Tropical Storm GAEMI Advisory Fri Oct 05

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 21W (GAEMI) WARNING NR
15//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL STORM (TS) 21W (GAEMI), LOCATED APPROXIMATELY 520 NM EAST
OF HUE, VIETNAM, HAS TRACKED WESTWARD AT 08 KNOTS OVER THE PAST SIX
HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) SHOWS THE
LOW LEVEL CIRCULATION CENTER (LLCC) REMAINS FULLY EXPOSED, WITH DEEP
CONVECTION BEING SHEARED TO THE WEST. HOWEVER, THE CENTRAL CONVECTION
HAS DEEPENED AND ITS DISPLACEMENT FROM THE LLCC HAS DECREASED OVER
THE PAST SIX HOURS. THE INITIAL INTENSITY IS BASED ON THE MSI
ANIMATION WITH HIGH CONFIDENCE. THE INITIAL INTENSITY IS AVERAGED
FROM DVORAK ESTIMATES OF 35 TO 45 KNOTS FROM PGTW, KNES, AND RJTD.
UPPER LEVEL ANALYSIS INDICATES THE SYSTEM IS 08 DEGREES SOUTH OF THE
RIDGE AXIS IN AN AREA OF MODERATE (15-20 KNOT) VERTICAL WIND SHEAR
(VWS). THE CYCLONE IS TRACKING ALONG THE SOUTHERN PERIPHERY OF A
BUILDING SUBTROPICAL RIDGE (STR) TO THE NORTH.
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. WITH
THE STORM MOTION NOW IN-PHASE WITH THE UPPER LEVEL WIND FLOW, THE VWS
WILL BE MITIGATED, ALLOWING TS 21W TO INTENSIFY THROUGH TAU 24.
HOWEVER, THE INTENSIFICATION WILL BE TEMPERED BY UPPER LEVEL
SUBSIDENCE FROM THE STR. 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 BUT THERE ARE SIGNIFICANT DIFFERENCES IN THE TRACK SPEEDS. FOR
THIS REASON, THERE IS LOW CONFIDENCE IN THE TRACK FORECAST.    //
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