WDPN32 PGTW 110300 
MSGID/GENADMIN/NAVPACMETOCCEN PEARL//JTWC//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 20W (NARI) WARNING 
NR 21//
RMKS/
1. FOR METEOROLOGISTS.
2. PROGNOSTIC REASONING FOR 110000Z2 TO 140000Z5 SEP 01.
   A. TYPHOON (TY) 20W (NARI), LOCATED APPROXIMATELY 68 NM WEST-
SOUTHWEST OF KADENA, HAS DRIFTED EAST-NORTHEASTWARD AT 03 KNOTS OVER 
THE PAST SIX HOURS. THE WARNING POSITION IS BASED ON 102330Z9 
VISIBLE AND INFRARED SATELLITE IMAGERY AND RADAR REPORTS. THE 
WARNING INTENSITY IS BASED ON CURRENT SATELLITE INTENSITY ESTIMATES 
OF 77 TO 90 KNOTS. ENHANCED I/R AND VISIBLE ANIMATION DEPICT THAT A 
(APPROX) 5 NM IRREGULAR EYE HAS DEVELOPED. IMAGERY ALSO REVEALS THAT 
THE DEEP CONVECTION HAS INCREASED OVER THE EASTERN QUADRANT OF THE 
SYSTEM DURING THE PAST 6 HOURS. 
   B. THE POLEWARD ORIENTED MID-LEVEL RIDGE EXTENDING NORTHEASTWARD 
FROM THE SOUTH CHINA SEA SHOULD WEAKEN DURING THE NEXT 12 HOURS 
CURTAILING THE CURRENT EASTWARD DRIFT TOWARD OKINAWA. AFTERWARD, THE 
SUBTROPICAL RIDGE IS FORECAST TO BUILD OVER THE EAST CHINA SEA AS A 
MID-LATITUDE TROUGH LIFTS OUT OF THE SEA OF JAPAN. THE BUILDING MID-
LEVEL RIDGE SHOULD CREATE A STEERING FLOW STRONG ENOUGH TO SEND TY 
20W TO THE WEST. THE DYNAMICAL MODELS (NOGAPS, AVN, JMA GLOBAL AND 
TYPHOON, KMA GLOBAL AND THE UKMET-O GLOBAL SPECTRAL) ARE IN 
AGREEMENT WITH THE AFOREMENTIONED SCENARIO. THE AFWA MESOSCALE (MM5) 
AND COAMPS ARE THE OUTLIERS REVEALING A REVERSE MONSOON TROUGH TRACK 
TO THE NORTHEAST BEHIND TY 19W. THE OFFICIAL FORECAST IS BASED ON 
PERSISTENCE AND THE DYNAMICAL MODEL CONSENSUS AGREEING ON A WESTWARD 
MOTION BY MID PERIOD.  
   C. ALTHOUGH THE SYSTEM HAS REMAINED BENEATH THE UPPER LEVEL 
RIDGE, IT HAS INTENSIFIED AT A NEAR CLIMATOLOGICAL RATE DURING THE 
PAST 24 HOURS. UPWELLING CAUSED BY THE SLOW SPEED OF ADVANCE HAS 
HINDERED A POSSIBLE RAPID DEVELOPMENT TREND. FURTHER INTENSIFICATION 
IS POSSIBLE EARLY IN THE PERIOD BEFORE WE SEE A SLIGHT WEAKENING 
TREND AS THE SYSTEM TRACKS WEST.
   D. WIND RADII FOR TY 20W ARE BASED ON SYNOPTIC DATA AND 
CLIMATOLOGY OF A SMALL SIZED SYSTEM. 
FORECAST TEAM: ROBERTS/BALDINGER/HARRISON//