WDPN31 PGTW 041500
MSGID/GENADMIN/NAVPACMETOCCEN PEARL//JTWC//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 12W (MAN-YI) WARNING 
NR 12// 
1. FOR METEOROLOGISTS.
2. PROGNOSTIC REASONING FOR 041200Z7 TO 071200Z0 AUG 01.
   A. TYPHOON (TY) 12W (MAN-YI) LOCATED APPROXIMATELY 200 NM 
SOUTHEAST OF IWO JIMA, HAS TRACKED NORTH-NORTHWESTWARD AT 14 KNOTS 
DURING THE PAST SIX HOURS. THE WARNING POSITION IS BASED ON 041130Z9 
INFRARED SATELLITE IMAGERY. THE WARNING INTENSITY IS BASED ON 
CURRENT SATELLITE INTENSITY ESTIMATES OF 115 TO 127 KNOTS. ENHANCED 
INFRARED ANIMATION DEPICTS A WELL DEFINED PRIMARY BANDING FEATURE 
WRAPPING IN TOWARD THE VORTEX CENTER FROM THE SOUTHWEST. THEREFORE, 
THE INTENSITY IS BUMPED UP SLIGHTLY FROM THE PREVIOUS WARNING.   
   B. A BAROCLINIC SYSTEM MOVING OFF OF THE NORTHERN COAST OF JAPAN 
SHOULD WEAKEN THE MID-LEVEL HIGH HEIGHT CENTER, SITUATED EAST OF IWO 
JIMA, JUST ENOUGH TO CREATE A NORTH-NORTHEASTWARD STEERING INFLUENCE 
BY THE 36 HOUR PERIOD. THE GEOPHYSICAL FLUID DYNAMICS-NAVY (GFDN), 
UKMET GLOBAL GRID-POINT (EGRR), AND JMA GLOBAL (JGSM) AND REGIONAL 
TYPHOON (JTYM) MODELS, AS WELL AS, THE COAMPS, THE NCEP AVN RUN, AND 
THE AFWA (MM5) MESOSCALE MODELS, ARE IN GOOD AGREEMENT. NOGAPS, 
HOWEVER, CONTINUES TO SHOW A SIGNIFICANT BIAS TO THE WEST. IT 
APPEARS THAT THE BIAS IS CAUSED BY SUBTLE MERGING OF THE TC WITH THE 
MONSOON TROUGH REFLECTION IN THE LOW/MID LEVELS. THE SELECTIVE 
CONSENSUS (SCON) CONSISTS OF FOUR MODELS: GFDN, EGRR, JGSM, AND 
JTYM. THE OFFICIAL FORECAST IS A BLEND OF PERSISTENCE AND THE 
AFOREMENTIONED CLUSTER.
   C. NWP IS IN RELATIVE AGREEMENT WITH A MAXIMUM INTENSITY AROUND 
THE 12 HOUR PERIOD, HOWEVER, PEAK INTENSITY IS ANYWHERE FROM 90 TO 
120 KNOTS. ALSO, SIGNIFICANT WEAKENING IS NOT REVEALED UNTIL THE 72 
HOUR POINT WITH THE SYSTEM BEGINS TO MOVE NORTH OF THE UPPER-LEVEL 
RIDGE. THEREFORE, THE FORECAST INTENSITY WILL FOLLOW THE GUIDANCE, 
PEAKING AT 6.5 (125 KTS) AT THE 12 HOUR TIMEFRAME BEFORE REFLECTING 
A SLOW WEAKENING TREND. 
   D. WIND RADII ARE BASED ON MICROWAVE IMAGERY AND CLIMATOLOGY FOR 
AN AVERAGE SIZE SYSTEM.
   E. THE JTWC WEBSITE HAS CHANGED TO: 
HTTPS://WWW.NPMOC.NAVY.MIL/JTWC.HTML. THIS CHANGE IS FOR SECURITY 
REASONS ONLY. THE CONTENT OF THE WEBSITE HAS NOT CHANGED.//
FORECAST TEAM: ROBERTS/BALDINGER/HARRISON//