WDPN31 PGTW 310300 1. FOR METEOROLOGISTS. 2. PROGNOSTIC REASONING FOR 310000Z4 AUG 02 TO 030000Z3 SEP 02. A. TYPHOON (TY) 21W (RUSA), LOCATED APPROXIMATELY 160 NM SOUTH- SOUTHWEST OF PUSAN, HAS TRACKED NORTHWARD AT 11 KNOTS DURING THE PAST 6 HOURS. THE WARNING POSITION IS BASED ON 302330Z1 VISIBLE AND ENHANCED INFRARED SATELLITE IMAGERY. THE WARNING INTENSITY IS BASED ON SATELLITE CURRENT INTENSITY ESTIMATES OF 75 KNOTS AND WEAKENING DEEP CONVECTION. WATER VAPOR ANIMATION DEPICTS STRONG INTERACTION WITH A MID-LAT SHORTWAVE TROUGH PASSING OVER THE SYSTEM. EXTRATROPICAL TRANSITION IS NEARING THE MID-POINT. B. THE MAJOR SHORT WAVE TROUGH IS NOW EXTENDING SOUTHWARD OVER THE YELLOW SEA AND INFLUENCING THE MOTION OF TY 21W. THE POLEWARD TRACK IS FORECAST TO SHIFT TO THE NORTHEAST AS INCREASING WESTERLIES INFLUENCE THE TRACK. THE JMA GLOBAL AND TYPHOON REGIONAL, THE AVN RUN, UKMET GLOBAL, NOGAPS, THE AFWA MESOSCALE (MM5), AND COAMPS ARE IN GOOD AGREEMENT WITH A POLEWARD TRACK OVER THE KOREAN PENINSULA. AFTERWARD, AS THE SYSTEM COMPLETES XT TRANSITION, NWP INDICATES A NORTHEASTWARD TRACK ABOVE THE RIDGE INTO THE SEA OF JAPAN. OUR FORECAST IS BASED ON A BLEND OF AVAILABLE MODELS. C. A WEAKENING TREND IS FORECAST IN RESPONSE TO BAROCLINIC INTERACTION AND TERRAIN EFFECTS. D. INITIAL WIND RADII ARE BASED ON SYNOPTIC DATA. FORECAST WIND RADII ARE BASED ON CLIMATOLOGY FOR A LARGE-SIZED SYSTEM. FORECAST TEAM: SMITH/PIVIN/LAM/KUMAGA/STATEN// NNNN