WDPN31 PGTW 041500 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 04W (CHOI-WAN) WARNING NR 024// RMKS// 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. TROPICAL DEPRESSION 04W (CHOI-WAN), LOCATED APPROXIMATELY 187 NM SOUTH OF TAIPEI, TAIWAN, HAS TRACKED NORTHEASTWARD AT 18 KNOTS OVER THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED SATELLITE IMAGERY (EIR) DEPICTS A HEAVILY SHEARED CONVECTIVE STRUCTURE WITH THE LOW- LEVEL CIRCULATION CENTER (LLCC) LOCATED JUST EAST OF SOUTHERN TAIWAN. THE INITIAL POSITION IS PLACED WITH MODERATE CONFIDENCE USING THE EIR LOOP, EXTRAPOLATION FROM WELL-TIMED 041220Z GMI 37 AND 89GHZ IMAGES, AND THE PGTW SATELLITE FIX. THE INITIAL INTENSITY OF 25KTS IS SET WITH FAIR CONFIDENCE BASED ON THE OVERALL ASSESSMENT OF MULTIPLE AGENCY DVORAK ESTIMATES OF T1.5/25KTS FROM PGTW, RJTD, ADT T2.1/31KTS, AND SATELLITE CONSENSUS (SATCON) OF 38KTS, WHICH REFLECTS THE CONTINUAL WEAKENING STATE OF THE CYCLONE. THE SYSTEM RESIDES IN A MARGINALLY FAVORABLE ENVIRONMENT WITH FAIR EQUATORWARD OUTFLOW AND WARM (29-30C) SEA SURFACE TEMPERATURES (SSTS), AND LOW (05-10KTS) VERTICAL WIND SHEAR (VWS) FROM THE NORTHEAST ALONG WITH THE TERRAIN INTERACTION ALONG THE SOUTHERN TIP OF TAIWAN. CHOI-WAN IS TRACKING ALONG THE WESTERN PERIPHERY OF THE SUBTROPICAL RIDGE (STR) TO THE EAST AND IS BEGINNING TO INTERACT WITH THE MEI-YU BOUNDARY TO THE NORTH OVER THE EAST CHINA SEA. 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 STR AND INTERACT WITH THE BAROCLINIC ZONE OF THE MEI-YU BOUNDARY AND BEGIN TO TAP INTO THE POLEWARD OUTFLOW CHANNEL. THE NEW OUTFLOW WILL ALLOW FOR A SLIGHT INTENSIFICATION JUST BEFORE 04W MOVES OVER THE COOLER 25-27C SSTS NEAR THE RYUKU ISLAND CHAIN AND START DISSIPATING THE SYSTEM. 04W WILL ENCOUNTER COOLER 24-26C SEA SURFACE TEMPERATURES BY TAU 24, INHIBITING ANY FURTHER DEVELOPMENT AND COMPLETELY DISSIPATE THE SYSTEM BY TAU 36, IF NOT SOONER. NUMERICAL MODELS REMAIN IN TIGHT AGREEMENT THROUGH TAU 36, LENDING HIGH CONFIDENCE TO THE JTWC TRACK FORECAST.// NNNN