WDPN32 PGTW 111500 
MSGID/GENADMIN/NAVPACMETOCCEN PEARL//JTWC//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 20W (NARI) WARNING 
NR 23//
RMKS/
1. FOR METEOROLOGISTS.
2. PROGNOSTIC REASONING FOR 111200Z5 TO 141200Z8 SEP 01.
   A. TYPHOON (TY) 20W (NARI), LOCATED APPROXIMATELY 35 NM WEST OF 
KADENA, HAS REMAINED QUASISTATIONARY DURING THE PAST SIX HOURS. THE 
WARNING POSITION IS BASED ON 111130Z7 INFRARED SATELLITE IMAGERY AND 
RADAR REPORTS. THE WARNING INTENSITY IS BASED ON CURRENT SATELLITE 
INTENSITY ESTIMATES OF 102 TO 115 KNOTS. ANIMATED INFRARED SATELLITE 
IMAGERY INDICATES THAT DEEP CONVECTION HAS WEAKENED SLIGHTLY DURING 
THE PAST SIX HOURS. 
   B. THE POLEWARD ORIENTED MID-LEVEL RIDGE EXTENDING NORTHEASTWARD 
FROM THE SOUTH CHINA SEA APPEARS TO HAVE WEAKENED AND HALTED THE 
EASTWARD MOVEMENT OF TY 20W. THE SYSTEM REMAINS IN A WEAK STEERING 
REGIME BETWEEN A PERIPHERAL RIDGE TO THE EAST AND A BUILDING RIDGE 
TO THE NORTH. THIS BUILDING MID-LEVEL RIDGE SHOULD CREATE A STEERING 
FLOW STRONG ENOUGH TO SEND TY 20W TO THE WEST BY THE 24 HOUR POINT. 
THE DYNAMICAL MODELS ARE CLUSTERED IN TWO DISTINCT GROUPS. THE UKMET 
GLOBAL MODEL (EGRR), GFDN, COAMPS, AND TO SOME EXTENT THE AFWA MM5 
MODELS TRACK TY 20W SLOWLY NORTHWARD THROUGH THE FORECAST PERIOD. 
THE JAPANESE GLOBAL (JGSM) AND TYPHOON (JTYM) MODELS, AND NOGAPS 
TRACK TY 20W WESTWARD. THE KEY ELEMENT IS A BUILDING RIDGE BLOCKING 
20W TO THE NORTH AND FORCING A WESTWARD MOVEMENT. OUR FORECAST IS 
BASED ON A DYNAMICAL MODEL CONSENSUS BUT FAVORS THE WESTWARD MOTION 
BY MID PERIOD.
   C. THE RECENT INTENSIFICATION IS EXPECTED TO BE NEAR AN END AND 
THE UPWELLING CAUSED BY THE SLOW SPEED OF ADVANCE SHOULD HINDER 
FURTHER DEVELOPMENT. THE SYSTEM IS EXPECTED TO SLOWLY WEAKEN 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: SMITH/MAYER/TON//
BT
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