WDPN31 PGTW 201500 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 04W (LEEPI) WARNING NR 12// RMKS// 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. TROPICAL STORM 04W (LEEPI), LOCATED APPROXIMATELY 282 NM SOUTHWESTWARD OF SASEBO, JAPAN, HAS TRACKED NORTH-NORTHEASTWARD AT 12 KNOTS OVER THE PAST SIX HOURS. ANIMATED INFRARED (IR) SATELLITE IMAGERY CONTINUES TO DEPICT MULTIPLE VORTICES ROTATING AROUND A CENTROID WITH RAPIDLY DECAYING DEEP CONVECTION OVER THE SOUTH QUADRANT. A 201056Z SSMIS IMAGE, HOWEVER, DEPICTS WELL-DEFINED SHALLOW BANDING WRAPPING INTO THE LOW-LEVEL CIRCULATION CENTER (LLCC). THE INITIAL POSITION IS BASED ON THE CENTROID POSITION USING THE AFOREMENTIONED SSMIS IMAGE WITH FAIR CONFIDENCE. THE SYSTEM IS JUST BEGINNING TO INTERACT WEAKLY WITH THE BAROCLINIC ZONE (BAIU BOUNDARY) POSITIONED NEAR CHEJU ISLAND. THE INITIAL INTENSITY IS ASSESSED AT 35 KNOTS, SLIGHTLY HIGHER THAN DVORAK CURRENT INTENSITY ESTIMATES, BASED ON THE WELL-DEFINED STRUCTURE, RECENT SCATTEROMETER DATA AND A SATCON ESTIMATE OF 40 KNOTS. TS 04W IS LOCATED WITHIN AN UNFAVORABLE ENVIRONMENT CHARACTERIZED BY MODERATE VWS AND WEAK INTERACTION WITH THE BAIU BOUNDARY. SEA SURFACE TEMPERATURES REMAIN MARGINALLY FAVORABLE AT 26 TO 27 DEGREES CELSIUS. 3. FORECAST REASONING. A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS PROGNOSTIC REASONING MESSAGE. B. TS 04W IS FORECAST TO ROUND THE SUBTROPICAL RIDGE AXIS WITHIN THE NEXT 12 HOURS THEN ACCELERATE EASTWARD AS IT BEGINS TO ENCOUNTER MIDLATITUDE WESTERLY FLOW. THE SYSTEM WILL BEGIN EXTRA-TROPICAL TRANSITION (ETT) BY TAU 12 THEN COMPLETE ETT BY TAU 36 AS IT TRANSITIONS INTO A COLD-CORE SYSTEM. DYNAMIC MODEL GUIDANCE REMAINS IN TIGHT AGREEMENT, THEREFORE, THERE IS HIGH CONFIDENCE IN THE JTWC FORECAST TRACK. TS 04W WILL GRADUALLY WEAKEN AS IT INTERACTS WITH LAND AFTER TAU 12 AND ENCOUNTERS STRONG VWS BUT IS EXPECTED TO MAINTAIN TROPICAL DEPRESSION STRENGTH THROUGH THE REMAINDER OF THE FORECAST PERIOD.// NNNN