Tropical Storm NESAT Advisory 10月18日

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//
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