WDPN32 PGTW 101500 MSGID/GENADMIN/NAVPACMETOCCEN PEARL//JTWC// SUBJ/PROGNOSTIC REASONING FOR TYPHOON 20W (NARI) WARNING NR 19// RMKS/ 1. FOR METEOROLOGISTS. 2. PROGNOSTIC REASONING FOR 101200Z4 TO 131200Z7 SEP 01. A. TYPHOON (TY) 20W (NARI), LOCATED APPROXIMATELY 90 NM WEST OF KADENA, HAS DRIFTED EAST-SOUTHEASTWARD AT 6 KNOTS OVER THE PAST SIX HOURS. THE WARNING POSITION IS BASED ON 101130Z6 INFRARED SATELLITE IMAGERY AND RADAR REPORTS. THE WARNING INTENSITY IS BASED ON CURRENT SATELLITE INTENSITY ESTIMATES OF 55 TO 77 KNOTS. ANIMATED INFRARED SATELLITE IMAGERY REVEALS PULSATING CONVECTION ASSOCIATED WITH THE LOW LEVEL CIRCULATION CENTER. B. TY 20W IS CURRENTLY SITUATED WITHIN A WEAKNESS IN THE MID- LEVEL SUBTROPICAL RIDGE RESULTING IN A SLOW EAST-SOUTHEASTWARD TRACK IN THE PAST 6 HOURS. THE SYSTEM IS EXPECTED TO TRACK SOUTHEASTWARD THROUGH 24 HOURS AS IT BEGINS A CYCLONIC LOOP. THE DYNAMIC AIDS OF NOGAPS (NGPS), THE GEOPHYSICAL FLUID DYNAMICS-NAVY (GFDN) MODEL, THE UK-MET OFFICE (EGRR) MODEL, AND GLOBAL SPECTRAL (JGSM) MODELS ARE IN FAIR AGREEMENT WITH THE TRACK. THE GLOBAL MODELS (NGPS, EGRR, AND JGSM) TRACK THE SYSTEM SOUTHEASTWARD THROUGH THE 24 HOUR PERIOD AND THEN TRACK THE SYSTEM MORE WESTWARD THROUGH 72 HOURS. GFDN TRACKS SYSTEM EASTWARD THROUGH THE 24 HOUR PERIOD THEN TRACKS THE SYSTEM NORTH-NORTHWESTWARD. THE OFFICIAL FORECAST IS BASED ON THE NUMERICAL CONSENSUS OF THE FOUR MODELS AND PERSISTENT THROUGH 24 HOURS AND FAVORS THE MORE WESTWARD TRACK OF THE GLOBAL MODELS THROUGH THE 72 HOUR PERIOD. C. TY 20W IS EXPECTED TO MAINTAIN ITS CURRENT INTENSITY THROUGHOUT THE FORECAST PERIOD AS INTENSIFICATION WILL BE HINDERED BY UPWELLING OF COOLER WATER DUE TO THE SLOW MOVEMENT OF THE SYSTEM. D. WIND RADII FOR TY 20W ARE BASED ON CLIMATOLOGY OF A SMALL SIZED SYSTEM. FORECAST TEAM: MAZANY/PARKER/EDBERG// NNNN