WDPN33 PGTW 182100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 23W (NESAT) WARNING NR 017//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 17.2N 111.9E
   INITIAL INTENSITY: 65 KTS
   GEOGRAPHIC REFERENCE: 219 NM EAST-NORTHEAST OF DA NANG, VIETNAM
   MOVEMENT PAST 6 HOURS: WEST-SOUTHWESTWARD AT 08 KTS
   SIGNIFICANT WAVE HEIGHT: 28 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY SHOWS THE SYSTEM
HAS SIGNIFICANTLY DETERIORATED AS IT CONTINUED TO TRACK TOWARD
VIETNAM IN THE SOUTH CHINA SEA. THE LOW LEVEL CIRCULATION HAS
BECOME PARTIALLY EXPOSED AS THE RAPIDLY COLLAPSING CENTRAL
CONVECTION IS SHEARED NORTHWESTWARD. THE INITIAL POSITION IS PLACED
WITH HIGH CONFIDENCE BASED ON THE PARTIALLY EXPOSED LLC. THE
INITIAL INTENSITY IS BASED ON AN OVERALL ASSESSMENT OF AGENCY AND
AUTOMATED DVORAK ESTIMATES AND REFLECTS THE RAPID WEAKENING.

INITIAL WIND RADII BASIS: PERSISTENCE AND SURFACE WIND
OBSERVATIONS.

CURRENT STEERING MECHANISM: SUBTROPICAL RIDGE (STR) TO THE NORTH.

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T4.5 - 77 KTS
   RJTD: T4.0 - 65 KTS
   KNES: T4.5 - 77 KTS
   CIMSS ADT: 61 KTS AT 181430Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: UNFAVORABLE
   VWS: 20-25 KTS
   SST: 27-28 CELSIUS
   OUTFLOW: MODERATE POLEWARD
   OTHER FACTORS: COLD DRY AIR ENTRAINMENT ASSOCIATED WITH THE
NORTHEASTERLY SURGE EVENT IN THE SOUTH CHINA SEA. 

ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   INITIAL INTENSITY: MEDIUM
   INITIAL WIND RADII: MEDIUM

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO
THE FORECAST FROM THE PREVIOUS WARNING.

FORECAST DISCUSSION: TY NESAT WILL TRACK MORE WESTWARD AS THE STR
REORIENTS, MAKING A FINAL LANDFALL JUST NORTH OF HUE, VIETNAM, BEFORE
TAU 72. THE HARSH ENVIRONMENT, CAUSED MOSTLY BY STRONG VERTICAL
WIND SHEAR, COLD DRY AIR INTRUSION NEAR THE SURFACE, AND LAND
INTERACTION WITH THE ISLAND OF HAINAN AND EVENTUALLY WITH VIETNAM,
WILL CONTINUE TO RAPIDLY ERODE THE SYSTEM, LEADING TO DISSIPATION
BY TAU 72, POSSIBLY SOONER. 

MODEL DISCUSSION: NUMERICAL MODELS ARE IN OVERALL GOOD AGREEMENT UP
TO TAU 36; AFTERWARD, THE MEMBERS SIGNIFICANTLY DIVERGE, AN
INDICATION OF DIFFICULTY IN TRACKING A WEAK VORTEX. IN VIEW OF
THIS, THERE IS ONLY MEDIUM CONFIDENCE IN THE JTWC TRACK AND
INTENSITY FORECASTS. 

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