MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TYPHOON 25W (CHAMPI) WARNING NR 39// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. TYPHOON (TY) 25W (CHAMPI), LOCATED APPROXIMATELY 136 NM EAST OF IWO TO, JAPAN, HAS TRACKED EAST-NORTHEASTWARD AT 13 KNOTS OVER THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED SATELLITE IMAGERY SHOWS A MOSTLY UNCHANGED CONVECTIVE CORE STRUCTURE THAT IS SURROUNDING A 40NM EYE WHICH SUPPORTS THE INITIAL POSITION WITH HIGH CONFIDENCE. THE SYSTEM CONTINUES TO BE ELONGATED TO THE NORTHEAST AS IT INTERACTS WITH THE MID-LATITUDE WESTERLY FLOW. THE INITIAL INTENSITY IS BASED ON CONGRUENT DVORAK ESTIMATES FROM PGTW AND RJTD. UPPER LEVEL ANALYSIS INDICATES A MARGINAL ENVIRONMENT WITH MODERATE (20-25 KNOT) VERTICAL WIND SHEAR (VWS) BEING OFFSET BY A STRONG POLEWARD OUTFLOW CHANNEL, ENHANCED BY THE MID-LATITUDE ZONAL FLOW. TY 25W IS TRACKING ALONG THE POLEWARD SIDE OF THE SUB-TROPICAL RIDGE (STR) TO THE SOUTHEAST. 3. FORECAST REASONING. A. NO SIGNIFICANT CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS PROGNOSTIC REASONING MESSAGE. B. TY 25W WILL CONTINUE TO TRACK EAST-NORTHEASTWARD ALONG THE NORTHERN PERIPHERY OF THE STR THROUGHOUT THE FORECAST PERIOD. INCREASING VWS AND DECREASING SEA SURFACE TEMPERATURES WILL CONTINUE TO ERODE THE TYPHOON AS IT GAINS LATITUDE. TY CHAMPI WILL BEGIN EXTRA-TROPICAL TRANSITION (ETT) BY TAU 36 AS IT EMBEDS IN THE BAROCLINIC ZONE AND COMPLETES ETT BY THE END OF THE FORECAST PERIOD AS A STRONG COLD CORE LOW. DYNAMIC MODEL GUIDANCE REMAINS IN VERY TIGHT AGREEMENT, LENDING HIGH CONFIDENCE IN THE JTWC FORECAST TRACK.// NNNN NNNN