WDPN32 PGTW 100300 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 17W (SEVENTEEN) WARNING NR 001// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. TROPICAL DEPRESSION (TD) 17W (SEVENTEEN), LOCATED APPROXIMATELY 358 NM EAST-SOUTHEAST OF DA NANG, VIETNAM, HAS TRACKED WEST-NORTHWESTWARD AT 08 KNOTS (KTS) OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY REVEAL A DEFINED LOW LEVEL CIRCULATION CENTER (LLCC) OBSCURED BY DEEP FLARING CONVECTION OVERHEAD. BASED ON THE MSI AND A 092300Z MHS 89 GHZ MICROWAVE IMAGE WITH CONVECTIVE BANDING BEGINNING TO WRAP INTO THE SYSTEM, THERE IS FAIR CONFIDENCE IN THE INITIAL POSITION. THE INITIAL INTENSITY IS SET AT 25 KTS BASED ON T1.0 (25 KTS) BY PGTW AND KNES ALONG WITH RECENT ASCAT DATA DEPICTING 20-24 KT WINDS TO THE NORTHEAST. TD 17W IS TRANSITING THROUGH AN ENVIRONMENT WHICH IS OVERALL FAVORABLE FOR CONTINUED DEVELOPMENT WITH LOW (5-10 KT ) VERTICAL WIND SHEAR, WARM (29- 30 CELSIUS) SEA SURFACE TEMPERATURES (SST), AND ESTABLISHED EQUATORWARD UPPER-LEVEL OUTFLOW. TD 17W IS TRACKING GENERALLY WEST-NORTHWESTWARD UNDER THE STEERING INFLUENCE OF A SUBTROPICAL RIDGE (STR) POSITIONED TO THE NORTH. 3. FORECAST REASONING. A. THIS IS THE FIRST PROGNOSTIC REASONING MESSAGE AND SETS THE FORECAST PHILOSOPHY. B. TD 17W WILL TRACK GENERALLY WESTWARD THROUGH THE REMAINDER OF THE FORECAST ALONG THE SOUTHERN PERIPHERY OF THE AFOREMENTIONED STR. THROUGH TAU 36, TD 17W WILL STEADILY INTENSIFY TO 45 KTS JUST AFTER LANDFALL SOUTH OF DANANG, VIETNAM. AFTERWARDS, INCREASING VWS AND THE RUGGED TERRAIN OF VIETNAM WILL STEADILY WEAKEN THE SYSTEM UNTIL DISSIPATION BY TAU 72. WITH THE EXCEPTIONS OF NAVGEM WHICH DEPICTS A MORE NORTHWESTWARD TRACK AND THE UKMET ENSEMBLE WHICH DIVERGES AT TAU 24, THE NUMERICAL MODEL GUIDANCE IS IN GOOD AGREEMENT THROUGHOUT THE FORECAST PERIOD WITH ONLY A 50 NM SPREAD AT TAU 48. THE JTWC FORECAST TRACK LIES NEAR THE MULTI-MODEL CONSENSUS AND THE ECMWF MODEL SOLUTION WITH FAIR CONFIDENCE.// NNNN