WDPN32 PGTW 290300 MSGID/GENADMIN/NAVPACMETOCCEN PEARL HARBOR HI/JTWC// SUBJ/PROGNOSTIC REASONING FOR TYPHOON 13W WARNING NR 12// RMKS/ 1. FOR METEOROLOGISTS. 2. PROGNOSTIC REASONING FOR 290000Z AUG TO 030000Z SEP 2005. A. TYPHOON (TY) 13W (TALIM), LOCATED APPROXIMATELY 490 NM SOUTH- EAST OF OKINAWA, HAS TRACKED WESTWARD AT 13 KNOTS OVER THE PAST SIX HOURS. B. TY 13W IS CURRENTLY BEING STEERED BY A SUBTROPICAL RIDGE SITU- ATED TO THE SOUTHEAST OF JAPAN. AS A TRANSIENT MIDLATITUDE MAJOR SHORTWAVE TROUGH (MSWT) CONTINUES TO MOVE EASTWARD, THE SUBTROPICAL ANTICYCLONE WILL REDEVELOP TO THE WEST AND KEEP TY 13W TRACKING WEST- NORTHWESTWARD. BY APPROXIMATELY TAU 48, A NEW MSWT OVER NORTHEAST CHINA WILL BEGIN TO WEAKEN THE RIDGE AXIS AND ALLOW TY 13W TO BEGIN TRACKING TOWARD NORTHERN TAIWAN. THE AVAILABLE DYNAMIC AIDS CONSIST- ING OF COAMPS, EGRR, GFDN, GFS, JGSM, JTYM, NOGAPS, TCLAPS, AND WBAR ARE IN FAIR AGREEMENT THROUGH TAU 36 AND POOR AGREEMENT THEREAFTER. THIS FORECAST IS BASED ON A CONSENSUS OF ALL AVAILABLE DYNAMIC AIDS WITH LESS EMPHASIS ON EGRR, TCLAPS, AND GFDN. C. TY 13W CONTINUES TO MAINTAIN STRONG EQUATORWARD AND POLEWARD OUTFLOW CHANNELS, HOWEVER THE SYSTEM IS IN AN ENVIRONMENT OF MODERATE VERTICAL WIND SHEAR. THE INTENSITY IS EXPECTED TO INCREASE THROUGH TAU 36, THEN START TO WEAKEN AS TY 13W MOVES CLOSER TO TAIWAN. THE POLEWARD OUTFLOW CHANNEL COULD BECOME DAMPENED THROUGH THE NEXT 48 HOURS DUE TO THE ORIENTATION OF THE RIDGE AXIS OVER THE RYUKYU ISLANDS. D. CURRENT WIND RADII ARE BASED ON A 281258Z AMSU MICROWAVE PASS AND 282100Z SURFACE OBSERVATIONS. FORECAST WIND RADII ARE BASED ON CLIMATOLOGY FOR A LARGE-SIZED SYSTEM. E. DURING THE EXTENDED TAUS, TY 13W IS FORECAST TO MAKE LANDFALL SOUTH OF SHANGHAI, CHINA, NEAR TAU 84. THE SYSTEM WILL QUICKLY WEAKEN AS THE SURFACE INFLOW BECOMES DISRUPTED IN THE WESTERN AND SOUTHERN QUADRANTS. 3. FORECAST TEAM: ALPHA// NNNN