WDPN32 PGTW 071500 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 23W (CHOI-WAN) WARNING NR 21// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. TROPICAL STORM (TS) 23W (CHOI-WAN), LOCATED APPROXIMATELY 576 NM EAST OF YOKOSUKA, JAPAN, HAS TRACKED NORTHWARD AT 24 KNOTS OVER THE PAST SIX HOURS. ANIMATED ENHANCED IR IMAGERY REVEALS FRAGMENTED CONVECTION LOOSELY WRAPPING ABOUT AN ELONGATED AND ILL-FORMED LLCC. DEEP CONVECTION IS ONLY LOCATED ON THE EASTERN SIDE OF THE SYSTEM AS REFERENCED IN THE 071018Z METOP-B PASS. THE INTENSITY HAS BEEN LOWERED SLIGHTLY TO 60 KNOTS BASED ON THE ASCAT SENSOR PASS, SPECIFICALLY ON THE EASTERN SIDE OF THE SYSTEM. THE CURRENT INTENSITY IS ALSO REFLECTIVE OF THE OVERALL ASSESSMENT OF DVORAK INTENSITY ESTIMATES FROM PGTW, KNES AND RJTD. UPPER LEVEL ANALYSIS SHOWS MODERATE DUAL-CHANNEL OUTFLOW WHICH IS OFFSETTING THE INCREASINGLY HIGH VWS, VISIBLY AFFECTING THE WESTERN PORTION OF THE SYSTEM. THE SYSTEM IS CURRENTLY TRACKING ALONG THE WESTERN PORTION OF A STR IN ADDITION TO INTERACTING WITH A DEEP MID-LATITUDE TROUGH TO THE WEST. 3. FORECAST REASONING. A. NO CHANGE TO FORECAST PHILOSOPHY SINCE THE PREVIOUS PROGNOSTIC REASONING MESSAGE. B. TS CHOI-WAN WILL CONTINUE TO ACCELERATE TO THE NORTH-NORTHWEST THROUGH THE FORECAST PERIOD AS IT CONTINUES TO INTERACT WITH THE BAROCLINIC ZONE PROVIDED BY THE MID-LATITUDE TROUGH APPROACHING FROM THE WEST. AS THE SYSTEM CONTINUES TO TRACK POLEWARD, INCREASED VWS AND DECREASING SSTS VALUES WILL DECAY THE SYSTEM'S INTENSITY THROUGHOUT THE FORECAST PERIOD. EXTRA-TROPICAL TRANSITION WILL CONTINUE TO OCCUR OVER THE NEXT 12 HOURS WITH THE SYSTEM COMPLETING ETT BY TAU 24 AS TS CHOI-WAN GAINS FRONTAL CHARACTERISTICS. EXPECT THE SYSTEM TO MAINTAIN ITS NEAR STORM FORCE AS A FRONTAL SYSTEM IMPACTING THE KURIL ISLAND CHAIN BY TAU 36. DYNAMIC MODEL GUIDANCE REMAINS IN VERY TIGHT AGREEMENT THROUGHOUT THE FORECAST PERIOD LEADING TO HIGH CONFIDENCE IN THE JTWC TRACK FORECAST.// NNNN