WDPN33 PGTW 191500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 23W (NESAT)        
WARNING NR 020//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 17.2N 109.4E
   INITIAL INTENSITY: 40 KTS
   GEOGRAPHIC REFERENCE: 96 NM NORTHEAST OF DA NANG, VIETNAM
   MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 08 KTS
   SIGNIFICANT WAVE HEIGHT: 18 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
TROPICAL STORM (TS) 23W IS EMBEDDED WITHIN A STRATOCUMULUS FIELD
ASSOCIATED WITH A STRONG NORTHEAST SURGE EVENT. SIGNIFICANTLY COOL, 
DRY AIR IS PRESENT ACROSS HAINAN ISLAND AND THE GULF OF TONKIN
WITH DEW POINT TEMPERATURES RANGING FROM 12-18C. CONSEQUENTLY, 
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY REVEALS A RAPIDLY-
DECAYING, FULLY-EXPOSED LOW-LEVEL CIRCULATION WITH NO DEEP 
CONVECTION. THE INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE BASED 
ON THE WELL-DEFINED CENTER EVIDENT IN RECENT CIRA PROXY-VIS IMAGERY. 
AS INDICATED IN A RECENT SCATTEROMETER WINDSPEED IMAGE, THE SYSTEM 
HAS MAINTAINED A SYMMETRIC, SMALL (LESS THAN 60NM DIAMETER) CORE OF 
GALE-FORCE WINDS, WHICH REMAIN SEPARATED FROM THE EXTENSIVE REGION OF 
GALE-FORCE WINDS PERSISTING EAST OF HAINAN ISLAND TO NEAR TAIWAN. THE 
INITIAL INTENSITY OF 40 KTS IS ASSESSED WITH HIGH CONFIDENCE BASED ON 
A BLEND OF THE DVORAK CURRENT INTENSITY ESTIMATES.

INITIAL WIND RADII BASIS: PERSISTENCE 

CURRENT STEERING MECHANISM: LOW- TO MID-LEVEL SUBTROPICAL RIDGE
(STR) POSITIONED TO THE NORTH AND NORTHEAST.

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T2.5 - 35 KTS
   RJTD: T2.5 - 35 KTS
   KNES: T3.0 - 45 KTS
   CIMSS ADT: 25 KTS AT 191140Z

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: MARGINAL
   VWS: 20-25 KTS
   SST: 27-28 CELSIUS
   OUTFLOW: MODERATE POLEWARD
   OTHER FACTORS: DRY AIR ENTRAINMENT

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

3. FORECAST REASONING.

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

FORECAST DISCUSSION: TS 23W WILL TRACK SLOWLY WEST-NORTHWESTWARD TO 
WESTWARD THROUGH TAU 36 AS IT TRACKS ALONG THE SOUTHWEST PERIPHERY OF 
THE STR TOWARD VIETNAM. TS 23W IS FORECAST TO CONTINUE DECAYING 
STEADILY DUE TO PERSISTENT SOUTHERLY VERTICAL WIND SHEAR, DRY AIR 
ENTRAINMENT AND INTERACTION WITH LAND. NEAR TAU 36, THE SYSTEM WILL 
SLOW AND DISSIPATE OVER EASTERN VIETNAM OR JUST EAST OF VIETNAM.

MODEL DISCUSSION: NUMERICAL MODEL GUIDANCE IS IN FAIR AGREEMENT 
SUPPORTING THE JTWC FORECAST TRACK WITH MEDIUM CONFIDENCE. THE 
190600Z GFS (GEFS) ENSEMBLE ALSO SUPPORTS THE LATEST TRACK FORECAST 
AND INDICATES STEADY WEAKENING AND DISSIPATION. RELIABLE INTENSITY 
GUIDANCE REMAINS IN GOOD AGREEMENT WITH A STEADY WEAKENING TREND OVER 
THE NEXT 36 HOURS.  

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