WDPN33 PGTW 180300 MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI// SUBJ/PROGNOSTIC REASONING FOR TYPHOON 23W (NESAT) WARNING NR 014// RMKS/ 1. FOR METEOROLOGISTS. 2. 6 HOUR SUMMARY AND ANALYSIS. SUMMARY: INITIAL POSITION: 18.2N 113.7E INITIAL INTENSITY: 80 KTS GEOGRAPHIC REFERENCE: 248 NM SOUTH OF HONG KONG MOVEMENT PAST 6 HOURS: WEST-SOUTHWESTWARD AT 10 KTS SIGNIFICANT WAVE HEIGHT: 35 FEET SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) SHOWS A MEDIUM-SIZED SYSTEM IN THE SOUTH CHINA SEA THAT HAS BEGUN TO DETERIORATE AS EVIDENCED BY WARMING CENTRAL CLOUD TOPS AND THE OVERALL STRUCTURE BECOMING ELONGATED AND IRREGULARLY SHAPED. AN INTERMITTENT EYE FEATURE HAS BECOME CLOUD-FILLED. THE INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE BASED ON THE CLOUD-FILLED BUT STILL DISCERNIBLE EYE IN THE MSI LOOP THAT LINED UP WELL WITH A DEFINED MICROWAVE EYE IN THE 172230Z SSMIS 89GHZ COLOR-ENHANCED IMAGE. THE INITIAL INTENSITY OF 80KTS IS BASED ON THE WEAKENING TREND IN THE AGENCY DVORAK ESTIMATES FROM PGTW, KNES, AND RJTD AND REFLECTS THE SUSTAINED 6-HR DETERIORATION. INITIAL WIND RADII BASIS: PERSISTENCE AND SURFACE WIND OBSERVATIONS. 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 ADT: 84 KTS AT 172340Z FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINALLY UNFAVORABLE VWS: 20-25 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: 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: 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 BEFORE 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 IT 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 MEMBERS SPREAD OUT SIGNIFICANTLY TO 340+ 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 LOW 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