WDPN32 PGTW 160300 
MSGID/GENADMIN/NAVPACMETOCCEN PEARL//JTWC//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 20W (NARI) WARNING 
NR 41//
RMKS/
1. FOR METEOROLOGISTS.
2. PROGNOSTIC REASONING FOR 160000Z7 TO 190000Z0 SEP 01.
   A. TYPHOON (TY) 20W (NARI), LOCATED APPROXIMATELY 98 NM EAST-
NORTHEAST OF TAIPEI, TAIWAN, HAS DRIFTED WESTWARD AT 3 KNOTS 
DURING THE PAST SIX HOURS. THE WARNING POSITION IS BASED ON 152330Z4 
INFRARED AND VISIBLE SATELLITE IMAGERY ALONG WITH RADAR IMAGERY. THE 
WARNING INTENSITY IS BASED ON SATELLITE CURRENT INTENSITY ESTIMATES 
OF 77 TO 102 KNOTS. VISIBLE ANIMATION DEPICTS A DISTINCT, (APPROX) 
25 NM ROUND EYE. 
   B. MID-LEVEL EQUATORWARD FLOW, GENERATED BY AN EXTENSION OF THE 
SUBTROPICAL RIDGE SITUATED OVER EASTERN CHINA, SHOULD CONTINUE TO 
WEAKEN THROUGH THE PERIOD. CONSEQUENTLY, TY 20W IS FORECAST TO DRIFT 
GENERALLY, WEST-SOUTHWESTWARD TOWARD TAIWAN BEFORE INTERACTING WITH 
THE MOUNTAIN RANGE OF TAIWAN. THE DYNAMICAL AIDS ALL REVEAL A 
SIGNIFICANT REDUCTION IN FORWARD MOTION COMPARED TO THE EARLIER RUNS 
(WEAKENING TREND OF THE RIDGE). IN TERMS OF TRACKER ORIENTATION, 
THERE IS A SPLIT WITH EITHER A MORE WESTWARD TREND BEYOND 36 TAU AND 
REGENERATION OVER THE TAIWAN STRAIT (GFDN, AVN, NOGAPS, UKMET-O) OR, 
DISSIPATION OVER TAIWAN (COAMPS, AFWA MESOSCALE (MM5), 
AND THE JMA GLOBAL AND TYPHOON). OUR FORECAST IS BASED ON 
PERSISTENCE, A BLEND OF THE MENTIONED DYNAMICAL MODELS AND TERRAIN 
EFFECTS LATE IN THE PERIOD.
   C. TY 20W SHOULD REMAIN BENEATH AN EXTENSION OF THE UPPER RIDGE 
AXIS EXTENDING EASTWARD FROM CHINA DURING THE FORECAST PERIOD. 
SHORT TERM INTENSIFICATION IS POSSIBLE BEFORE MAKING LANDFALL OVER 
TAIWAN.     
   D. WIND RADII FOR TY 20W ARE BASED ON SATELLITE IMAGERY AND 
CLIMATOLOGY FOR A SMALL SIZED TROPICAL CYCLONE. 
FORECAST TEAM: ROBERTS/LEEJOICE/BALDINGER/JACOBS/HARRISON//