WDPN31 PGTW 082100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 24W (YINXING) WARNING NR 023//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 18.6N 115.8E
   INITIAL INTENSITY: 100 KTS
   GEOGRAPHIC REFERENCE: 240 NM SOUTH-SOUTHEAST OF HONG KONG
   MOVEMENT PAST 6 HOURS: WESTWARD AT 11 KTS
   SIGNIFICANT WAVE HEIGHT: 48 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY SHOWS THE SYSTEM
REMAINS VERY INTENSE WITH A COMPACT COLD CENTRAL COVER LADEN WITH
OVERSHOOTING CLOUD TOPS THAT HAVE DEEPENED AND A 19-NM EYE THAT HAS
BECOME MORE SYMMETRICAL AND SHARPLY-OUTLINED. THE INITIAL POSITION
IS PLACED WITH HIGH CONFIDENCE BASED ON THE DEFINED EYE IN A LOW
VWS ENVIRONMENT. THE INITIAL INTENSITY IS ALSO ASSESSED WITH HIGH
CONFIDENCE BASED ON EQUALLY ESTIMATED DVORAK VALUES FROM FOUR
REPORTING AGENCIES AND REFLECTS THE 6-HR IMPROVEMENT IN THE EIR
CONVECTIVE SIGNATURE. ANALYSIS INDICATES A FAVORABLE ENVIRONMENT
WITH LOW VWS, WARM SST, AND STRONG POLEWARD OUTFLOW.

INITIAL WIND RADII BASIS: PERSISTENCE.

CURRENT STEERING MECHANISM: DEEP-LAYERED SUBTROPICAL RIDGE (STR) TO
THE NORTH EXTENDING FROM SOUTHERN CHINA THROUGH TAIWAN. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T5.5 - 102 KTS
   RJTD: T5.0 - 90 KTS
   RCTP: T5.5 - 102 KTS
   KNES: T5.5 - 102 KTS
   DEMS: T5.5 - 102 KTS
   CIMSS SATCON: 102 KTS AT 081511Z
   CIMSS ADT: 117 KTS AT 081730Z
   CIMSS DPRNT: 98 KTS AT 081730Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 05-10 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: STRONG POLEWARD

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 YINXING WILL CONTINUE ON ITS CURRENT
WESTWARD TRACK UNDER THE STEERING STR. BY TAU 12, A SECONDARY STR
BUILDING IN FROM THE SOUTHWEST OVER THE INDOCHINA PENINSULA WILL
SLOW DOWN THE FORWARD MOTION OF THE CYCLONE THEN ASSUME STEERING,
DRIVING IT SOUTHWESTWARD TOWARD SOUTHERN VIETNAM AFTER TAU 24. THE
FAVORABLE ENVIRONMENT WILL SUSTAIN THE CURRENT INTENSITY UP TO TAU
12; AFTERWARD, DRY AIR INTRUSION AND COOLER SST WILL GRADUALLY
WEAKEN THE SYSTEM TO 70KTS BY TAU 36. AFTER TAU 36, SIGNIFICANTLY
INCREASING VWS (30+ KTS) AND DRY AIR INTRUSION WILL RAPIDLY ERODE THE 
SYSTEM TO DISSIPATION BY TAU 72 AS IT APPROACHES CENTRAL VIETNAM.    

MODEL DISCUSSION: NUMERICAL MODELS ARE IN FAIRLY GOOD AGREEMENT,
GRADUALLY SPREADING OUT TO 55NM BY TAU 36 THEN TO 168NM BY TAU
72, LENDING OVERALL MEDIUM CONFIDENCE TO THE JTWC TRACK AND
INTENSITY FORECASTS.  

FORECAST CONFIDENCE:
   TRACK 0 - 72 HR: MEDIUM
   INTENSITY 0 - 72 HR: MEDIUM//
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