WDPN33 PGTW 190300 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 23W (NESAT) WARNING NR 018// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUMMARY: INITIAL POSITION: 17.0N 110.9E INITIAL INTENSITY: 55 KTS GEOGRAPHIC REFERENCE: 161 NM EAST-NORTHEAST OF DA NANG, VIETNAM MOVEMENT PAST 6 HOURS: WESTWARD AT 10 KTS SIGNIFICANT WAVE HEIGHT: 25 FEET SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) SHOWS THE SYSTEM CONTINUED TO RAPIDLY DECAY AS IT TRACKED TOWARD VIETNAM IN THE SOUTH CHINA SEA. THE RAGGED LOW LEVEL CIRCULATION HAS BECOME FULLY EXPOSED AS THE RAPIDLY COLLAPSING CENTRAL CONVECTION IS SHEARED FURTHER NORTHWESTWARD. THE INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE BASED ON THE PARTIALLY EXPOSED LLC. THE INITIAL INTENSITY IS BASED ON AN OVERALL ASSESSMENT OF AGENCY AND AUTOMATED DVORAK ESTIMATES AND REFLECTS THE RAPID WEAKENING. INITIAL WIND RADII BASIS: PERSISTENCE ADJUSTED WITH SURFACE WIND OBSERVATIONS. CURRENT STEERING MECHANISM: SUBTROPICAL RIDGE (STR) TO THE NORTH. AGENCY DVORAK AND AUTOMATED FIXES: PGTW: T3.5 - 55 KTS RJTD: T3.5 - 55 KTS CIMSS SATCON: 52 KTS AT 181841Z CIMSS ADT: 49 KTS AT 182040Z FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: UNFAVORABLE VWS: 20-25 KTS SST: 27-28 CELSIUS OUTFLOW: MODERATE POLEWARD OTHER FACTORS: COLD DRY AIR ENTRAINMENT ASSOCIATED WITH THE NORTHEASTERLY SURGE EVENT IN THE SOUTH CHINA SEA. ANALYSIS CONFIDENCE: INITIAL POSITION: HIGH INITIAL INTENSITY: HIGH INITIAL WIND RADII: MEDIUM 3. FORECAST REASONING. SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO THE FORECAST FROM THE PREVIOUS WARNING. FORECAST DISCUSSION: TS NESAT WILL CONTINUE ON ITS WESTWARD TRACK UNDER THE STEERING INFLUENCE OF THE STR, MAKING A FINAL LANDFALL JUST NORTHWEST OF HUE, VIETNAM, JUST BEFORE TAU 48. THE HARSH ENVIRONMENT, CAUSED MOSTLY BY STRONG VERTICAL WIND SHEAR, COLD DRY AIR INTRUSION NEAR THE SURFACE, AND LAND INTERACTION WITH THE ISLAND OF HAINAN AND EVENTUALLY WITH VIETNAM, WILL CONTINUE TO RAPIDLY ERODE THE SYSTEM, LEADING TO DISSIPATION BY TAU 48, POSSIBLY SOONER. MODEL DISCUSSION: NUMERICAL MODELS ARE IN OVERALL GOOD AGREEMENT UP TO TAU 24; AFTERWARD, THE MEMBERS SIGNIFICANTLY DIVERGE, AN INDICATION OF DIFFICULTY IN TRACKING A WEAK VORTEX. IN VIEW OF THIS, THERE IS ONLY MEDIUM CONFIDENCE IN THE JTWC TRACK AND INTENSITY FORECASTS. FORECAST CONFIDENCE: TRACK 0 - 72 HR: MEDIUM INTENSITY 0 - 72 HR: MEDIUM// NNNN