MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TYPHOON 25W (CHAMPI) WARNING NR 20// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. TYPHOON (TY) 25W (CHAMPI), LOCATED APPROXIMATELY 343 NM SOUTH OF IWO TO, JAPAN, HAS TRACKED NORTH-NORTHWESTWARD AT 04 KNOTS OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY SHOWS THE SYSTEM HAS MAINTAINED A 7-NM EYE FEATURE SURROUNDED BY DEEP CONVECTIVE BANDS THAT HAVE WRAPPED TIGHTER INTO THE EYE. THE INITIAL POSITION IS BASED ON THE EYE FEATURE WITH HIGH CONFIDENCE. THE INITIAL INTENSITY OF 100 KNOTS IS BASED ON AN OVERALL ASSESSMENT OF DVORAK ESTIMATES FROM ALL REPORTING AGENCIES AND REFLECTS THE IMPROVED STATE OF THE SYSTEM. UPPER LEVEL ANALYSIS INDICATES TY 25W IS LOCATED IN A FAVORABLE ENVIRONMENT WITH LOW VERTICAL WIND SHEAR (VWS) AND GOOD EQUATORWARD OUTFLOW WITH INCREASED POLEWARD OUTFLOW AS SEEN IN WATER VAPOR IMAGERY. THE CYCLONE IS TRACKING ALONG THE WESTERN PERIPHERY OF A DEEP-LAYERED SUBTROPICAL RIDGE (STR) TO THE EAST-NORTHEAST. 3. FORECAST REASONING. A. NO SIGNIFICANT CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS PROGNOSTIC REASONING MESSAGE. B. TY 25W IS NOW ROUNDING THE WESTERN EDGE OF THE STR AXIS. IT WILL TRACK NORTHWARD UP TO TAU 36 THEN ACCELERATE NORTHEASTWARD ON THE POLEWARD SIDE OF THE STR. AS TY 25W GAINS LATITUDE, ENVIRONMENTAL CONDITIONS WILL BEGIN TO DETERIORATE AS VWS INCREASES AND SEA SURFACE TEMPERATURES DECREASE. C. IN THE EXTENDED FORECAST, TY CHAMPI WILL CONTINUE TO ACCELERATE NORTHEASTWARD AND WEAKEN DUE TO POOR ENVIRONMENTAL CONDITIONS. CONCURRENTLY, THE CYCLONE WILL START TO INTERACT WITH THE BAROCLINIC ZONE AND BEGIN EXTRA-TROPICAL TRANSITION. DYNAMIC MODEL GUIDANCE REMAINS IN TIGHT AGREEMENT THROUGHOUT THE FORECAST PERIOD, LENDING HIGH CONFIDENCE TO THE JTWC FORECAST TRACK.// NNNN NNNN