Tropical Storm CHOI-WAN Advisory Sex, 04-06

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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