WDPN31 PGTW 040300
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 04W (CHOI-WAN) WARNING 
NR 022//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL STORM (TS) 04W (CHOI-WAN), LOCATED APPROXIMATELY 324 NM
SOUTH-SOUTHWEST OF TAIPEI, TAIWAN, HAS TRACKED NORTHWESTWARD AT 08 
KNOTS OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE 
IMAGERY (MSI) SHOWS THE BROAD AREA OF CONVECTION ASSOCIATED WITH TS 
04W HAS BECOME TOTALLY OFFSET TO THE SOUTHWEST FROM A FULLY EXPOSED 
LOW LEVEL CIRCULATION CENTER (LLCC). THE INITIAL POSITION IS PLACED 
WITH HIGH CONFIDENCE BASED ON THE AFOREMENTIONED MSI AND THE 032350Z 
PGTW SATELLITE FIX. THE INITIAL INTENSITY OF 35 KTS IS SET WITH GOOD 
CONFIDENCE BASED ON THE OVERALL ASSESSMENT OF DVORAK ESTIMATES OF 
T2.0/30KTS (PGTW), T2.0/30KTS (ADT), AND SATELLITE CONSENSUS 
(SATCON) OF 37KTS AND REFLECTS THE WEAKENING STATE OF THE CYCLONE. 
THE SYSTEM IS IN A MARGINAL ENVIRONMENT WITH GOOD WESTWARD AND 
EQUATORWARD OUTFLOW AND VERY WARM (30-31C) SEA SURFACE TEMPERATURES, 
OFFSET BY MODERATE TO STRONG (20-25KT) VERTICAL WIND SHEAR 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 HAS MADE ITS NORTHEASTWARD TURN AROUND THE AXIS OF THE 
STR AND AFTER TAU 12 WILL DECREASE IN INTENSITY TO 30 KTS DUE TO 
INCREASING VWS AND INTERACTION WITH THE SOUTHERN PORTION OF THE 
CHUNGYANG MOUNTAIN RANGE IN TAIWAN. BY TAU 24, THE SYSTEM WILL 
WEAKEN TO 25 KTS DUE TO HIGH (>25KTS) VWS ASSOCIATED WITH STRONG 
NORTHEASTERLY FLOW FROM A SECONDARY STR ANCHORED OVER SOUTHEASTERN 
CHINA. BY TAU 36, POSSIBLY SOONER, THE SYSTEM WILL BE FULLY 
DISSIPATED AND WILL GET ABSORBED INTO THE MEI-YU FRONTAL BOUNDARY 
APPROACHING FROM THE WEST. NUMERICAL MODELS ARE IN TIGHT AGREEMENT, 
SPREADING TO A MERE 52NM AT TAU 36, LENDING HIGH CONFIDENCE TO THE 
JTWC TRACK FORECAST.//
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