Tropical Storm GAEMI Advisory Sa, 06-10

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 21W (GAEMI) WARNING NR
16//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL STORM 21W (GAEMI), LOCATED APPROXIMATELY 485 NM EAST-
SOUTHEAST OF HUE, VIETNAM, HAS TRACKED WESTWARD AT 09 KNOTS OVER THE
PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY SHOWS THE
LOW LEVEL CIRCULATION CENTER (LLCC) REMAINS FULLY EXPOSED AND HAS
BEEN SLOWLY DETERIORATING OVER THE PAST 12 HOURS. AN EXPANSION OF
THE CENTER AND A SLIGHT ELONGATION OF THE LLCC HAS BEEN OBSERVED
OVER THE PAST SIX HOURS AND IS IN LINE WITH THE 2.5/2.5 DVORAK
INTENSITY ESTIMATES FROM PGTW SUGGESTING THE WEAKENING TREND. THE
TRACK SPEED HAS REMAINED STEADY OVER THE PAST SIX HOURS, UNDER THE
INFLUENCE OF THE BUILDING SUBTROPICAL RIDGE (STR) TO THE NORTH OF
THE SYSTEM. UPPER LEVEL ANALYSIS INDICATES THE SYSTEM REMAINS SOUTH
OF THE STR AXIS, WHICH IS CREATING STRONG EASTERLY FLOW OVER THE
LLCC, LEADING TO MODERATE TO HIGH LEVELS OF VERTICAL WIND SHEAR
(VWS) OVER THE LLCC.
3. FORECAST REASONING.
   A. THERE IS NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE
PREVIOUS PROGNOSTIC REASONING MESSAGE.
   B. TS 21W IS FORECAST TO CONTINUE TRACKING WESTWARD ACROSS THE
SOUTH CHINA SEA TOWARDS VIETNAM UNDER THE STEERING INFLUENCE OF THE
STR AND WILL MAKE LANDFALL SOUTH OF HUE SHORTLY AFTER TAU 36. THE
STORM MOTION IS STILL EXPECTED TO COME INTO PHASE WITH THE UPPER
LEVEL WIND FLOW, CAUSING A SLIGHT DECREASE IN THE VWS AND A BRIEF
PERIOD OF INTENSIFICATION BY TAU 36. AFTER IT MAKES LANDFALL, THE
STORM WILL RAPIDLY WEAKEN AND DISSIPATE BY TAU 72 DUE TO FRICTIONAL
EFFECTS. THE MODEL GUIDANCE IS IN TIGHT AGREEMENT WITH THE DUE
WESTWARD STORM MOTION AND HAS COME INTO BETTER AGREEMENT ON TRACK
SPEEDS. BASED ON THE STEADY SPEEDS AND GOOD MODEL GUIDANCE THERE IS
HIGH CONFIDENCE IN THE CURRENT FORECAST TRACK.//
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