Tropical Storm CHAN-HOM Advisory Fri Oct 09

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 16W (CHAN-HOM)
WARNING NR 015//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TYPHOON 16W (CHAN-HOM), LOCATED APPROXIMATELY 524 NM
SOUTHWEST OF YOKOSUKA, JAPAN, HAS TRACKED NORTHWARD AT 09 KNOTS
OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY
(MSI) DEPICTS SPIRAL BANDS OF DEEP CONVECTION WRAPPING INTO A
RAGGED, 30 NM DIAMETER EYE. THE INITIAL POSITION IS PLACED WITH
HIGH CONFIDENCE BASED ON THE EYE FEATURE IN THE MSI LOOP. THE
INITIAL INTENSITY OF 80 KTS IS PLACED WITH HIGH CONFIDENCE AND IS
HEDGED ABOVE MULTI-AGENCY DVORAK CURRENT INTENSITY ESTIMATES OF
T4.0 (65 KTS, RJTD) AND T4.5 (77 KTS, PGTW AND KNES) BASED ON A
TIMELY 080119Z CIMSS SATCON INTENSITY ESTIMATE OF 86 KTS. TY 16W
IS TRACKING ALONG THE WESTERN PERIPHERY OF A SUBTROPICAL RIDGE
(STR) POSITIONED TO THE EAST AND THROUGH AN ENVIRONMENT THAT HAS
REMAINED FAVORABLE FOR DEVELOPMENT OVER THE PAST 6 HOURS WITH
LOW (10-15 KTS) VERTICAL WIND SHEAR (VWS), WARM (27-28 CELSIUS)
SEA SURFACE TEMPERATURE (SST) AND ROBUST POLEWARD AND EQUATORWARD
OUTFLOW ALOFT. THE POLEWARD OUTFLOW CONTINUES TO BE ENHANCED BY
THE WESTERLY FLOW OF THE JET POSITIONED TO THE NORTH OVER JAPAN.
3. FORECAST REASONING.
   A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS
PROGNOSTIC REASONING MESSAGE.
   B. TY CHAN-HOM WILL CONTINUE TO TRACK GENERALLY NORTHWARD
AS IT ROUNDS THE STR AXIS THROUGH TAU 24. THE SYSTEM WILL BEGIN
TO GRADUALLY WEAKEN TO 70 KTS BY TAU 24 DUE TO INCREASING VWS
ASSOCIATED WITH THE AFOREMENTIONED WESTERLY FLOW ALOFT. AFTER
ROUNDING THE STR THE SYSTEM WILL BEGIN TO INTERACT WITH THE
BAROCLINIC ZONE AND TRACK GENERALLY NORTHEASTWARD. THIS
INTERACTION WILL CAUSE THE SYSTEM TO BEGIN EXTRATROPICAL TRANSITION
(ETT) BY TAU 36. TY CHAN-HOM WILL CONTINUE TO WEAKEN TO 50 KTS BY
TAU 72 AS VWS INCREASES AND SST DECREASES TO 25-26 CELSIUS. BY THIS
TIME, THE SYSTEM WILL BECOME FULLY EMBEDDED IN THE BAROCLINIC ZONE
AND COMPLETE ETT. NUMERICAL MODEL TRACK GUIDANCE IS IN ONLY FAIR
AGREEMENT WITH A MAXIMUM 370 NM ACROSS TRACK SPREAD IN SOLUTIONS BY
TAU 72. ALL INTERESTS IN THE KANTO PLAIN REGION OF JAPAN SHOULD PAY
CLOSE ATTENTION TO THE TIMING OF THE NORTHEASTWARD TURN AND
EVOLUTION OF THE WIND FIELD, GIVEN THE EXTENSIVE AMBIENT
NORTHEASTERLY FLOW. OVERALL, THE SPREAD IN MODEL SOLUTIONS LENDS
ONLY FAIR CONFIDENCE IN THIS INITIAL PORTION OF THE JTWC FORECAST
TRACK.
   C. AFTER TAU 72, THE SYSTEM WILL CONTINUE TO ACCELERATE EAST-
NORTHEASTWARD AS IT MOVES AWAY FROM JAPAN AS A COLD CORE LOW. WINDS
WILL REMAIN SIGNIFICANT DUE TO THE FRONTAL NATURE OF THE SYSTEM,
HOWEVER HIGH (50+ KTS) VWS WILL FURTHER WEAKEN THE SYSTEM TO 45 KTS
BY THIS TIME. THE SPREAD IN NUMERICAL MODEL SOLUTIONS INCREASES
DURING THIS PORTION OF THE FORECAST TO 960 NM AND THEREFORE LENDS
OVERALL POOR CONFIDENCE IN THE REMAINDER OF THE JTWC FORECAST TRACK.
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