WDPN32 PGTW 211500 MSGID/GENADMIN/NAVPACMETOCCEN PEARL HARBOR HI/JTWC// SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 18W WARNING NR 05// RMKS/ 1. FOR METEOROLOGISTS. 2. PROGNOSTIC REASONING FOR 211200Z TO 261200Z SEP 2005. A. TROPICAL STORM (TS) 18W (SAOLA) LOCATED APPROXIMATELY 420 NM EAST OF IWO JIMA, HAS TRACKED NORTHWESTWARD AT 11 KNOTS OVER THE PAST SIX HOURS B. TS 18W IS TRACKING ALONG THE SOUTHWESTERN PERIPHERY OF THE SUB- TROPICAL RIDGE CENTERED TO THE NORTHEAST. THE CURRENT WEAKNESS IN THE SUBTROPICAL RIDGE NORTHWEST OF THE SYSTEM IS FILLING AS THE TROUGH OFF THE EAST COAST OF JAPAN LIFTS OUT. THE SUBTROPICAL RIDGE IS FORECAST TO BUILD WESTWARD THROUGH TAU 72 AND CONTINUE TO PROVIDE A WESTWARD STEERING INFLUENCE FOR TS 18W. THE DYNAMIC AIDS CONSISTING OF NOGAPS, NCEP GFS, EGRR, GFDN, WBAR, COAMPS, JTYM, JGSM AND AFWA MM5 AND ARE IN FAIR AGREEMENT WITH THIS SCENARIO. THIS FORECAST IS BASED ON A CONSENSUS OF ALL AVAILABLE DYNAMIC AIDS. C. TS 18W IS FORECAST TO INTENSIFY AT AN APPROXIMATELY CLIMATOLOGICAL RATE IN AN ENVIRONMENT OF MODERATE TO LOW VERTICAL WIND SHEAR. THE UPPER LEVEL LOW TO THE WEST OF TS 18W IS FILLING AND IS NO LONGER INHIBITING CONVECTION ON THE WESTERN PERIPHERY OF THE SYSTEM. D. CURRENT WIND RADII ARE BASED ON ANIMATED SATELLITE IMAGERY AND A 210821Z QUIKSCAT PASS. FORECAST WIND RADII ARE BASED ON CLIMATOLOGY FOR AN AVERAGE TO SMALL SIZED SYSTEM. E. IN THE EXTENDED PERIOD, TS 18W IS FORECAST TO TRACK ALONG THE SOUTHERN PERIPHERY OF THE SUBTROPICAL RIDGE AND TURN SLIGHTLY POLEWARD TOWARDS A WEAKNESS IN THE RIDGE IMPARTED BY A TROUGH THAT TRACKS ACROSS NORTHERN JAPAN. SOME DYNAMICAL AIDS FORECAST EASTWARD BUILDING OF A RIDGE OFF OF CHINA THAT PROVIDES SOUTHWESTWARD STEERING INFLUENCE OF TS 18W. THE ANTICIPATED INCREASED INTENSITY OF TS 18W IN THE EXTENDED TAUS AND THE POLEWARD STEERING INFLUENCE OF THE ASSOCIATED BETA GYRE REDUCES THE EXPECTATION OF A SOUTHWESTWARD TURN IN THE EXTENDED TAUS. THE INTENSITY OF THE SYSTEM IS EXPECTED TO PEAK NEAR TAU 96 AS IT COMES UNDER THE INFLUENCE OF GREATER VERTICAL WIND SHEAR. 3. FORECAST TEAM: BRAVO// NNNN