Tropical Storm CHAN-HOM Advisory Sat Oct 10

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 16W (CHAN-HOM) WARNING
NR 022//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL STORM (TS) 16W (CHAN-HOM), LOCATED APPROXIMATELY 281 NM
SOUTHWEST OF YOKOSUKA, JAPAN, HAS TRACKED NORTHEASTWARD AT 10 KNOTS
(KTS) OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE
IMAGERY (MSI) REVEALS A FULLY-EXPOSED LOW LEVEL CIRCULATION CENTER
(LLCC) WITH THE ASSOCIATED CONVECTION SHEARED TO THE NORTHEAST. A
092325Z ASCAT-A IMAGE SHOWS AN ASYMMETRIC WIND FIELD WITH A SWATH OF
50-54 KT WINDS IN THE NORTHWEST QUADRANT. BASED ON THE ASCAT IMAGE
AND FULLY-EXPOSED NATURE, THERE IS HIGH CONFIDENCE IN THE INITIAL
POSITION OF TS 16W. THE INITIAL INTENSITY IS SET AT 50 KTS WITH GOOD
CONFIDENCE AND IS HEDGED SLIGHTLY HIGHER THAN AN ADVANCED DVORAK
TECHNIQUE ESTIMATE OF T2.7 (39 KTS) AND A 092112Z SATCON ESTIMATE OF
44 KTS BASED ON THE AFOREMENTIONED ASCAT DATA. UPPER LEVEL ANALYSIS
REVEALS A ROBUST POLEWARD OUTFLOW CHANNEL ASSOCIATED WITH THE JET
BEING OFFSET BY HIGH (>30 KT) VERTICAL WIND SHEAR (VWS) VALUES. SEA
SURFACE TEMPERATURES (SST) REMAIN CONDUCIVE AT 26-27 CELSIUS.
OVERALL, TS 16W IS TRACKING THROUGH AN UNFAVORABLE ENVIRONMENT FOR
CONTINUED DEVELOPMENT AS IT TRANSITS ALONG THE NORTHERN PERIPHERY OF
A SUBTROPICAL RIDGE (STR) POSITIONED TO THE SOUTH. THE SYSTEM IS
TRACKING ALONG THE BAROCLINIC ZONE AND HAS BEGUN SUBTROPICAL
TRANSITION (STT) AS IT IS BEGINNING TO EXHIBIT A COMBINATION OF
TROPICAL AND EXTRATROPICAL CHARACTERISTICS.
3. FORECAST REASONING.
   A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS
PROGNOSTIC REASONING MESSAGE.
   B. THROUGH TAU 24, TS 16W WILL TRACK GENERALLY EASTWARD AS IT
CONTINUES STT, INTERACTING WITH THE BAROCLINIC ZONE TO THE NORTH.
PERSISTENT HIGH VWS WILL LEAD TO STEADY WEAKENING TO 40 KTS BY TAU
24. AFTER THIS, THE STR WILL REORIENT, CAUSING THE SYSTEM TO TURN TO
A SOUTHEASTWARD TRACK AS A BREAK APPEARS WITHIN THE STR. HIGH VWS
VALUES AND DRY AIR ENTRAINMENT WILL RAPIDLY WEAKEN TS 16W ALONG THIS
TRACK, LEADING TO DISSIPATION BY TAU 48. THROUGHOUT THE FORECAST
PERIOD, NUMERICAL MODEL GUIDANCE DIVERGES WITH GFS AND GFS ENSEMBLE
SOLUTION DEPICTING THE TIGHTEST TURN TO THE SOUTH WHILE THE NAVGEM
SOLUTION SHOWS THE SYSTEM TRACKING FURTHER EAST PRIOR TO TURNING
SOUTHEASTWARD. NUMERICAL MODEL SPREAD AT TAU 48 IS 167 NM. DUE TO
THE DIVERGENCE IN TRACK GUIDANCE, THERE IS OVERALL FAIR CONFIDENCE
IN THE JTWC FORECAST TRACK, WHICH IS PLACED NEAR THE MULTI-MODEL
CONSENSUS AND THE ECMWF TRACK SOLUTION.//
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