Tropical Storm KOGUMA Advisory Sat Jun 12

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 05W (KOGUMA)
WARNING NR 003//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
    12JUN21. TROPICAL STORM (TS) 05W (KOGUMA), LOCATED APPROXIMATELY
99 NM SOUTHEAST OF HANOI, VIETNAM, HAS TRACKED NORTHWESTWARD AT 17 KNOTS
OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI)
SHOWS THE SYSTEM HAS EXPANDED AND DEEPENED AS IT ACCELERATED ACROSS THE
GULF OF TONKIN EVEN AS THE ASSOCIATED CONVECTION REMAINED SHEARED
WESTWARD AND SOUTHWESTWARD OF THE LOW LEVEL CIRCULATION THAT HAS BECOME
OBSCURED. THE INITIAL POSITION AND INTENSITY OF 35KTS ARE ASSESSED WITH
FAIR CONFIDENCE BASED ON CONCENTRIC PGTW/RJTD DVORAK FIXES OF T2.5/35KTS,
SUPPORTED BY COASTAL AND OFFSHORE SURFACE OBSERVATIONS, AND REFLECTS THE
IMPROVED STATE. THE CYCLONE IS IN A MARGINAL ENVIRONMENT WITH GOOD
WESTWARD AND EQUATORWARD OUTFLOW AND VERY WARM (30-31C) SST OFFSET BY
MODERATE (15-20KTS) VERTICAL WIND SHEAR (VWS). TS 05W IS TRACKING ALONG
THE SOUTHWESTERN PERIPHERY OF THE SUBTROPICAL RIDGE (STR) TO THE EAST-
NORTHEAST.
3. FORECAST REASONING.
   A. THERE IS NO SIGNIFICANT CHANGE TO THE FORECAST PHILOSOPHY FROM THE
PREVIOUS PROGNOSTIC REASONING BULLETIN.
   B. TS KOGUMA WILL CONTINUE ON ITS CURRENT TRACK UNDER THE STR, MAKE
LANDFALL OVER NORTHERN VIETNAM AROUND TAU 06, THEN TRACK INLAND INTO THE
RUGGED VIETNAMESE TERRAIN. THE ROBUST OUTFLOW AND THE WARM SST IN THE
GULF WILL OFFSET THE VWS AND MAY FUEL SLIGHT INTENSIFICATION PRIOR TO
LANDFALL. AFTERWARD, LAND INTERACTION WITH THE RUGGED TERRAIN WILL RESULT
IN A RAPID DECAY LEADING TO DISSIPATION BY TAU 24 AFTER IT PASSES JUST
SOUTH OF HANOI. NUMERICAL MODELS ARE IN FAIR AGREEMENT WITH EVEN AND
GRADUAL SPREADING TO 40NM AT TAU 12; AFTERWARD, ERRATIC DISPERSION AS
THEY LOSE THE VORTEX OVER LAND. IN VIEW OF THIS, THERE IS FAIR CONFIDENCE
IN THE JTWC TRACK FORECAST.//
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