Tropical Storm CHAN-HOM Advisory Mon Oct 12

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 16W (CHAN-HOM) WARNING
NR
030//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL DEPRESSION (TD) 16W (CHAN-HOM), LOCATED APPROXIMATELY
325
NM SOUTH-SOUTHEAST OF YOKOSUKA, JAPAN, HAS TRACKED SOUTHWARD AT 04
KNOTS (KTS) OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL
SATELLITE
IMAGERY (MSI) REVEALS A FULLY-EXPOSED LOW LEVEL CIRCULATION CENTER
(LLCC) WITH CONVECTIVE BANDING WRAPPING INTO THE CENTER. ALL
ASSOCIATED
DEEP CONVECTION HAS DISSIPATED OVER THE PAST SIX HOURS. AN 112358Z
BULLSEYE ASCAT-B IMAGE SHOWS A FEW 25-30 KT WIND BARBS IN THE
WESTERN
SEMI-CIRCLE WITH WEAKER WINDS ELSEWHERE. THIS ASCAT PASS SUPPORTS
THE
INITIAL POSITION AND INTENSITY WITH GOOD CONFIDENCE. TD 16W IS
LOCATED
IN A MARGINAL ENVIRONMENT UNDER MODERATE TO HIGH (20-25 KT) VERTICAL
WIND SHEAR (VWS). ADDITIONALLY, SIGNIFICANT DRY AIR HAS ENTRAINED
INTO
THE SYSTEM. AS IT IS EXPERIENCING SOME BAROCLINICITY, TD 16W APPEARS
TO
BE A HYBRID/SUBTROPICAL SYSTEM AND HAS AN ASYMMETRIC APPEARANCE IN
BOTH
THE WIND FIELD AND TOTAL PRECIPITABLE WATER IMAGERY. TD 16W IS
TRACKING
SOUTHWARD ALONG THE BACK EDGE OF AN UPPER-LEVEL SHORTWAVE TROUGH
AROUND
THE PERIPHERY OF A LOW-LEVEL SUBTROPICAL RIDGE (STR) POSITIONED TO
THE
WEST.
3. FORECAST REASONING.
   A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS
PROGNOSTIC REASONING MESSAGE.
   B. TD 16W IS EXPECTED TO CONTINUE GENERALLY SOUTH-SOUTHEASTWARD
AS
IT TRACKS ALONG THE EASTERN PERIPHERY OF THE LOW-LEVEL STR
THROUGHOUT
THE FORECAST PERIOD. THE SYSTEM WILL STEADILY WEAKEN DUE TO
CONTINUED
DRY AIR ENTRAINMENT AND MODERATE TO HIGH (20-25 KT) VWS. SYSTEM
DISSIPATION IS ANTICIPATED BY TAU 24. NUMERICAL MODEL GUIDANCE IS IN
GOOD AGREEMENT THROUGH TAU 24 BUT BEGINS TO DIVERGE AFTERWARDS.
OVERALL, THERE IS GOOD CONFIDENCE IN THE JTWC FORECAST TRACK. MODEL
GUIDANCE SHOWS THERE IS SOME POTENTIAL FOR TD 16W TO SLOWLY
REGENERATE
AS A WARM-CORE TROPICAL SYSTEM AFTER TAU 48 AS THE SYSTEM TRACKS
OVER
WARM SEA SURFACE TEMPERATURES (28-29 CELSIUS) AND UNDER DECREASING
VWS
(<20 KTS).//
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