Tropical Storm KROVANH Advisory 12月21日

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 26W (KROVANH)
WARNING NR 008//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL DEPRESSION (TD) 26W (KROVANH), LOCATED APPROXIMATELY
311 NM EAST-SOUTHEAST OF HO CHI MINH CITY, VIETNAM, HAS TRACKED
WEST-SOUTHWESTWARD AT 07 KNOTS OVER THE PAST SIX HOURS. ANIMATED
ENHANCED INFRARED SATELLITE IMAGERY INDICATES AN OBSCURED, BROAD LOW-
LEVEL CIRCULATION (LLC) WITH DEEP CONVECTION DISPLACED TO THE NORTH.
DUE TO THE OBSCURED LLC AND LACK OF RECENT MICROWAVE IMAGERY, THE
INITIAL POSITION IS EXTRAPOLATED FROM A 211341Z MHS 89GHZ COMPOSITE
MICROWAVE IMAGE AND A 211342Z ASCAT-B IMAGE, WHICH SHOW A BROAD YET
DEFINED LLC. ADDITIONALLY, THE SYSTEM CENTER TRACKED OVER TRUONG SA
(48920) AND IS NOW APPROACHING HUYEN TRAN (48919), WHICH SHOWS
SURFACE WINDS FROM THE NNW AT 17 KNOTS WITH SLP 1003.9MB (4MB
PRESSURE FALL PAST 24 HOURS) AND SUPPORTS THE INITIAL POSITION
ASSESSMENT. THE INITIAL INTENSITY REMAINS ASSESSED AT 30 KNOTS BASED
ON RECENT ASCAT DATA, AND DVORAK CURRENT INTENSITY ESTIMATES OF 1.0-
1.5 (25 KNOTS) AND A 211830Z ADT OBJECTIVE ESTIMATE OF 2.4 (34
KNOTS). UPPER-LEVEL ANALYSIS REVEALS A MARGINAL ENVIRONMENT
WITH MODERATE (20 KNOTS) VERTICAL WIND SHEAR OFFSET BY STRONG
POLEWARD OUTFLOW. SST VALUES (27-28C) REMAIN CONDUCIVE. THE SYSTEM
IS TRACKING WEST-SOUTHWESTWARD ALONG THE SOUTHEAST PERIPHERY OF
A LOW-LEVEL SUBTROPICAL RIDGE POSITIONED TO THE NORTHWEST.
3. FORECAST REASONING.
   A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS
PROGNOSTIC REASONING MESSAGE.
   B. TD 26W IS EXPECTED TO TRACK WEST-SOUTHWESTWARD TO WESTWARD
ALONG THE SOUTHERN FLANK OF THE LOW-LEVEL STR THROUGH TAU 36. THE
SYSTEM IS FORECAST TO MAINTAIN INTENSITY OVER THE NEXT 12 HOURS THEN
WILL WEAKEN STEADILY AS IT TRACKS AWAY FROM THE STRONG SURGE FLOW
OVER COOLER WATER (25-26C) WITH WEAK UPPER-LEVEL DIVERGENCE. THE
SYSTEM IS FORECAST TO DISSIPATE SOUTH OF VIETNAM BY TAU 36. THE BULK
OF THE NUMERICAL MODEL GUIDANCE SUPPORTS THE JTWC FORECAST TRACK
WITH MODERATE CONFIDENCE, HOWEVER, THERE IS SOME UNCERTAINTY IN THE
INITIAL POSITION.//
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