MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TYPHOON 15W (NAMTHEUN) WARNING NR 10// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. TYPHOON (TY) 15W (NAMTHEUN), LOCATED APPROXIMATELY 281 NM SOUTH OF SASEBO, JAPAN, HAS TRACKED NORTHWARD AT 07 KNOTS OVER THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY SHOWS A COMPACT SYSTEM THAT HAS MAINTAINED DEEP CONVECTIVE SIGNATURE AND A 10-NM EYE. THE INITIAL POSITION IS BASED ON THE EYE FEATURE IN THE EIR LOOP AND ON COMPOSITE RADAR REFLECTIVITY LOOP FROM THE JAPAN METEOROLOGICAL AGENCY WITH GOOD CONFIDENCE. THE INITIAL INTENSITY OF 100 KNOTS IS BASED ON AN OVERALL ASSESSMENT OF OBJECTIVE AND AGENCY FIXES RANGING FROM T5.0 TO T5.5. FAVORABLE ENVIRONMENTAL CONDITIONS WITH SSTS NEAR 29C, HIGH OCEAN HEAT CONTENT, AND STRONG POLEWARD OUTFLOW ARE BEING OFFSET BY INCREASING VERTICAL WIND SHEAR (VWS). THE CYCLONE IS TRACKING ALONG THE WESTERN PERIPHERY OF THE SUBTROPICAL RIDGE (STR) TO THE EAST. 3. FORECAST REASONING. A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS PROGNOSTIC REASONING MESSAGE. B. TY 15W IS FORECAST TO CONTINUE TRACKING NORTHWARD ALONG THE WESTERN PERIPHERY OF THE STR MAKING LANDFALL ALONG THE WESTERN, CENTRAL COAST OF KYUSHU SOUTH OF SASEBO NEAR TAU 30. AFTER TAU 36, THE SYSTEM WILL TURN NORTHEASTWARD AS IT ROUNDS THE STR AXIS, WITH CLOSEST POINT OF APPROACH TO SASEBO AT APPROXIMATELY 26 NM. INCREASING VWS THEN LAND INTERACTION WILL GRADUALLY WEAKEN THE SYSTEM, HOWEVER, IT WILL STILL BE AT TYPHOON INTENSITY AT TAU 36 AS IT APPROACHES SASEBO. RAPID DECAY WILL COMMENCE ONCE THE SYSTEM GOES BACK OVER COLDER WATER (LESS THAN 25C)IN THE SEA OF JAPAN, IN ADDITION TO VERY STRONG VWS (GREATER THAN 40 KNOTS). BY TAU 72, TY 15W WILL BEGIN EXTRA-TROPICAL TRANSITION. C. IN THE EXTENDED TAUS, TY NAMTHEUN WILL ACCELERATE NORTHEASTWARD AND DEEPER INTO THE COLD BAROCLINIC ZONE, BECOMING A COLD-CORE LOW WITH MODERATE GALE-FORCE WINDS BY TAU 96. NUMERIC MODEL GUIDANCE IS IN TIGHT AGREEMENT WITH NAVGEM ON THE EXTREME LEFT OF THE PACK IN THE NEAR TERM THEN CROSSING THE ENVELOPE TO THE EXTREME RIGHT IN THE LONG TERM. THE JTWC TRACK FORECAST HAS BEEN ADJUSTED TO COMPENSATE THIS ERRATIC VORTEX MOTION. OVERALL, CONFIDENCE IN THE JTWC FORECAST REMAINS HIGH.// NNNN NNNN