Tropical Storm VICENTE Advisory Mo, 23-07

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 09W (VICENTE) WARNING
NR 07//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL STORM 09W (VICENTE), LOCATED APPROXIMATELY 215 NM SOUTH-
SOUTHEAST OF HONG KONG, HAS TRACKED WEST-SOUTHWESTWARD AT 06 KNOTS
OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY
(MSI) SHOWS DEEP CENTRALIZED CONVECTION HAS BUILT STEADILY OVER THE
PAST 12 HOURS AS THE LOW LEVEL CIRCULATION CENTER (LLCC) HAS SEEN
SIGNIFICANT STRUCTURAL IMPROVEMENTS, WHICH ARE READILY APPARENT IN A
220143Z ASCAT PASS. MSI ALSO APPEARS TO INDICATE THE LLCC HAS TAKEN
A BRIEF TURN TO THE WEST-SOUTHWEST OVER THE PAST SIX HOURS AND HAS
STARTED TO SLOW. THE CURRENT POSITION IS BASED ON AN OVERSHOOTING
TOP THAT IS VISIBLE IN MSI. THE CURRENT INTENSITY HAS BEEN
MAINTAINED AT 45 KNOTS BASED ON THE 220143Z ASCAT PASS SHOWING 40 TO
45 KNOT WINDS. UPPER LEVEL ANALYSIS INDICATES THE MICRO-SCALE
ANTICYCLONE CONTINUES TO BUILD OVER THE LLCC AND IS SUPPORTING THE
EQUATORIAL OUTFLOW. HOWEVER, INDUCED UPPER-LEVEL TROUGHING EXISTS
BETWEEN THIS SMALLER ANTICYCLONE AND A POINT SOURCE OF DIVERGENCE TO
THE SOUTHEAST OF THE SYSTEM, WHICH IS INDUCING UPPER-LEVEL
CONVERGENCE EAST OF THE LLCC. TS 09W IS CURRENTLY BEING STEERED BY
THE SOUTHERN PERIPHERY OF A ZONAL DEEP-LAYERED SUBTROPICAL RIDGE
(STR) ANCHORED OVER EASTERN ASIA AND IS UNDER MODERATE 15-20 KNOT
EASTERLY VERTICAL WIND SHEAR (VWS). A MID-LATITUDE TROUGH OVER
NORTHEASTERN CHINA HAS CREATED A SLIGHT WEAKENING OF THE STR, AND IS
CAUSING THE TRACK SPEED SLOWDOWN OBSERVED IN THE PAST 24 HOURS.
THERE IS GOOD CONFIDENCE IN THE POSITIONING OF THE LLCC BASED ON THE
AVAILABLE ASCAT PASS AND MSI.
3. FORECAST REASONING.
   A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS
PROGNOSTIC REASONING MESSAGE.
   B. TS 09W WILL SLOWLY TRACK IN A GENERAL WESTWARD DIRECTION UNDER
THE INFLUENCE OF THE STR. AS THE MID-LATITUDE TROUGH TRACKS INTO THE
MID-PACIFIC, THE STR IS EXPECTED TO STRENGTHEN, CAUSING TRACK SPEEDS
TO INCREASE THROUGH TAU 72. TS 09W SHOULD GRADUALLY INTENSIFY AS
UPPER-LEVEL CONDITIONS IMPROVE OVER THE NEXT 36-48 HOURS. BY TAU 48
THE LLCC WILL ENCOUNTER COMPETING INFLUENCES FROM LAND INTERACTION
WITH THE COASTLINE WEST OF THE LUICHOW PENINSULA AND WARM SST (28-30
CELSIUS) IN THE GULF OF TONKIN BUT SHOULD BE ABLE TO MAINTAIN STRONG
TS STRENGTH AS IT APPROACHES NORTHERN VIETNAM BY TAU 72.
   C. TS 09W SHOULD DISSIPATE OVER LAND BY TAU 96. NUMERICAL MODEL
GUIDANCE REMAINS IN GOOD AGREEMENT FOR TRACK AND APPEARS TO HAVE
COME INTO BETTER AGREEMENT ON THE TIMING IN THE EARLY FORECAST
PERIODS, BUT GREATER VARIABILITY IN THE LATER TAUS. DESPITE THESE
TRANSLATION SPEED DISCREPANCIES, HIGH CONFIDENCE REMAINS IN THE
OFFICIAL JTWC TRACK FORECAST DUE TO THE WELL ESTABLISHED SYNOPTIC
ENVIRONMENT.//
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