WDPN31 PGTW 181500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 31W (KIROGI) WARNING 
NR 05//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL STORM (TS) 31W (KIROGI), LOCATED APPROXIMATELY 328 NM 
EAST OF HO CHI MINH CITY, VIETNAM, HAS TRACKED WESTWARD AT 12 KNOTS 
OVER THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED SATELLITE 
IMAGERY DEPICTS A PARTIALLY-EXPOSED LOW-LEVEL CIRCULATION CENTER 
WITH FLARING DEEP CONVECTION DISPLACED OVER THE WESTERN SEMI-CIRCLE. 
AN 181045Z SSMIS 91GHZ IMAGE SHOWS SHALLOW BANDING WRAPPING INTO A 
DEFINED CENTER, HOWEVER, DEEP CONVECTIVE BANDING REMAINS WEAK AND 
FRAGMENTED. THE INITIAL INTENSITY IS ASSESSED AT 35 KNOTS BASED ON 
DVORAK INTENSITY ESTIMATES OF T2.5 (35 KNOTS) FROM RJTD AND PGTW. 
UPPER-LEVEL ANALYSIS INDICATES A MARGINALLY-FAVORABLE ENVIRONMENT 
WITH MODERATE VERTICAL WIND SHEAR OFFSET BY STRONG DIFFLUENT FLOW. 
TS 31W IS TRACKING WESTWARD ALONG THE SOUTHERN PERIPHERY OF THE LOW- 
TO MID-LEVEL SUBTROPICAL RIDGE. 
3. FORECAST REASONING.
   A. THERE IS NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE 
PREVIOUS PROGNOSTIC REASONING MESSAGE.
   B. TS 31W IS FORECAST TO TRACK GENERALLY WESTWARD THROUGH THE 
FORECAST PERIOD, MAKING LANDFALL OVER VIETNAM NEAR TAU 12. THE 
SYSTEM WILL INTENSIFY SLIGHTLY TO A PEAK INTENSITY OF 40 KNOTS BY 
TAU 12 BUT IS EXPECTED TO WEAKEN RAPIDLY AS IT TRACKS INLAND OVER 
MOUNTAINOUS TERRAIN. DYNAMIC GUIDANCE REMAINS IN GOOD AGREEMENT, 
THEREFORE, THERE IS HIGH CONFIDENCE IN THE OFFICIAL JTWC FORECAST 
TRACK.//
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