WDPN31 PGTW 181500 MSGID/GENADMIN/NAVPACMETOCCEN PEARL HARBOR HI/JTWC// SUBJ/PROGNOSTIC REASONING FOR TYPHOON 21W WARNING NR 34// RMKS/ 1. FOR METEOROLOGISTS. 2. PROGNOSTIC REASONING FOR 181200Z TO 200000Z OCT 2005. A. TYPHOON (TY) 21W (KIROGI), LOCATED APPROXIMATELY 225 NM SOUTH OF TOKYO, JAPAN, HAS TRACKED NORTHEASTWARD AT 16 KNOTS OVER THE PAST SIX HOURS. THE SYSTEM IS ACCELERATING NORTHEASTWARD AS IT MERGES WITH THE BAROCLINIC ZONE OVER JAPAN. ANIMATED ENHANCED WATER VAPOR IMAGERY DEPICTS A MARKED REDUCTION IN DEEP CONVECTION AND A COMPLETE DISSIPA- TION OF THE EYE FEATURE AS THE SOUTHERN SEMICIRCLE OF THE STORM ERODES. B. THE STORM WILL TRACK RAPIDLY NORTHEASTWARD ALONG THE NORTH- WESTERN PERIPHERY OF THE SUBTROPICAL RIDGE LOCATED TO THE EAST AND IN ADVANCE OF AN APPROACHING MIDLATITUDE TROUGH OVER THE EAST CHINA SEA. WITH THE EXCEPTION OF JGSM, THE AVAILABLE DYNAMIC AIDS CONSISTING OF TCLAPS, NOGAPS, JTYM, NCEP GFS, COAMPS, AFWA MM5, AND GFDN ARE IN FAIR AGREEMENT WITH THE TRACK OF THE SYSTEM THROUGH 36 HOURS. THIS FORECAST IS BASED UPON A CONSENSUS OF ALL AVAILABLE DYNAMIC AIDS, WITH MUCH LESS EMPHASIS PLACED ON JGSM, AN EQUATORWARD OUTLIER. C. THE CONVECTIVE SIGNATURE DEPICTED IN A 180902Z SSM/I PASS AND A 180941Z TRMM PASS INDICATES THAT TY 21W HAS BEGUN EXTRATROPICAL TRANSITION (XT). THE SYSTEM WILL WEAKEN RAPIDLY IN THE HIGH-SHEAR ENVIRONMENT OF THE BAROCLINIC ZONE AND AS IT TRAVERSES MUCH LOWER SEA SURFACE TEMPERATURES. TY 21W IS FORECAST TO COMPLETE XT BY TAU 24. D. CURRENT WIND RADII ARE BASED ON A 180941Z TRMM PASS. FORECAST WIND RADII REFLECT WIND FIELD ASSYMMETRIES DUE TO THE EXTRATROPICAL TRANSITION OF A SMALL- TO AVERAGE-SIZED SYSTEM. 3. FORECAST TEAM: BRAVO// NNNN