WDPN31 PGTW 071500 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TYPHOON 16W (CHAN-HOM) WARNING NR 012// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. TYPHOON (TY) 16W (CHAN-HOM), LOCATED APPROXIMATELY 322 NM EAST OF KADENA AB, OKINAWA, HAS TRACKED NORTHWESTWARD AT 10 KNOTS OVER THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED SATELLITE IMAGERY DEPICTS A CONSOLIDATING SYSTEM WITH A RAGGED 30-NM EYE, WHICH SUPPORTS THE INITIAL POSITION AND RECENT TRACK MOTION WITH GOOD CONFIDENCE. A 070901Z WINDSAT 37GHZ MICROWAVE IMAGE INDICATES IMPROVED CONVECTIVE BANDING WRAPPING TIGHTLY INTO A MICROWAVE EYE FEATURE. THE INITIAL 34-KNOT AND 50-KNOT WIND RADII ARE BASED ON A DETAILED ANALYSIS OF THE 071143Z ASCAT-A BULLSEYE IMAGE. THIS IMAGE REFLECTS THE DIFFICULTY IN DETERMINING THE EXTENT OF SYSTEM VERSUS FRONTAL GALE- FORCE WINDS, ESPECIALLY OVER THE NORTHWEST QUADRANT, WHICH ARE MERGED. THE INITIAL INTENSITY IS ASSESSED AT 70 KNOTS BASED ON AN AVERAGE OF PGTW/KNES DVORAK INTENSITY ESTIMATES OF T4.5 (77 KNOTS) AND AN RJTD ESTIMATE OF T4.0 (65 KNOTS). ENVIRONMENTAL CONDITIONS REMAIN FAVORABLE WITH ENHANCED POLEWARD OUTFLOW, GOOD EQUATORWARD OUTFLOW, LOW (5-10 KT) VERTICAL WIND SHEAR (VWS), AND WARM (28-29 CELSIUS) SEA SURFACE TEMPERATURES. THE SYSTEM IS TRACKING ALONG THE SOUTHWESTERN PERIPHERY OF A SUBTROPICAL RIDGE (STR) POSITIONED TO THE NORTHEAST. 3. FORECAST REASONING. A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS PROGNOSTIC REASONING MESSAGE. IMPORTANT NOTE: TY 16W HAS MAINTAINED EXTENSIVE GALE-FORCE WINDS AS LARGE AS 240NM RADIUS. TO FURTHER COMPLICATE THIS SCENARIO, THE SYSTEM IS TRACKING INTO A STRONG BAROCLINIC ZONE WITH ITS OWN TIGHT GRADIENT AS EVIDENCED BY 30 TO 40 KNOT SURFACE WIND REPORTS ACROSS WESTERN JAPAN AND THE RYUKYU ISLANDS. THUS GALE-FORCE WINDS ARE POSSIBLE ALONG AND OUTSIDE THE PERIPHERY OF THE SYSTEM AS IT TRACKS CLOSER TO JAPAN. B. TY 16W IS FORECAST TO TRACK NORTHWESTWARD TO NORTHWARD THROUGH TAU 48 AS IT RECURVES. NUMERICAL MODEL GUIDANCE IS IN BETTER AGREEMENT BUT STILL INDICATES SIGNIFICANT UNCERTAINTY IN THE TIMING AND POINT OF THE RECURVE WITH A 100NM SPREAD IN SOLUTIONS AT TAU 36. AFTER TAU 48, THE SYSTEM WILL ACCELERATE NORTHEASTWARD AS IT BEGINS TO INTERACT WITH THE MIDLATITUDE WESTERLIES. THE UNCERTAINTY IN THE NUMERICAL MODEL SOLUTIONS IS DUE TO THE PRESENCE OF A LARGE BREAK IN THE WESTERN AND EASTERN SUBTROPICAL RIDGES AND THE LACK OF A DYNAMIC MIDLATITUDE SHORTWAVE TROUGH, WHICH WOULD TYPICALLY ACCELERATE THE SYSTEM POLEWARD. IN FACT, THE GLOBAL MODELS DEPICT A ZONAL PATTERN WITH A SHORTWAVE RIDGE PROPAGATING OVER THE KOREAN PENINSULA NEAR TAU 36-48. TY 16W IS FORECAST TO INTENSIFY TO A PEAK INTENSITY OF 80 KNOTS BY TAU 24 UNDER FAVORABLE CONDITIONS. BASED ON THE COMPLEX STEERING PATTERN AND SPREAD IN SOLUTIONS, THERE IS FAIR CONFIDENCE IN THIS PORTION OF THE JTWC FORECAST TRACK. C. AFTER TAU 72, THE SYSTEM WILL ACCELERATE EAST-NORTHEASTWARD ALONG THE SOUTHERN COAST OF JAPAN. DUE TO HIGH (>35 KTS) VWS, TY 16W IS EXPECTED TO WEAKEN STEADILY FOR THE REMAINDER OF THE FORECAST PERIOD TO AN INTENSITY OF 50 KTS BY TAU 96. TY 16W WILL COMPLETE ETT BY TAU 96 AS IT GAINS FRONTAL CHARACTERISTICS. THE JTWC FORECAST TRACK IS POSITIONED ON THE SOUTHERN EDGE OF THE AIDS ENVELOPE CLOSE TO THE ECMWF SOLUTION AND THE MULTI-MODEL CONSENSUS. DUE TO UNCERTAINTY IN THE TRACK AS THE SYSTEM UNDERGOES ETT, THERE IS FAIR CONFIDENCE (MODERATE UNCERTAINTY) IN THE JTWC FORECAST TRACK. THEREFORE, THE JTWC FORECAST TRACK COULD SHIFT CLOSER TO THE KANTO PLAIN.// NNNN