Tropical Storm DOKSURI Advisory 9月14日

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 21W (DOKSURI)
WARNING NR 09//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL STORM 21W (DOKSURI), LOCATED APPROXIMATELY 295 NM EAST
OF DA NANG, VIETNAM, HAS TRACKED WESTWARD AT 11 KNOTS OVER THE PAST
SIX HOURS.  ANIMATED ENHANCED INFRARED SATELLITE IMAGERY SHOWS STRONG
CONVECTION SOUTH OF THE LOW LEVEL CIRCULATION CENTER (LLCC). THE
INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE BASED ON 131800Z
INFRARED IMAGERY. THE INITIAL INTENSITY OF 60 KNOTS IS BASED ON
EXTRAPOLATION OF 131311Z ASCAT PASS AND SUBJECTIVE DVORAK CURRENT
INTENSITY ESTIMATES OF T3.5 (55 KNOTS) AND T4.0 (65 KNOTS) FROM PGTW
AND KNES RESPECTIVELY.  ANALYSIS SHOWS THE SYSTEM IS IN A FAVORABLE
VERTICAL WIND SHEAR ENVIRONMENT WITH STRONG LOW LEVEL CONVERGENCE TO
THE SOUTHWEST OF THE LLCC AND STRONG UPPER LEVEL DIVERGENCE ALSO TO
THE SOUTHWEST OF THE LLCC.  SEA SURFACE TEMPERATURES REMAIN FAVORABLE
(30-31 CELSIUS).  TS 21W IS MOVING WESTWARD UNDER THE STEERING
INFLUENCE OF  A DEEP-LAYER SUBTROPICAL RIDGE (STR) TO THE NORTH.
3. FORECAST REASONING.
   A. THERE IS NO SIGNIFICANT CHANGE TO THE FORECAST PHILOSOPHY FROM
THE PREVIOUS PROGNOSTIC REASONING MESSAGE.
   B. TS DOKSURI WILL CONTINUE TO TRACK GENERALLY WESTWARD AND WILL
PASS SOUTH OF HAINAN ISLAND BEFORE EVENTUALLY MAKING LANDFALL IN
NORTHERN VIETNAM.  THE STR LOCATED TO THE NORTH WILL CONTINUE TO
BUILD KEEPING THE FORECAST TRACK WESTERLY.  ENVIRONMENTAL CONDITIONS
INCLUDING LOW LEVEL CONVERGENCE, UPPER LEVEL DIVERGENCE, VERTICAL
WIND SHEAR, AND SEA SURFACE TEMPERATURES ALL REMAIN FAVORABLE FOR THE
INTENSIFICATION OF TS 21W.  BY TAU 24 TS 21W WILL BE LOCATED OVER SEA
SURFACE TEMPERATURES IN EXCESS OF 31 CELSIUS.  THE COMBINATION OF
THESE FACTORS WILL PRODUCE MAXIMUM WINDS OF 95 KNOTS BY TAU 36.
LANDFALL IN NORTHERN VIETNAM WILL OCCUR SHORTLY AFTER TAU 36. DOKSURI
WILL THEN RAPIDLY DECREASE IN INTENSITY AND FORWARD SPEED AND
DISSIPATE BY TAU 72.  MODEL TRACK GUIDANCE REMAINS IN GOOD AGREEMENT,
LENDING HIGH CONFIDENCE IN THE JTWC TRACK FORECAST.//
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