WDPN31 PGTW 092100
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 16W (CHAN-HOM) WARNING 
NR 021//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL STORM (TS) 16W (CHAN-HOM), LOCATED APPROXIMATELY 343 NM 
SOUTHWEST OF YOKOSUKA, JAPAN, HAS TRACKED EAST-NORTHEASTWARD AT 07 
KNOTS (KTS) OVER THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED 
(EIR) SATELLITE IMAGERY DEPICTS A FULLY-EXPOSED LOW LEVEL 
CIRCULATION CENTER WITH ASSOCIATED CONVECTION SHEARED TO THE 
NORTHEAST. THE INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE BASED 
ON THE FULLY-EXPOSED NATURE OF THE LLCC AND LOW LEVEL FEATURES 
EVIDENT IN A 091629Z AMSR2 89 GHZ MICROWAVE IMAGE. THE INITIAL 
INTENSITY IS SET AT 50 KTS AND IS SUPPORTED BY MULTI-AGENCY DVORAK 
INTENSITY ESTIMATES RANGING FROM T2.5-3.5 (35-55 KTS) AND A 091740Z 
ADVANCED DVORAK TECHNIQUE ESTIMATE OF T2.8 (43 KTS). A 091627Z AMSR2 
WINDSPEED PRODUCT REVEALS SWATHS OF 50 KT WINDS AROUND THE LLCC, 
LENDING GOOD CONFIDENCE TO THE INITIAL INTENSITY. UPPER LEVEL 
ANALYSIS REVEALS A ROBUST POLEWARD OUTFLOW CHANNEL ASSOCIATED WITH 
THE JET POSITIONED OVER JAPAN 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 DEVELOPMENT ALONG THE NORTHERN PERIPHERY 
OF A SUBTROPICAL RIDGE. THE SYSTEM IS TRACKING ALONG THE EDGE OF THE 
BAROCLINIC ZONE AND HAS BEGUN SUBTROPICAL TRANSITION (STT) AS IT 
BEGINS TO EXHIBIT A COMBINATION OF TROPICAL AND EXTRATROPICAL 
CHARACTERISTICS.
3. FORECAST REASONING.
   A. THE FORECAST PHILOSOPHY HAS SHIFTED FROM AN EXTRATROPICAL 
TRANSITION TO A DISSIPATION SCENARIO IN THIS PROGNOSTIC REASONING 
BASED ON MODEL GUIDANCE. 
   B. TS 16W WILL CONTINUE TO TRACK EAST-NORTHEASTWARD THEN EASTWARD 
THROUGH TAU 24 AS IT CONTINUES STT, INTERACTING WITH THE BAROCLINIC 
ZONE TO THE NORTH. PERSISTENTLY HIGH VWS WILL LEAD TO STEADY 
WEAKENING TO 40 KTS BY TAU 24. AFTER THIS, THE SYSTEM WILL TURN TO A 
SOUTHEASTWARD TRACK AS A BREAK APPEARS WITHIN THE STR. ALONG THIS 
TRACK, THE SYSTEM WILL RAPIDLY WEAKEN DUE TO HIGH VWS VALUES AND DRY 
AIR ENTRAINMENT. NUMERICAL MODEL GUIDANCE IS IN GOOD AGREEMENT 
THROUGH TAU 24. AFTERWARDS, ALL MODEL SOLUTIONS BEGIN TO TURN THE 
SYSTEM TO THE SOUTHEAST WITH SPREAD INCREASING TO 202 NM BY TAU 48. 
THIS DIVERGENCE IN TRACK GUIDANCE PLACES OVERALL POOR CONFIDENCE IN 
THE JTWC FORECAST TRACK, WHICH IS PLACED NEAR THE MULTI-MODEL 
CONSENSUS AND THE ECMWF TRACK SOLUTION.//
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