WDPN31 PGTW 200300 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 19W (SAUDEL) WARNING NR 005// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. TROPICAL STORM (TS) 19W (SAUDEL), LOCATED APPROXIMATELY 234 NM EAST-NORTHEAST OF MANILA, PHILIPPINES, HAS TRACKED WEST- NORTHWESTWARD AT 13 KNOTS OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY DEPICTS A PARTIALLY-EXPOSED, SLOWLY- CONSOLIDATING SYSTEM WITH BROAD CONVECTIVE BANDING WRAPPING INTO A RAGGED LOW-LEVEL CIRCULATION CENTER (LLCC). A 192243Z MHS 89GHZ MICROWAVE IMAGE INDICATES FRAGMENTED BANDING WRAPPING INTO A WEAKLY- DEFINED LLCC. THE INITIAL INTENSITY IS ASSESSED AT 35 KNOTS BASED ON DVORAK INTENSITY ESTIMATES OF T2.5 (35 KNOTS) FROM PGTW AND RJTD. UPPER-LEVEL ANALYSIS REVEALS A FAVORABLE ENVIRONMENT WITH NEAR- RADIAL OUTFLOW AND LOW VERTICAL WIND SHEAR. SST VALUES (29-30C) REMAIN CONDUCIVE. TS 19W IS TRACKING WEST-NORTHWESTWARD ALONG THE SOUTHWEST 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 WESTWARD TO WEST-NORTHWESTWARD UNDER THE STEERING INFLUENCE OF THE STR THROUGH TAU 72, HOWEVER, THE SYSTEM IS EXPECTED TO SLOW FROM TAU 48 TO TAU 72 AS THE STR WEAKENS TEMPORARILY. THIS WEAKENING OF THE STR IS DUE TO AN APPROACHING BROAD MIDLATITUDE SHORTWAVE TROUGH, WHICH IS FORECAST TO DIG OVER SOUTHEAST CHINA. NUMERICAL MODEL GUIDANCE AND THE 19/12Z ECMWF ENSEMBLE INDICATE POTENTIAL FOR THIS SLOW-DOWN WITH A POSSIBLE SHORT- TERM NORTH-NORTHWESTWARD TO NORTHWESTWARD TURN. TS 19W IS FORECAST TO MAINTAIN TROPICAL STORM STRENGTH PRIOR TO MAKING LANDFALL ALONG THE EAST COAST OF LUZON NEAR TAU 12 AND WILL INTENSIFY AS IT REEMERGES OVER THE SOUTH CHINA SEA NEAR TAU 24. THE SYSTEM IS EXPECTED TO INTENSIFY MORE SIGNIFICANTLY AFTER TAU 24 TO AN INTENSITY OF 55 KNOTS BY TAU 72 UNDER FAVORABLE CONDITIONS. C. IN THE EXTENDED PERIOD, THE AFOREMENTIONED SHORTWAVE TROUGH WILL PROPAGATE EASTWARD ALLOWING THE STR TO REBUILD TO THE NORTH. CONSEQUENTLY, TS 19W WILL ACCELERATE WESTWARD THROUGH TAU 120 WHILE INTENSIFYING TO A PEAK INTENSITY OF 60 KNOTS BY TAU 96. SLIGHT WEAKENING IS ANTICIPATED NEAR TAU 120 AS THE SYSTEM BEGINS TO INTERACT WITH HAINAN ISLAND. DUE TO THE COMPLEX, EVOLVING SYNOPTIC PATTERN, THERE IS MODERATE CONFIDENCE IN THE JTWC FORECAST TRACK.// NNNN