WDPN33 PGTW 192100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 23W (NESAT) WARNING NR 
021//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 17.4N 108.5E
   INITIAL INTENSITY: 40 KTS
   GEOGRAPHIC REFERENCE: 85 NM NORTH OF DA NANG, VIETNAM
   MOVEMENT PAST 6 HOURS: WEST-NORTHWESTWARD AT 09 KTS
   SIGNIFICANT WAVE HEIGHT: 18 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A
DECAYING SYSTEM WITH A DETERIORATING CONVECTIVE CORE DUE TO STRONG
VERTICAL WIND SHEAR (VWS) AND DRY AIR ENTRAINMENT. AN 191112Z SSMIS
91GHZ MICROWAVE IMAGE REVEALS A FULLY EXPOSED, WELL DEFINED
LOW-LEVEL CIRCULATION CENTER (LLCC) WITH DEEP CONVECTION CONFINED
TO THE NORTHWEST QUADRANT. THE INITIAL POSITION IS PLACED WITH
MEDIUM CONFIDENCE BASED ON AN EARLIER PARTIAL 191436Z ASCAT-C
IMAGE, WHICH SHOWS A DEFINED LOW LEVEL CENTER WITH 35-40 KNOT WINDS
OVER THE NORTHWESTERN PERIPHERY. THE INITIAL INTENSITY OF 40 KTS IS
ASSESSED WITH HIGH CONFIDENCE BASED ON THE PGTW, RJTD DVORAK
ESTIMATES OF T2.0 AND ASCAT DATA. ENVIRONMENTAL CONDITIONS ARE
MARGINAL WITH MODERATE POLEWARD OUTFLOW, WARM (27-28C)
SEA SURFACE TEMPERATURES (SSTS), AND STRONG (20-25KTS) VERTICAL
WIND SHEAR (VWS).

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: T2.0 - 30 KTS
   RJTD: T2.0 - 30 KTS
   CIMSS ADT: 25 KTS AT 191740Z

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: HIGH

3. FORECAST REASONING.

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

FORECAST DISCUSSION: TROPICAL STORM 23W IS FORECAST TO TRACK SLOWLY
WEST-NORTHWEST OVER THE NEXT 12 HOURS ALONG THE SOUTHWEST PERIPHERY
OF THE STR TOWARD VIETNAM WHILE DECAYING IN INTENSITY DUE TO HIGH
VERTICAL WIND SHEAR (VWS) ALONG WITH DRY COOL AIR ENTRAINING INTO
THE SYSTEM. BY TAU 24, TS 23W WILL TRACK SLOWLY TURN AND BEGIN
TRACKING SOUTHWESTWARD. AFTER TAU 24, THE TRACK MOTION IS FORECAST
TO BECOME QUASI-STATIONARY AS THE SYSTEM MAKES LANDFALL OVER
EASTERN VIETNAM. THE SYSTEM WILL THEN DISSIPATE BY TAU 36 OR
PERHAPS EARLIER AS ENVIRONMENTAL CONDITIONS QUICKLY DEGRADE.    


MODEL DISCUSSION: NUMERICAL MODEL GUIDANCE IS IN FAIR AGREEMENT
WITH THE EXCEPTION OF NAVGEM AND SUPPORTS THE JTWC FORECAST TRACK
WITH MEDIUM CONFIDENCE. THE 191200Z GFS (GEFS) ENSEMBLE ALSO SUPPORTS 
THE LATEST TRACK FORECAST AND INDICATES STEADY WEAKENING AND 
DISSIPATION. RELIABLE INTENSITY GUIDANCE SHOWS A STEADY WEAKENING 
TREND AND REMAINS IN GOOD AGREEMENT WITH THE JTWC FORECAST.  

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