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 004//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL DEPRESSION (TD) 26W (KROVANH), LOCATED APPROXIMATELY
447 NM EAST OF HO CHI MINH CITY, VIETNAM, HAS TRACKED WEST-
SOUTHWESTWARD AT 06 KNOTS OVER THE PAST SIX HOURS. ANIMATED ENHANCED
INFRARED SATELLITE IMAGERY DEPICTS MULTIPLE VORTICES FORMING WITHIN
A BROAD LOW-LEVEL CIRCULATION (LLC) WITH ISOLATED DEEP CONVECTION
FLARING ALONG THE SOUTHWEST QUADRANT. A 201402Z MHS 89GHZ COMPOSITE
IMAGE INDICATES A BROAD, DISORGANIZED LLC WITH FRAGMENTED SHALLOW
BANDING WRAPPING AROUND THE LLC AND NO DEEP CONVECTIVE BANDING. A
201401Z ASCAT-B IMAGE ALSO SHOWS AN ELONGATED CIRCULATION, ORIENTED
NNE-SSW, WITH TWO DISCRETE CIRCULATIONS ADJACENT TO EXTENSIVE 30-35
KNOT NORTHEASTERLY SURGE WINDS. THE INITIAL POSITION IS EXTRAPOLATED
FROM THE NORTHERN CIRCULATION POSITION IN ASCAT IMAGERY. THE INITIAL
INTENSITY REMAINS ASSESSED AT 30 KNOTS BASED ON THE OVERALL WIND
FIELD / WEAK CONVECTIVE STRUCTURE, AND T1.0-1.5 (25 KNOTS) DVORAK
SUBJECTIVE ESTIMATES AND A 201830Z ADT OBJECTIVE ESTIMATE OF 2.3 (33
KNOTS). UPPER-LEVEL ANALYSIS REVEALS A MARGINAL ENVIRONMENT WITH
HIGH (25 KNOTS) VERTICAL WIND SHEAR OFFSET BY STRONG POLEWARD
OUTFLOW. SST VALUES (28-29C) REMAIN CONDUCIVE. THE SYSTEM IS
TRACKING SLOWLY 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 72. THE
SYSTEM IS FORECAST TO INTENSIFY SLIGHTLY OVER THE NEXT 12-24 HOURS
AS VWS DECREASES TO MODERATE LEVELS (15 KNOTS) WITH PERSISTENT
POLEWARD OUTFLOW. AFTER TAU 24, TD 26W SHOULD WEAKEN STEADILY AS IT
TRACKS AWAY FROM THE STRONG SURGE FLOW AND UPPER-LEVEL DIVERGENCE
DECREASES. THE SYSTEM IS FORECAST TO DISSIPATE SOUTH OF VIETNAM BY
TAU 72. THE BULK OF NUMERICAL MODEL GUIDANCE SUPPORTS THE JTWC
FORECAST TRACK, HOWEVER, THERE IS LOW OVERALL CONFIDENCE IN THE
TRACK DUE TO HIGH UNCERTAINTY IN THE INITIAL POSITION.//
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