WDPN31 PGTW 162100 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 09W (CHANTHU) WARNING NR 15// RMKS// 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. TROPICAL STORM 09W (CHANTHU), LOCATED APPROXIMATELY 91 NM NORTHEAST OF YOKOSUKA, JAPAN, HAS TRACKED NORTH-NORTHEASTWARD AT 10 KNOTS OVER THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED SATELLITE IMAGERY AND COMPOSITE RADAR FROM THE JAPAN METEOROLOGICAL AGENCY DEPICT THE LOW-LEVEL CIRCULATION CENTER (LLCC) MOVING PARALLEL TO THE COAST OF JAPAN. FLARING CONVECTION ASSOCIATED WITH THE LLCC IS WEAKENING WITH ENHANCED POLEWARD OUTFLOW AS THE SYSTEM INTERACTS WITH THE MID-LATITUDE FLOW AND BEGINS ITS EXTRATROPICAL TRANSITION. THE INITIAL POSITION IS BASED ON RADAR IMAGERY WITH HIGH CONFIDENCE. THE INITIAL INTENSITY IS BASED ON DVORAK INTENSITY ESTIMATES OF T2.5 FROM PGTW AND RJTD. ALTHOUGH POLEWARD UPPER-LEVEL OUTFLOW IS GOOD, VERTICAL WIND SHEAR IS RAPIDLY INCREASING (25 TO 30 KNOTS) AS TS 09W TRACKS ALONG THE WESTERN PERIPHERY OF A SUBTROPICAL RIDGE (STR) AND TOWARD A MID-LATITUDE TROUGH TO THE NORTHWEST. 3. FORECAST REASONING. A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS PROGNOSTIC REASONING MESSAGE. B. TS 09W IS EXPECTED TO ACCELERATE TOWARD THE NORTH- NORTHEAST AS IT BEGINS ITS EXTRATROPICAL TRANSITION AND BECOMES INCREASINGLY EMBEDDED WITH THE 500 MB FLOW AHEAD OF THE APPROACHING MID-LATITUDE TROUGH. TS 09W IS EXPECTED TO BECOME EXTRATROPICAL IN APPROXIMATELY 24 HOURS. DYNAMIC MODEL GUIDANCE REMAINS IN TIGHT AGREEMENT, LENDING HIGH CONFIDENCE TO THE CURRENT JTWC TRACK FORECAST./=