WDPN31 PGTW 200300 MSGID/GENADMIN/NAVPACMETOCCEN PEARL//JTWC// SUBJ/PROGNOSTIC REASONING FOR TYPHOON 21W (VIPA) WARNING NR 13// RMKS/ 1. FOR METEOROLOGISTS. 2. PROGNOSTIC REASONING FOR 200000Z2 TO 220000Z4 SEP 01. A. TYPHOON (TY) 21W (VIPA), LOCATED APPROXIMATELY 145 NM SOUTH- SOUTHEAST OF TOKYO, HAS TRACKED NORTHEASTWARD AT 12 KNOTS DURING THE PAST SIX HOURS. THE WARNING POSITION IS BASED ON 192330Z8 INFRARED AND VISIBLE SATELLITE IMAGERY AND RADAR IMAGERY. THE WARNING INTENSITY IS BASED ON CURRENT INTENSITY ESTIMATES OF 65 TO 75 KNOTS. ALTHOUGH THE SMALL, IRREGULAR EYE IS NO LONGER EVIDENT DISTINCT CONVECTIVE BANDING FEATURE STILL EXISTS SOUTH THROUGH EAST. THEREFORE, WE HAVE KEPT THE INITIAL INTENSITY AT 70 KNOTS. B. TY 21W HAS MOVED WITHIN THE MID/UPPER WEST-SOUTHWESTERLIES ASSOCIATED WITH A LONG WAVE TROUGH. THE SYSTEM IS EXPECTED TO COMPLETE COMPLEX (MERGING WITH A BAROCLINIC LOW) EXTRA-TROPICAL TRANSITION BY THE END OF THE PERIOD. THE DYNAMICAL MODELS ARE IN AGREEMENT WITH AN EXTRA TROPICAL TRANSITION BY THE 36 HOUR PERIOD. NOGAPS, HOWEVER, REVEALS A SLIGHTLY FASTER TRANSITION AND A DEEPENING TREND AS A BAROCLINIC SYSTEM. OUR FORECAST IS BASED ON THE NUMERICAL CONSENSUS CONSISTING OF FIVE MODELS (NOGAPS, AVN, UKMET-O SPECTRAL, JMA GLOBAL AND TYPHOON AND GFDN). C. TY 21W IS SHOULD SLOWLY WEAKEN AS IT ENCOUNTERS THE MID- LATITUDE WESTERLIES AND COOLER SEA SURFACE TEMPERATURES. NWP INDICATES INTENSIFICATION AS A BAROCLINIC SYSTEM BEYOND THE EXTRA TROPICAL TRANSITION COMPLETION POINT. D. WIND RADII ARE BASED ON SATELLITE IMAGERY AND CLIMATOLOGY FOR A SMALL TROPICAL CYCLONE. FORECAST TEAM: ROBERTS/BALDINGER/HARRISON//