WDPN33 PGTW 310300 MSGID/GENADMIN/NAVPACMETOCCEN PEARL//JTWC// SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 18W WARNING NR 09// RMKS/ 1. FOR METEOROLOGISTS. 2. PROGNOSTIC REASONING FOR 310000Z4 AUG 01 TO 020000Z2 SEP 01. A. TROPICAL STORM (TS) 18W (FITOW), LOCATED NORTHWEST OF HAINAN ISLAND IN GULF OF TONKIN, HAS TRACKED NORTHWARD AT 05 KNOTS DURING THE PAST SIX HOURS. THE WARNING POSITION IS BASED ON 302330Z1 INFRARED AND VISIBLE SATELLITE IMAGERY, AND AVAILABLE SYNOPTIC REPORTS. THE WARNING INTENSITY IS BASED ON CURRENT SATELLITE INTENSITY ESTIMATES OF 35 TO 45 KNOTS. B. TS 18W IS TRACKING SLOWLY NORTHWARD UNDER THE INFLUENCE OF THE MID-LEVEL RIDGE SOUTHEAST OF THE CIRCULATION. NOGAPS (NGPS) AND THE GEOPHYSICAL FLUID DYNAMICS NAVY (GFDN) MODEL ARE IN GOOD AGREEMENT TRACKING THE SYSTEM INITIALLY NORTHWESTWARD THEN WESTWARD. THE JMA GLOBAL SPECTRAL (JGSM) MODEL AND THE UK-MET OFFICE (EGRR) MODEL INDICATE AN INITIAL NORTHWARD TRACK WITH A RECURVE TO THE EAST. JTWC ATTRIBUTES THIS TO AN OVERDEVELOPED STEERING RIDGE TO THE SOUTHEAST. DUE TO COMPENSATING ERROR MECHANISMS, THE OFFICIAL FORECAST BLENDS PERSISTENCE WITH THE NUMERICAL CONSENSUS OF NGPS, JGSM, GFDN, AND EGRR THROUGH THE FORECAST PERIOD. C. TS 18W IS EXPECTED TO WEAKEN IN INTENSITY OVER THE NEXT 12 HOURS AS IT MAKES LANDFALL. D. FORECAST WIND RADII ARE BASED ON CLIMATOLOGY FOR AN AVERAGE SIZE SYSTEM. FORECAST TEAM: MAZANY/PARKER/EDBERG//