MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TYPHOON 23W (CHOI-WAN) WARNING NR 18// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. TYPHOON (TY) 23W (CHOI-WAN), LOCATED APPROXIMATELY 222 NM NORTHWEST OF MINAMI TORI SHIMA, HAS TRACKED NORTHWARD AT 14 KNOTS OVER THE PAST SIX HOURS. ANIMATED ENHANCED IR IMAGERY INDICATES A SLIGHT IMPROVEMENT IN CONVECTIVE ORGANIZATION WITH DEEP CONVECTIVE BANDING WRAPPING INTO A BROAD LOW-LEVEL CIRCULATION CENTER. A 061711Z SSMI IMAGE REFLECTS THE BROAD NATURE OF THE SYSTEM AND SHOWS FRAGMENTED DEEP CONVECTION WRAPPING INTO AN ELONGATED, APPROXIMATELY 160-NM EYEWALL-LIKE FEATURE. THE 061711Z SSMI 37GHZ IMAGE SHOWS AN ELONGATED MICROWAVE EYE FEATURE, WHICH SUPPORTS THE CURRENT POSITION WITH FAIR CONFIDENCE. THE CURRENT INTENSITY REMAINS ASSESSED AT 70 KNOTS BASED ON DVORAK INTENSITY ESTIMATES RANGING FROM 65 TO 77 KNOTS. UPPER-LEVEL ANALYSIS DEPICTS A VIGOROUS POLEWARD OUTFLOW CHANNEL ASSOCIATED WITH A DEEP TROUGH ENTRENCHED SOUTH OF JAPAN. TY 23W IS CURRENTLY TRACKING ALONG THE WESTERN PERIPHERY OF A DEEP, POLEWARD-ORIENTED STR. 3. FORECAST REASONING. A. NO CHANGE TO FORECAST PHILOSOPHY SINCE THE PREVIOUS PROGNOSTIC REASONING MESSAGE. WIND RADII HAVE BEEN ADJUSTED SLIGHTLY BASED ON RECENT SCATTEROMETRY DATA, WHICH CONTINUES TO SHOW AN EXPANSIVE REGION OF GALE-FORCE WINDS ESPECIALLY OVER THE NORTHERN SEMI-CIRCLE. B. TY CHOI-WAN WILL CONTINUE TO TRACK POLEWARD THROUGH THE FORECAST PERIOD. TY 23W MAY INTENSIFY SLIGHTLY THROUGH TAU 12 DUE TO FAVORABLE POLEWARD OUTFLOW. BY TAU 12, TY 23W IS FORECAST TO BEGIN EXTRA-TROPICAL TRANSITION (ETT) AS IT BEGINS TO INTERACT WITH THE BAROCLINIC ZONE, ENCOUNTERS INCREASING VERTICAL WIND SHEAR AND TRACKS OVER COOLER SST. TY 23W WILL COMPLETE ETT BY TAU 36 AS IT GAINS FRONTAL CHARACTERISTICS AND BECOMES EMBEDDED WITHIN THE MIDLATITUDE WESTERLIES. THE SYSTEM IS EXPECTED TO MAINTAIN STORM FORCE WINDS AND EXPANSIVE GALE-FORCE WINDS, WHICH COULD ENCROACH ON THE COASTAL REGIONS OF NORTHERN JAPAN. DYNAMIC MODEL GUIDANCE REMAINS IN VERY TIGHT AGREEMENT THROUGHOUT THE FORECAST PERIOD LEADING TO HIGH CONFIDENCE IN THE JTWC TRACK FORECAST.// NNNN NNNN