MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 17W (KAMMURI) WARNING NR 15// RMKS/ 1. FOR METEOROLOGISTS. TROPICAL STORM (TS) 17W (KAMMURI), LOCATED APPROXIMATELY 400 NM SOUTH-SOUTHEAST OF YOKOSUKA, JAPAN, HAS TRACKED NORTHWARD AT 11 KNOTS OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL IMAGERY (MSI) DEPICTS A BROAD, PARTIALLY EXPOSED LOW-LEVEL CIRCULATION CENTER (LLCC). THERE IS MODERATE CONFIDENCE IN THE INITIAL POSITION, WHICH IS BASED ON THE MSI LOOP AND A 272306Z SSMIS PARTIAL IMAGE. MICROWAVE IMAGES OVER THE PAST 6 HOURS CONTINUE TO SHOW DEEP CONVECTION ON THE NORTHEASTERN SIDE OF THE SYSTEM ONLY, WITH LIMITED BANDING ABOUT THE LLCC, VISIBLE IN THE MSI. THE INITIAL INTENSITY HAS BEEN LOWERED DUE TO DVORAK CURRENT INTENSITY ESTIMATES FROM ALL AGENCIES. UPPER-LEVEL ANALYSIS INDICATES A MARGINAL ENVIRONMENT CHARACTERIZED BY HIGH (25 TO 50 KNOTS), SOUTHWESTERLY VERTICAL WIND SHEAR REGARDLESS OF THE POLEWARD OUTFLOW DUE TO THE MIDLATITUDE WESTERLIES SLIGHTLY TO THE NORTH. TS 17W IS TRACKING ALONG THE NORTHWESTERN PERIPHERY OF THE SUBTROPICAL RIDGE (STR) POSITIONED TO THE EAST AND SOUTHEAST. 3. FORECAST REASONING. A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS PROGNOSTIC REASONING MESSAGE. B. TS 17W IS FORECAST TO BEGIN EXTRA-TROPICAL TRANSITION (ETT) OVER THE NEXT 12 HOURS AS IT BEGINS TO INTERACT WITH THE MIDLATITUDE WESTERLIES AND THE FRONTAL ZONE, LOCATED JUST NORTH OF THE SYSTEM. AS TS 17W CONTINUES TO ROUND THE STR AXIS, IT WILL FURTHER ACCELERATE TO THE NORTHEAST AND WEAKEN SLIGHTLY AS IT BECOMES EMBEDDED WITHIN THE MIDLATITUDE WESTERLIES. TS KAMMURI WILL COMPLETE ETT BY TAU 48 AS IT IS FORECAST TO GAIN MORE CHARACTERISTICS OF A DEEP COLD-CORE LOW. DYNAMIC MODEL GUIDANCE IS IN GOOD AGREEMENT, THEREFORE, THERE IS HIGH CONFIDENCE IN THE JTWC TRACK, WHICH IS SLIGHTLY FASTER THAN THE MULTI-MODEL CONSENSUS.// NNNN NNNN