WDPN33 PGTW 190300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 23W (NESAT) WARNING NR 
018//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 17.0N 110.9E
   INITIAL INTENSITY: 55 KTS
   GEOGRAPHIC REFERENCE: 161 NM EAST-NORTHEAST OF DA NANG, VIETNAM
   MOVEMENT PAST 6 HOURS: WESTWARD AT 10 KTS
   SIGNIFICANT WAVE HEIGHT: 25 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) SHOWS THE SYSTEM
CONTINUED TO RAPIDLY DECAY AS IT TRACKED TOWARD VIETNAM IN THE
SOUTH CHINA SEA. THE RAGGED LOW LEVEL CIRCULATION HAS BECOME FULLY
EXPOSED AS THE RAPIDLY COLLAPSING CENTRAL CONVECTION IS SHEARED
FURTHER 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 ADJUSTED WITH SURFACE WIND
OBSERVATIONS.

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

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T3.5 - 55 KTS
   RJTD: T3.5 - 55 KTS
   CIMSS SATCON: 52 KTS AT 181841Z
   CIMSS ADT: 49 KTS AT 182040Z

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: 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: TS NESAT WILL CONTINUE ON ITS WESTWARD TRACK
UNDER THE STEERING INFLUENCE OF THE STR, MAKING A FINAL LANDFALL
JUST NORTHWEST OF HUE, VIETNAM, JUST BEFORE TAU 48. 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 48,
POSSIBLY SOONER. 

MODEL DISCUSSION: NUMERICAL MODELS ARE IN OVERALL GOOD AGREEMENT UP
TO TAU 24; 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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