WDPN31 PGTW 040900 SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 04W (CHOI-WAN) WARNING NR 023// RMKS// 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. TROPICAL DEPRESSION 04W (CHOI-WAN), LOCATED APPROXIMATELY 267 NM SOUTH-SOUTHWEST OF TAIPEI, TAIWAN, HAS TRACKED NORTHEASTWARD AT 10 KNOTS OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) SHOWS A BROAD AREA OF CONVECTION ASSOCIATED WITH TS 04W IS NOW TOTALLY OFFSET TO THE SOUTHWEST FROM A FULLY EXPOSED LOW- LEVEL CIRCULATION CENTER (LLCC). THE INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE USING THE MSI LOOP, EXTRAPOLATION FROM A 040221Z METOP-B ASCAT IMAGE, AND THE PGTW SATELLITE FIX. THE INITIAL INTENSITY OF 30KTS IS SET WITH GOOD CONFIDENCE BASED ON THE OVERALL ASSESSMENT OF MULTIPLE AGENCY DVORAK ESTIMATES OF T1.5/25KTS FROM PGTW, RJTD, ADT, AND SATELLITE CONSENSUS (SATCON) OF 38KTS, REFLECTING THE WEAKENING STATE OF THE CYCLONE. THE SYSTEM RESIDES IN A FAVORABLE ENVIRONMENT WITH GOOD WESTWARD AND EQUATORWARD OUTFLOW, VERY WARM (30-31C) SEA SURFACE TEMPERATURES, AND LOW (05-10KTS) VERTICAL WIND SHEAR (VWS) FROM THE NORTHEAST. THE CYCLONE IS TRACKING ALONG THE WESTERN PERIPHERY OF THE SUBTROPICAL RIDGE (STR) TO THE EAST. 3. FORECAST REASONING. A. THERE IS NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS PROGNOSTIC REASONING MESSAGE. B. TS 04W WILL CONTINUE MOVING TO THE NORTHEAST ALONG THE AFOREMENTIONED STR AND INTERACT SLIGHTLY WITH THE SOUTHERN PORTION OF THE CHUNGYANG MOUNTAIN RANGE IN TAIWAN. BY TAU 24, THE SYSTEM WILL BEGIN DISSIPATING AS IT INTERACTS WITH THE MEI-YU FRONTAL BOUNDARY APPROACHING FROM THE WEST AND REACH FULL DISSIPATION BY TAU 36, OR POSSIBLY SOONER. NUMERICAL MODELS ARE IN TIGHT AGREEMENT FROM 24NM AT TAU 12 TO A MERE 74NM BY TAU 36, LENDING HIGH CONFIDENCE TO THE JTWC TRACK FORECAST.// NNNN