WDPN32 PGTW 280300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 20W (WUTIP) WARNING NR 
06//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL STORM (TS) 20W (WUTIP), LOCATED APPROXIMATELY 543 NM 
EAST-SOUTHEAST OF HANOI, VIETNAM, HAS TRACKED SOUTHWESTWARD AT 06
KNOTS OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE 
IMAGERY (MSI) AND RECENT MICROWAVE IMAGERY INDICATE THAT TS 20W HAS 
INTENSIFIED RAPIDLY OVER THE PAST 24 HOURS (FROM 30 TO 55 KNOTS) AND 
THAT THE SYSTEM HAS STALLED AFTER TURNING SHARPLY SOUTHWESTWARD DUE 
TO WEAKENING OF THE NARROW STEERING RIDGE. ANIMATED INFRARED 
SATELLITE IMAGERY DEPICTS A CENTRAL DENSE OVERCAST FEATURE WITH 
MULTIPLE DEEP CONVECTIVE BANDS WRAPPING TIGHTLY INTO THE LOW-LEVEL 
CIRCULATION CENTER (LLCC). A 272253Z TRMM IMAGE DEPICTS A SMALL, 
WELL-DEFINED MICROWAVE EYE FEATURE WITH IMPROVED CONVECTIVE BANDING 
LOCATED PRIMARILY OVER THE NORTHERN SEMI-CIRCLE AND WESTERN SEMI-
CIRCLE DUE TO WEAK EASTERLY VERTICAL WIND SHEAR. BASED ON THE TRMM 
IMAGE, THERE IS GOOD CONFIDENCE IN THE INITIAL POSITION AND RECENT 
MOTION. ANIMATED WATER VAPOR IMAGERY SHOWS IMPROVED POLEWARD OUTFLOW 
INTO A DEEP SHORTWAVE TROUGH DIGGING INTO EASTERN CHINA. THE INITIAL 
INTENSITY IS ASSESSED AT 55 KNOTS BASED ON DVORAK INTENSITY 
ESTIMATES OF 55 KNOTS FROM KNES AND PGTW. TS 20W IS TRACKING SLOWLY 
ALONG THE SOUTHERN PERIPHERY OF THE SUBTROPICAL STEERING RIDGE (STR) 
POSITIONED TO THE NORTH.  
3. FORECAST REASONING.
   A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS 
PROGNOSTIC REASONING MESSAGE.
   B. TS 20W IS FORECAST TO CONTINUE TRACKING SLOWLY WESTWARD TO 
WEST-SOUTHWESTWARD THROUGH TAU 24 UNDER THE STEERING INFLUENCE OF 
THE WEAK STR. AFTER TAU 24, THE SYSTEM IS EXPECTED TO GRADUALLY 
ACCELERATE WESTWARD AS THE STR REBUILDS (AFTER PASSAGE OF THE 
SHORTWAVE TROUGH). DYNAMIC GUIDANCE DIVERGES WITH SOLUTIONS VARYING 
FROM WEST-SOUTHWESTWARD TO WEST-NORTHWESTWARD. TS 20W IS FORECAST TO 
MAKE LANDFALL OVER VIETNAM NEAR 30/06Z THEN TO DISSIPATE DUE TO LAND 
INTERACTION. TS 20W WILL CONTINUE TO INTENSIFY TO A PEAK INTENSITY 
OF 80 KNOTS PRIOR TO LANDFALL DUE TO GENERALLY FAVORABLE 
CONDITIONS.    
   C. IN THE EXTENDED PERIOD, TS 20W IS FORECAST TO DISSIPATE OVER 
LAND. OVERALL, THERE IS HIGH CONFIDENCE IN THE ENTIRE JTWC FORECAST 
TRACK DESPITE MINOR DIFFERENCES IN THE MODEL SOLUTIONS.//
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