WDPN31 PGTW 022100 SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 04W (CHOI-WAN) WARNING NR 017// RMKS// 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. TROPICAL DEPRESSION (TD) 04W (CHOI-WAN), LOCATED APPROXIMATELY 72 NM WEST-NORTHWEST OF MANILA, PHILIPPINES, HAS TRACKED NORTHWESTWARD AT 14 KNOTS OVER THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED SATELLITE IMAGERY (EIR) SHOWS TD 04W (CHOI-WAN) BECOMING SLIGHTLY DISORGANIZED IN THE EASTERN PERIPHERY DUE TO INTERACTION WITH THE PHILIPPINES WITH DEEP CONVECTION TO THE NORTHWEST AND SOUTH OF THE LOW LEVEL CIRCULATION CENTER (LLCC). THE INITIAL POSITION IS PLACED WITH FAIR CONFIDENCE BASED ON LOW CLOUD TRACING IN THE EIR LOOP AND SHORE-BASED WEATHER OBSERVATIONS FROM MANILLA AND SUBIC BAY. THE INITIAL INTENSITY OF 30KTS IS SET WITH FAIR CONFIDENCE BASED ON THE AFOREMENTIONED OBSERVATIONS AND AN OVERALL ASSESSMENT OF DVORAK ESTIMATES OF T2.0/30KTS (PGTW), T2.7/39KTS (ADT), AND SATELLITE CONSENSUS (SATCON) OF 44 KTS. TD 04W (CHOI-WAN) IS IN A MARGINAL ENVIRONMENT WITH GOOD WESTWARD AND EQUATORWARD OUTFLOW AND VERY WARM (30-31C) SEA SURFACE TEMPERATURES (SST), OFFSET BY MARGINAL (15- 20KTS) VERTICAL WIND SHEAR. THE CYCLONE IS TRACKING ALONG THE SOUTHWEST PERIPHERY OF THE SUBTROPICAL RIDGE (STR) TO THE EAST- NORTHEAST. 3. FORECAST REASONING. A. THERE IS NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS PROGNOSTIC REASONING MESSAGE. B. TD 04W WILL CONTINUE TO TRACK NORTH-NORTHWESTWARD OVER THE NEXT 24 HOURS UNDER THE STEERING INFLUENCE OF THE STR. THE SYSTEM IS FORECAST TO INTENSIFY TO 35KTS UNDER THE AFOREMENTIONED MARGINAL CONDITIONS AS IT APPROACHES THE RIDGE AXIS. BY TAU 36, TD 04W (CHOI- WAN) WILL BEGIN RAPIDLY DISSIPATING DUE TO LACK OF UPPER LEVEL SUPPORT AND UNFAVORABLE VWS DUE TO CONSISTENT EASTERLY FLOW FROM ANTI-CYCLONIC FEATURE LOCATED OVER SOUTHERN CHINA. BY TAU 48, THE SYSTEM WILL BECOME FULLY DISSIPATED. THE FORECAST TRACK IS LAID IN GOOD AGREEMENT WITH MODEL CONSENSUS FOR THE FIRST 24 HOURS. AFTER TAU 24, THE FORECAST TRACK IS MORE TO THE RIGHT OF FORECAST CONSENSUS TO OFFSET NAVGEM BEING THE EXTREME LEFT OUTLIER WITH A NORTH-NORTHEASTWARD TRACK TOWARD THE WESTERN PORTION OF TAIWAN.// NNNN