Tropical Storm NESAT Advisory Di, 18.10.

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
NNNN