WDPN31 PGTW 091500 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 18W (CONSON) WARNING NR 015// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUMMARY: INITIAL POSITION: 16.2N 115.0E INITIAL INTENSITY: 45 KTS GEOGRAPHIC REFERENCE: 360 NM WEST-NORTHWEST OF MANILA, PHILIPPINES MOVEMENT PAST 6 HOURS: WESTWARD AT 20 KTS SIGNIFICANT WAVE HEIGHT: 14 FEET SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A DISORGANIZED SYSTEM THAT HAS IMPROVED SLIGHTLY IN STRUCTURE OVER THE PAST SIX HOURS. THE INITIAL POSITION IS BASED ON UPPER-LEVEL BANDING IN A 091055Z 91GHZ SSMIS IMAGE. THE INITIAL INTENSITY OF 45 KTS IS BASED ON THE MULTI-AGENCY DVORAK INTENSITY ESTIMATES. THE SYSTEM IS CURRENTLY TRACKING WESTWARD IN A MARGINALLY FAVORABLE ENVIRONMENT WITH MODERATE VERTICAL WIND SHEAR, WARM SEA SURFACE TEMPERATURES, AND WEAK RADIAL OUTFLOW ALOFT. INITIAL WIND RADII BASIS: PERSISTENCE CURRENT STEERING MECHANISM: SUBTROPICAL RIDGE TO THE NORTHEAST. AGENCY DVORAK AND AUTOMATED FIXES: PGTW: T3.0 - 45 KTS RJTD: T3.0 - 45 KTS RCTP: T2.0 - 30 KTS KNES: T3.0 - 45 KTS CIMSS ADT: 53 KTS AT 091140Z FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY FAVORABLE VWS: 10-15 KTS SST: 29-30 CELSIUS OUTFLOW: WEAK RADIAL ANALYSIS CONFIDENCE: INITIAL POSITION: MEDIUM INITIAL INTENSITY: MEDIUM INITIAL WIND RADII: LOW 3. FORECAST REASONING. SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO THE FORECAST FROM THE PREVIOUS WARNING. FORECAST DISCUSSION: TROPICAL STORM (TS) 18W IS CURRENTLY TRACKING WESTWARD UNDER THE INFLUENCE OF THE SUBTROPICAL RIDGE TO THE NORTHEAST. AROUND TAU 48, IT WILL TURN MORE WEST-NORTHWESTWARD AS A MID-LATITUDE TROUGH BEGINS TO DEEPEN TO THE NORTH, CREATING A WEAK STEERING ENVIRONMENT. THE SYSTEM IS EXPECTED TO MAKE LANDFALL OVER NORTHERN VIETNAM ROUGHLY 100 NM SOUTH OF HANOI. THE MARGINALLY FAVORABLE ENVIRONMENT WILL ALLOW SLIGHT INTENSIFICATION TO A PEAK OF 70 KTS AROUND TAU 48. AFTERWARD, INCREASING VERTICAL WIND SHEAR AND LAND INTERACTION WITH THE COAST OF VIETNAM WILL WEAKEN THE SYSTEM TO 30 KTS JUST BEFORE LANDFALL AT ABOUT TAU 96. MODEL DISCUSSION: NUMERICAL MODELS ARE IN BETTER AGREEMENT THAN THEY WERE PREVIOUS RUNS. ALL MODELS ARE NOW SHOWING A GENERALLY WESTWARD OR WEST-NORTHWESTWARD TRACK TOWARDS THE COAST OF VIETNAM. HOWEVER, THERE IS STILL A LOT OF UNCERTAINTY ABOUT WHERE THE SYSTEM WILL MAKE LANDFALL, AS CURRENT MODELS SHOW ABOUT A 300 NM SPREAD ACROSS VIETNAM. INTENSITY GUIDANCE IS IN FAIR AGREEMENT, WITH ALL MODELS SHOWING AN INTENSIFICATION PHASE WHICH PEAKS NEAR 70 KTS AROUND TAU 48, FOLLOWED BY A STEADY WEAKENING TREND BEFORE LANDFALL. FORECAST CONFIDENCE: TRACK 0 - 72 HR: HIGH TRACK 72-120 HR: LOW INTENSITY 0 - 72 HR: MEDIUM INTENSITY 72-120 HR: LOW// NNNN