WDPN31 PGTW 071500 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 12W (YUN-YEUNG) WARNING NR 009// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUMMARY: INITIAL POSITION: 32.0N 137.1E INITIAL INTENSITY: 40 KTS GEOGRAPHIC REFERENCE: 237 NM SOUTHWEST OF YOKOSUKA, JAPAN MOVEMENT PAST 6 HOURS: NORTHWARD AT 11 KTS SIGNIFICANT WAVE HEIGHT: 20 FEET SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: ANIMATED PROXY VISIBLE SATELLITE IMAGERY (PSI) DEPICTS A SYSTEM STRUGGLING TO SURVIVE IN THE FACE OF PERSISTENT, STRONG, SOUTHERLY WIND SHEAR. ANALYSIS OF MULTIPLE BANDS OF SATELLITE IMAGERY, NEARBY UPPER-AIR SOUNDINGS AND PHASE SPACE ANALYSIS SUGGESTS THAT TROPICAL STORM (TS) 12W IS ALREADY IN THE EARLY PHASES OF A PHASE TRANSITION. HIGH RESOLUTION MODEL FIELDS AND RECENT SCATTEROMETER DATA SHOW THE REMNANTS OF A FRONTAL BOUNDARY LYING JUST TO THE NORTHEAST OF THE SYSTEM. INDUCED BY THE STRONG UPPER-LEVEL SOUTHWESTERLY FLOW, THE LOW LEVEL CIRCULATION CENTER (LLCC) IS STARTING TO ROPE OUT ALONG A SOUTHWEST-NORTHEAST DIRECTION ALONG THE OLD BOUNDARY TO THE NORTH. ANIMATED WATER VAPOR IMAGERY SHOWS A WEDGE OF DRY AIR PUNCHING IN FROM THE WEST, RIGHT INTO THE INNER CORE OF THE SYSTEM AND ENHANCED INFRARED (EIR) IMAGERY ALSO SHOWS DEVELOPMENT OF A DELTA RAIN REGION TO THE NORTHEAST OF A ONCE-AGAIN EXPOSED LLCC. THE INITIAL POSITION IS ASSESSED WITH HIGH CONFIDENCE BASED ON THE EXPOSED LLCC AND A 071136Z ASCAT-C PASS WHICH SHOWED THE DEFINED BUT ELONGATING LLCC. THE INITIAL INTENSITY REMAINS SET AT 40 KNOTS WITH HIGH CONFIDENCE BASED ON THE ASCAT-C PASS WHICH SHOWS AN ASYMMETRIC WIND FIELD, WHICH HAS GREATLY EXPANDED TO THE NORTHEAST OVER THE PAST 12 HOURS. THE SYSTEM CONTINUES TO SLOW DOWN AS IT RIDES UP THE WESTERN SIDE OF THE SUBTROPICAL RIDGE (STR) TO THE EAST BUT BEGINS TO RUN INTO A TRANSIENT LOW TO MID-LEVEL ANTICYCLONE PASSING THROUGH THE NORTHERN SEA OF JAPAN. THE ENVIRONMENT HAS STEADILY WORSENED AND IS NOW CONSIDERED UNFAVORABLE, WITH THE SYSTEM FACING VERY HIGH WIND SHEAR, SIGNIFICANT DRY AIR ENTRAINMENT AND THE EARLY PHASES OF EXTRATROPICAL TRANSITION (ETT), WHICH ARE OFFSETTING THE ROBUST POLEWARD OUTFLOW. LASTLY, THE REMNANTS OF 11W (KIROGI) WERE LAST SEEN ABOUT 180NM SOUTH OF THE CURRENT POSITION, MOVING VERY QUICKLY TO THE NORTHEAST. THE REMNANT CIRCULATION WILL BE ABSORBED INTO THE SOUTHEASTERN PERIPHERY OF 12W WITHIN THE NEXT FEW HOURS. INITIAL WIND RADII BASIS: SCATTEROMETER DATA SUPPORTS A LARGE EXPANSION OF THE WIND FIELD IN THE NORTH-NORTHEAST SECTOR. CURRENT STEERING MECHANISM: WESTERN SIDE OF THE SUBTROPICAL RIDGE (STR) TO THE EAST. AGENCY DVORAK AND AUTOMATED FIXES: PGTW: T2.5 - 35 KTS RJTD: T2.0 - 30 KTS RCTP: T2.5 - 35 KTS KNES: T2.5 - 35 KTS CIMSS ADT: 37 KTS AT 071130Z FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: UNFAVORABLE VWS: 30+ KTS SST: 28-29 CELSIUS OUTFLOW: STRONG POLEWARD ANALYSIS CONFIDENCE: INITIAL POSITION: HIGH INITIAL INTENSITY: HIGH INITIAL WIND RADII: HIGH 3. FORECAST REASONING. SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO THE FORECAST FROM THE PREVIOUS WARNING. FORECAST DISCUSSION: TS 12W THE SYSTEM IS NOW TRACKING NORTHWARD ALONG THE NORTH-SOUTH ORIENTED STR TO THE EAST BUT IS SLOWING DOWN AT A RAPID CLIP THIS MORNING, WITH A DEVELOPING ANTICYCLONE TO THE NORTH BLOCKING ITS PATH. THE ANTICYCLONE TO THE NORTH IS TRANSIENT HOWEVER AND WILL HAVE MOVED EAST OF HOKKAIDO BY TAU 24, ALLOWING TS 12W TO RESUME ITS TREK TOWARDS CENTRAL HONSHU. LANDFALL IS EXPECTED TO OCCUR BETWEEN TAU 12 AND TAU 18 IN THE VICINITY OF HAMAMATSU. AS DESCRIBED ABOVE, THE SYSTEM IS ALREADY SHOWING SIGNS OF BEGINNING THE EARLY PHASES OF A TRANSITION TO A SHALLOW, ASYMMETRIC WARM CORE SYSTEM. HOWEVER, WIND SPEEDS ARE LIKELY TO REMAIN WHERE THEY ARE FOR THE TIME BEING, ESPECIALLY AS THE SYSTEM APPROACHES THE COAST AND GETS A BOOST FROM TERRAIN INDUCED FUNNELING EFFECTS. CONVECTION IS HOWEVER, LIKELY TO BE UNABLE TO MAINTAIN ITSELF IN ANY ORGANIZED FASHION FROM NOW THROUGH LANDFALL IN THE FACE OF THE EXTREMELY HIGH WIND SHEAR. AS THE SYSTEM MAKES LANDFALL, IT IS LIKELY TO STRETCH OUT TOWARDS THE NORTHEAST, WITH A SECONDARY AREA OF LOW PRESSURE AND CIRCULATION SPINNING OFF EAST OF THE JAPANESE ALPS AND TRACKING TO THE NORTHEAST ALONG THE EAST COAST OF HONSHU. THE PRIMARY CIRCULATION THE SYSTEM WILL STEADILY WEAKEN AFTER LANDFALL, WITH WHAT REMAINS FOLLOWING AN ERRATIC PATH, LIKELY MAKING THE APPEARANCE OF JUMPING TO A NEW AREA OF LOW PRESSURE OFF THE NORTHERN COAST OF HONSHU BY TAU 36. DISSIPATION AS A TROPICAL CYCLONE IS ANTICIPATED NO LATER THAN TAU 48 BUT POSSIBLY MUCH EARLIER IF THE SYSTEM CANNOT MAKE IT INTACT OVER THE JAPANESE ALPS. WHILE THE SYSTEM IS ALREADY SHOWING SIGNS OF A PHASE TRANSITION, IT IS NOT EXPECTED TO FULLY TRANSITION TO AN EXTRATROPICAL LOW, AS IT WILL REMAIN SOUTH OF THE PRIMARY BAROCLINIC ZONE AND WILL DISSIPATE PRIOR TO MOVING INTO THE PRIMARY BAROCLINIC ZONE. MODEL DISCUSSION: DETERMINISTIC AND ENSEMBLE TRACK GUIDANCE IS IN FAIRLY GOOD AGREEMENT, THOUGH THE CONSENSUS MEAN AND THE GUIDANCE PACKAGE AS A WHOLE CONTINUE TO WALK WESTWARD WITH EACH SUCCESSIVE MODEL RUN. THE GEFS ENSEMBLE MEAN NOW MARKS THE WESTERN EDGE OF THE ENVELOPE, TRACKING THE CENTER OF THE SYSTEM JUST EAST OF KYOTO, WHILE THE ECENS MEAN IS THE EASTERN OUTLIER TAKING THE CENTER THROUGH CENTRAL HONSHU. THE JTWC FORECAST LIES ON THE EASTERN EDGE OF THE ENVELOPE WITH MEDIUM CONFIDENCE, TEMPERED BY THE UNCERTAINTY IN THE ULTIMATE EVOLUTION OF THE LLCC, WHETHER IT SPLITS AND HOW MUCH OF IT REMAINS INTACT TO JUMP OVER THE JAPANESE ALPS. INTENSITY GUIDANCE IS IN GOOD AGREEMENT ON A STEADY INTENSITY THROUGH LANDFALL FOLLOWED BY RAPID WEAKENING, WITH SOME GUIDANCE SUGGESTING A DISSIPATION AS EARLY AS TAU 24, LENDING MEDIUM CONFIDENCE TO THE JTWC FORECAST. FORECAST CONFIDENCE: TRACK 0 - 72 HR: MEDIUM INTENSITY 0 - 72 HR: MEDIUM// NNNN