERN PERIPHERY. ALONG THIS TRACK, THE SYSTEM WILL MAINTAIN INTENSITY UNTIL IT BEGINS TO INTERACT WITH HAINAN ISLAND AND BEGINS TO WEAKEN SLIGHTLY. DUE TO THE COMPLEX STEERING ENVIRONMENT AND DYNAMIC SYNOPTIC PATTERN, THERE IS MODERATE CONFIDENCE IN THE JTWC FORECAST TRACK.// NNNN