Tropical Storm TALIM Advisory Mon Sep 18

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 20W (TALIM) WARNING NR
35//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL STORM 20W (TALIM), LOCATED APPROXIMATELY 114 NM SOUTH OF
IWAKUNI, JAPAN, HAS TRACKED NORTHEASTWARD AT 21 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 MULTIPLE REPORTING
AGENCIES, A VARIETY OF AUTOMATED SATELLITE INTENSITY ESTIMATES AND
SCATTEROMETER DATA FROM A 170130Z ASCAT PASS. TS 20W IS ACCELERATING
NORTHEASTWARD ALONG THE NORTHWESTERN PERIPHERY OF A SUBTROPICAL
STEERING RIDGE, AND IS MERGING INTO THE FLOW ASSOCIATED WITH AN
APPROACHING MID-LATITUDE TROUGH. STRONG UPPER-LEVEL DIVERGENCE AHEAD
OF THE TROUGH HAS FUELED A FLAIR OF DEEP CONVECTION OVER THE
NORTHERN PORTION OF THE CIRCULATION OVER THE PAST SEVERAL HOURS.
3. FORECAST REASONING.
   A. THE FORECAST TRACK HAS 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 CONTINUE TO ACCELERATE NORTHEASTWARD AS IT MERGES
WITH THE AFOREMENTIONED MID-LATITUDE TROUGH OVER THE NEXT DAY AND A
HALF. EXTRATROPICAL TRANSITION WILL BEGIN SHORTLY, COMPLETING BY TAU
24. FAVORABLE BAROCLINIC INTERACTION BETWEEN TS 20W AND THE TROUGH
DURING EXTRATROPICAL TRANSITION WILL ALLOW THE SYSTEM TO MAINTAIN A
STRONG AND EXPANSIVE LOW-LEVEL WIND FIELD. IN FACT, THE OVER-WATER
AREA INFLUENCED BY GALE-FORCE WINDS IS EXPECTED TO GROW THROUGHOUT
THE FORECAST PERIOD. GIVEN THE SIZE OF THIS WIND FIELD, POTENTIALLY
SIGNIFICANT WEATHER IMPACTS SHOULD BE ANTICIPATED THROUGHOUT
MAINLAND JAPAN - PARTICULARLY IN COASTAL AREAS - FOR THE NEXT 36
HOURS. GIVEN CONTINUED STRONG AGREEMENT AMONG FORECAST MODELS, THERE
IS HIGH CONFIDENCE IN THE CURRENT JTWC OFFICIAL TRACK FORECAST.//
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