WDPN32 PGTW 201500 MSGID/GENADMIN/NAVPACMETOCCEN PEARL HARBOR HI/JTWC// SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESION 18W WARNING NR 01// RMKS/ 1. FOR METEOROLOGISTS. 2. PROGNOSTIC REASONING FOR 201200Z TO 231200Z SEP 2005. A. TROPICAL DEPRESSION (TD) 18W, LOCATED APPROXIMATELY 500 NM NORTHEAST OF SAIPAN, HAS TRACKED WEST-NORTHWESTWARD AT 06 KNOTS OVER THE PAST SIX HOURS. B. TD 18W IS TRACKING NORTHWESTWARD ALONG THE SOUTHWEST QUADRANT OF THE SUBTROPICAL RIDGE CENTERED TO THE NORTHWEST. A WEAK MID-LATITUDE TROUGH OVER NORTHERN JAPAN AND THE SEA OF JAPAN IS IMPARTING A SLIGHT WEAKNESS IN THE SUBTROPICAL RIDGE TO THE NORTHWEST OF TD 18W. HOWEVER, THE SUBTROPICAL RIDGE POLEWARD OF TD 18W IS FORECAST TO BUILD WESTWARD THROUGH TAU 72 AND CONTINUE TO PROVIDE A WESTWARD STEERING INFLUENCE FOR THE SYSTEM. THE DYNAMIC AIDS CONSISTING OF NOGAPS, EGRR, WBAR AND NCEP GFS ARE IN FAIR AGREEMENT WITH THIS SCENARIO. EGRR FORECASTS LESS WESTWARD BUILDING OF THE STEERING RIDGE POLEWARD OF TD 18W AND THEREFORE A MORE POLEWARD TRACK OF TD 18W. THIS FORECAST IS A CONSENSUS OF ALL AVAILABLE DYNAMIC AIDS. C. TD 18W IS FORECAST TO INTENSIFY AT AN APPROXIMATELY CLIMATOLOGICAL RATE AS IT TRACKS IN AN ENVIRONMENT OF MODERATE VERTICAL WIND SHEAR ALONG THE SOUTHWEST QUADRANT OF THE SUBTROPICAL RIDGE. DEVELOPING UPPER LEVEL LOWS TO THE EAST AND WEST OF TD 18W DO NOT APPEAR TO BE INFLUENCING THE DEVELOPMENT OF TD 18W AT THIS TIME. HOWEVER, THEY WILL BE MONITORED AS MECHANISMS WHICH COULD AFFECT THE INTENSITY OF TD 18W. D. CURRENT AND FORECAST WIND RADII ARE BASED ON CLIMATOLOGY FOR AN AVERAGE TO SMALL SIZED SYSTEM. 3. FORECAST TEAM: BRAVO// NNNN