MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TYPHOON 21W (CHABA) WARNING NR 16// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. TYPHOON (TY) 21W (CHABA), LOCATED APPROXIMATELY 551 NM SOUTH- SOUTHEAST OF KADENA AB, OKINAWA, JAPAN, HAS TRACKED NORTHWESTWARD AT 12 KNOTS OVER THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY SHOWS THE SYSTEM HAS SIGNIFICANTLY CONSOLIDATED AND BECOME MORE SYMMETRICAL, ALBEIT THE CONVECTIVE SIGNATURE HAS VIRTUALLY NOT CHANGED IN THE PAST SIX HOURS. THE INITIAL POSITION IS BASED ON A CENTRAL WARM PIXEL IN THE EIR LOOP AND EXTRAPOLATED FROM CURRENT STORM MOTION WITH FAIR CONFIDENCE. THE INITIAL INTENSITY IS MAINTAINED AT 65 KNOTS BASED ON CONGRUENT AGENCY DVORAK ESTIMATES. TY 21W IS TRACKING IN A FAVORABLE ENVIRONMENT WITH STRONG DIFFLUENCE ALOFT, LOW (5-10 KNOT) VERTICAL WIND SHEAR (VWS), AND VERY WARM (30C) SEA SURFACE TEMPERATURES (SSTS). TY 21W IS TRACKING ALONG THE SOUTHWESTERN PERIPHERY OF THE DEEP-LAYERED SUBTROPICAL RIDGE (STR). 3. FORECAST REASONING. A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS PROGNOSTIC REASONING BULLETIN. B. TY 21W WILL CONTINUE NORTHWESTWARD OVER THE NEXT 36 HOURS TOWARDS OKINAWA. AFTERWARDS, IT WILL ROUND THE STR AXIS AND RECURVE TO THE NORTHEAST. ENVIRONMENTAL CONDITIONS WILL REMAIN FAVORABLE FOR CONTINUED INTENSIFICATION, PEAKING AT 110 KNOTS BY TAU 48 PARTLY DUE TO AN APPROACHING MID-LATITUDE TROUGH THAT WILL ENHANCE POLEWARD OUTFLOW. BY TAU 72, THE CYCLONE WILL APPROACH KYUSHU, JAPAN, AND BEGIN TO WEAKEN MOSTLY DUE TO INCREASING VWS AND COOLING SSTS. DYNAMIC MODEL GUIDANCE REMAINS IN GOOD AGREEMENT THROUGH THIS PORTION OF THE FORECAST PROVIDING HIGH CONFIDENCE. C. IN THE EXTENDED FORECAST, TY CHABA WILL MAKE LANDFALL OVER KYUSHU, JAPAN AND ACCELERATE NORTHEASTWARD. THE SYSTEM WILL DRAG ACROSS THE JAPANESE ISLAND CHAIN AND RAPIDLY ERODE DUE TO LAND INTERACTION, IN ADDITION TO STRONG (30-40 KNOT) VWS. CONCURRENTLY, THE SYSTEM WILL BEGIN EXTRA-TROPICAL TRANSITION (ETT) AND IS EXPECTED TO COMPLETE ETT BY THE END OF THE FORECAST PERIOD AFTER IT TRACKS BACK INTO THE PACIFIC OCEAN EAST OF MISAWA. DYNAMIC MODEL GUIDANCE CONTINUES TO SPREAD BOTH IN TERMS OF SPEED AND DIRECTION AFTER TAU 72. IN VIEW OF THIS, THERE REMAINS LOW CONFIDENCE IN THE EXTENDED PORTION OF THE JTWC TRACK FORECAST.// NNNN NNNN