WDPN32 PGTW 070300 
MSGID/GENADMIN/NAVPACMETOCCEN PEARL//JTWC//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 20W (NARI) WARNING 
NR 05//
RMKS/
1. FOR METEOROLOGISTS.
2. PROGNOSTIC REASONING FOR 070000Z7 TO 100000Z1 SEP 01.
   A. TROPICAL STORM (TS) 20W (NARI), LOCATED APPROXIMATELY 13 NM 
SOUTH OF KADENA, HAS TRACKED EASTWARD AT 07 KNOTS DURING THE PAST 
SIX HOURS. THE WARNING POSITION IS BASED ON 062330Z4 VISIBLE AND 
INFRARED SATELLITE IMAGERY AND RADAR IMAGERY. THE WARNING INTENSITY 
IS BASED ON CURRENT SATELLITE INTENSITY ESTIMATES OF 30 AND 35 KNOTS 
AND SYNOPTIC REPORTS. ANIMATED INFRARED SATELLITE IMAGERY REVEALS A 
SMALL SYSTEM THAT HAS INTENSIFIED SIGNIFICANTLY OVER THE PAST 12 
HOURS.  RADAR IMAGERY IS ALSO DEPICTING A WELL-DEVELOPED LOW LEVEL 
CIRCULATION CENTER.
   B. TS 20W IS TRACKING EASTWARD UNDER THE INFLUENCE OF THE MID-
LEVEL RIDGE TO THE SOUTHEAST. THE NOGAPS, UK-MET OFFICE (EGRR), JMA 
TYPHOON (JTYM), AND JMA GLOBAL (JGSM) MODELS ARE IN GOOD AGREEMENT 
TRACKING THE SYSTEM NORTHEASTWARD THROUGH 12 HOURS. BETWEEN THE 12 
AND 24 HOURS POSITIONS THE MODELS DEPICT A MORE NORTHWARD TRACK AS 
THE RIDGE TO THE EAST STRENGTHENS. AFTER 24 HOURS THE MODELS DEPICT 
A TURN TO THE WEST AS A WEAK RIDGE DEVELOPS NORTH OF THE SYSTEM. THE 
GEOPHYSICAL FLUID DYNAMICS NAVY (GFDN) MODEL IS IN DISAGREEMENT AS 
IT TRACKS THE SYSTEM NORTHWESTWARD THROUGH 48 HOURS AND THEN 
NORTHWARD THROUGH 72 HOURS. THE NON-SELECTIVE CONSENSUS CONSISTS OF 
5 MODELS.  THE OFFICIAL FORECASTS BLENDS PERSISTENCE WITH THE 
SELECTIVE CONSENSUS OF NOGAPS, EGRR, JGSM, AND JTYM.  
   C. TS 20W IS EXPECTED TO DEVELOP AT A CLIMATOLOGICAL RATE IN A 
WEAKNESS OF THE UPPER LEVEL SUBTROPICAL RIDGE.
   D. WIND RADII FOR TS 20W ARE BASED ON CLIMATOLOGY FOR A SMALL 
SIZED TROPICAL CYCLONE.  
FORECAST TEAM: CANTRELL/MAYER/TON//
BT
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