WDPN33 PGTW 172100 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TYPHOON 23W (NESAT) WARNING NR 013// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUMMARY: INITIAL POSITION: 18.7N 114.6E INITIAL INTENSITY: 90 KTS GEOGRAPHIC REFERENCE: 217 NM SOUTH OF HONG KONG MOVEMENT PAST 6 HOURS: WEST-SOUTHWESTWARD AT 08 KTS SIGNIFICANT WAVE HEIGHT: 36 FEET SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY SHOWS A FAIRLY SYMMETRICAL MEDIUM-SIZED SYSTEM IN THE SOUTH CHINA SEA WITH COMPACT FEEDER BANDS THAT HAS MAINTAINED ITS OVERALL CONVECTIVE STRUCTURE OVER THE LAST SIX HOURS. A RAGGED PINHOLE EYE HAS BEEN POPPING IN AND OUT. THE INITIAL POSITION IS PLACED WITH MEDIUM CONFIDENCE BASED ON THE INTERMITTENT EYE FEATURE IN THE EIR LOOP. THE INITIAL INTENSITY OF 90KTS IS BASED ON THE CONGRUENT DVORAK ESTIMATES FROM PGTW, KNES, AND RJTD AND REFLECTS THE SUSTAINED 6-HR EIR SIGNATURE. INITIAL WIND RADII BASIS: PERSISTENCE. CURRENT STEERING MECHANISM: DEEP-LAYER SUBTROPICAL RIDGE (STR) TO THE NORTH. AGENCY DVORAK AND AUTOMATED FIXES: PGTW: T5.0 - 90 KTS RJTD: T5.0 - 90 KTS KNES: T5.0 - 90 KTS CIMSS SATCON: 82 KTS AT 171410Z CIMSS ADT: 72 KTS AT 171740Z FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY UNFAVORABLE VWS: 15-20 KTS SST: 28-29 CELSIUS OUTFLOW: MODERATE RADIAL OTHER FACTORS: COLD AIR INTRUSION FROM THE NORTHERN PERIPHERIES ASSOCIATED WITH A COLD NORTHERLY SURGE IN THE NORTHERN SOUTH CHINA SEA. ANALYSIS CONFIDENCE: INITIAL POSITION: MEDIUM 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: TYPHOON NESAT WILL CONTINUE ON ITS CURRENT TRACK THEN FLATTEN TO A MORE WESTWARD TRAJECTORY AFTER TAU 24 UNDER THE STEERING INFLUENCE OF THE STR TO THE NORTH, MAKE LANDFALL JUST SOUTH OF VINH, VIETNAM, SHORTLY AFTER TAU 72 BEFORE TRACKING INLAND. THE MARGINALLY UNFAVORABLE ENVIRONMENT, MAINLY DUE TO THE COLD AIR INTRUSION NEAR THE SURFACE, WILL GRADUALLY ERODE THE SYSTEM DOWN TO 45KTS BY TAU 48. AFTERWARD, INCREASING VWS AND INTERACTION WITH LANDMASS WILL WEAKEN AT A MORE RAPID PACE, LEADING TO DISSIPATION BY TAU 96 AFTER THE SYSTEM CROSSES INTO LAOS. MODEL DISCUSSION: NUMERICAL MODELS ARE IN GOOD AGREEMENT WITH A GRADUAL SPREAD UP TO TAU 48. AFTERWARD, THE MEMBER SPREAD OUT SIGNIFICANTLY TO 320+ NM BY TAU 96 AS THE MODELS HAVE DIFFICULTY TRACKING A MUCH WEAKENED VORTEX. IN VIEW OF THIS, THERE IS OVERALL MEDIUM CONFIDENCE IN THE JTWC TRACK FORECAST UP TO TAU 72, THEN LON CONFIDENCE AFTERWARD. FORECAST CONFIDENCE: TRACK 0 - 72 HR: MEDIUM TRACK 72-120 HR: LOW INTENSITY 0 - 72 HR: MEDIUM INTENSITY 72-120 HR: LOW// NNNN