WDPN31 PGTW 071500 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 07W (OMAIS) WARNING NR 13// RMKS// 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. TROPICAL STORM (TS) 07W (OMAIS), LOCATED APPROXIMATELY 400 NM SOUTHEAST OF YOKOSUKA, JAPAN, HAS TRACKED NORTH-NORTHWESTWARD AT 12 KNOTS OVER THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED SATELLITE IMAGERY DEPICTS A BROAD AND ILL-DEFINED LOW LEVEL CIRCULATION CENTER (LLCC) WITH LIMITED CONVECTION ALONG THE EASTERN SEMI-CIRCLE. A 071107Z ASCAT PASS SHOWS A BROAD LLCC SPANNING 60NM WITH 40 TO 45 KNOT WINDS LOCATED APPROXIMATELY 90NM TO THE NORTHEAST. THE ASCAT PASS SUPPORTS THE CURRENT POSITION AND INTENSITY WITH FAIR CONFIDENCE. ENVIRONMENTAL ANALYSIS DEPICTS A MARGINAL TO POOR ENVIRONMENT DUE TO DRY AIR ENTRAINMENT AND SEA SURFACE TEMPERATURES (SSTS) DECREASING BELOW 27 CELSIUS. TS 07W IS TRACKING POLEWARD ALONG THE WESTERN PERIPHERY OF A DEEP-LAYERED SUB- TROPICAL RIDGE (STR) POSITIONED TO THE EAST. 3. FORECAST REASONING. A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS PROGNOSTIC REASONING MESSAGE. B. TS 07W WILL CONTINUE TO TRACK GENERALLY NORTHWESTWARD TO NORTHWARD ALONG THE WESTERN PERIPHERY OF THE STEERING STR OVER THE NEXT 24 HOURS. AFTER TAU 24, IT WILL ROUND THE STR AXIS AND TURN TO THE NORTHEAST. TS OMAIS WILL MAINTAIN ITS CURRENT INTENSITY AS DECENT OUTFLOW AND LOW VERTICAL WIND SHEAR HELP OFFSET THE DRY AIR AND DECREASING SSTS. THE SYSTEM WILL BEGIN EXTRATROPICAL TRANSITION (ETT) NEAR TAU 36, AS IT INTERACTS WITH AN APPROACHING UPPER LEVEL TROUGH. TS 07W WILL COMPLETE ETT BY THE END OF THE FORECAST PERIOD AS IT EMBEDS IN THE MID-LATITUDE WESTERLY FLOW. DYNAMIC MODEL GUIDANCE REMAINS IN VERY TIGHT AGREEMENT, LENDING HIGH CONFIDENCE TO THE JTWC TRACK FORECAST.//