MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TYPHOON 25W (CHAMPI) WARNING NR 24// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. TYPHOON (TY) 25W (CHAMPI), LOCATED APPROXIMATELY 300 NM SOUTH- SOUTHWEST OF IWO TO, JAPAN, HAS TRACKED NORTH-NORTHEASTWARD AT 04 KNOTS OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) SHOWS THE SYSTEM HAS SLIGHTLY WEAKENED EVEN AS IT MAINTAINED A 16-NM EYE SURROUNDED BY AN INTENSE CONVECTIVE CORE. THE INITIAL POSITION IS BASED ON THE EYE IN THE MSI ANIMATION WITH HIGH CONFIDENCE. THE INITIAL INTENSITY OF 115 KNOTS IS BASED ON AN OVERALL ASSESSMENT OF DVORAK ESTIMATES FROM REPORTING AGENCIES AND REFLECTS THE SLIGHT WEAKENING. THE UPPER LEVEL ENVIRONMENT REMAINS MOSTLY FAVORABLE WITH LOW VERTICAL WIND SHEAR (VWS) AND DUAL OUTFLOW; HOWEVER, THE POLEWARD CHANNEL HAS DIMINISHED WITH THE SUBSIDENT EFFECT OF A MID-LATITUDE TROUGH TO THE NORTHWEST. THE CYCLONE IS TRACKING ALONG THE WESTERN PERIPHERY OF A DEEP-LAYERED SUB-TROPICAL RIDGE (STR) TO THE EAST. 3. FORECAST REASONING. A. NO SIGNIFICANT CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS PROGNOSTIC REASONING MESSAGE. B. TY 25W WILL CONTINUE TO TRACK SLOWLY NORTH TO NORTH-NORTHWESTWARD ALONG THE WESTERN PERIPHERY OF THE STR THAT IS BUILDING. AFTER TAU 48, THE SYSTEM WILL ACCELERATE NORTHEASTWARD WHERE ENVIRONMENTAL CONDITIONS WILL 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