WDPN31 PGTW 171500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 20W (TALIM) WARNING NR 
36//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL STORM 20W (TALIM), LOCATED APPROXIMATELY 115 NM EAST OF
IWAKUNI, JAPAN, HAS TRACKED NORTHEASTWARD AT 26 KNOTS OVER THE
PAST SIX HOURS. THE CURRENT POSITION IS BASED ON RECENT AGENCY 
SATELLITE POSITION FIXES AND OBSERVATIONAL AND RADAR DATA FROM THE 
JAPAN METEOROLOGICAL AGENCY. THE INTENSITY OF 55 KNOTS IS CONSISTENT 
WITH SUBJECTIVE DVORAK INTENSITY ESTIMATES FROM RJTD AND SYNOPTIC 
OBSERVATIONS FROM REPORTING STATIONS ACROSS JAPAN. TS 20W HAS 
CONTINUED TO ACCELERATE NORTHEASTWARD OVER THE PAST SIX HOURS IN THE 
GRADIENT BETWEEN A SUBTROPICAL STEERING RIDGE TO THE SOUTHEAST AND A 
MID-LATITUDE TROUGH TO THE NORTHWEST. RECENT CHANGES IN KEY STORM 
CHARACTERISTICS, SUCH AS THE NOTED ACCELERATION IN FORWARD MOTION 
AND ASYMMETRIC CONVECTIVE DEVELOPMENT, INDICATE THAT TS 20W HAS 
BEGUN TO MERGE WITH THE MID-LATITUDE TROUGH, COMMENCING THE INITIAL 
STAGE OF EXTRATROPICAL TRANSITION. 
3. FORECAST REASONING.     
   A. THE FORECAST TRACK HAS AGAIN SHIFTED SLIGHTLY TO THE RIGHT 
BASED ON RECENT STORM MOTION RELATIVE TO THE PREVIOUS FORECAST. 
HOWEVER, THERE IS NO SIGNIFICANT CHANGE TO THE FORECAST PHILOSOPHY 
FROM THE PREVIOUS PROGNOSTIC REASONING MESSAGE.
   B. TS 20W WILL COMPLETE EXTRATROPICAL TRANSITION WITHIN THE NEXT 
12 HOURS AS IT TRACKS RAPIDLY NORTHEASTWARD. FAVORABLE BAROCLINIC 
INTERACTION BETWEEN TS 20W AND THE MID-LATITUDE TROUGH DURING 
EXTRATROPICAL TRANSITION WILL ALLOW THE SYSTEM TO MAINTAIN AN 
EXPANSIVE AREA OF LOW-LEVEL GALE-FORCE AND STRONGER WINDS. GIVEN THE 
SIZE OF THIS WIND FIELD, POTENTIALLY SIGNIFICANT WEATHER IMPACTS 
SHOULD BE ANTICIPATED THROUGHOUT MAINLAND JAPAN - PARTICULARLY IN 
COASTAL AREAS - FOR THE NEXT 24 HOURS. BASED ON CONTINUED TIGHT 
AGREEMENT AMONG FORECAST MODELS, THERE IS HIGH CONFIDENCE IN THE 
CURRENT JTWC OFFICIAL TRACK FORECAST.//
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