Tropical Storm ETAU Advisory mié, 09-09

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 18W (ETAU) WARNING NR
10//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL STORM (TS) 18W (ETAU), LOCATED APPROXIMATELY 126 NM WEST-
SOUTHWEST OF YOKOSUKA, JAPAN, HAS TRACKED NORTH-NORTHWESTWARD AT 16
KNOTS OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE
IMAGERY (MSI) DEPICTS A TIGHTLY WOUND LOW LEVEL CIRCULATION CENTER
THAT HAS MADE LANDFALL OVER CENTRAL JAPAN. WATER VAPOR IMAGERY SHOWS
AN ELONGATED CLOUD STRUCTURE THAT HAS CONTINUED TO GAIN FRONTAL
CHARACTERISTICS AS IT EMBEDS WITHIN THE BAROCLINIC ZONE. THE INITIAL
POSITION IS BASED ON THE MSI LOOP AND SUPPORTED BY RJTD RADAR FIXES
WITH GOOD CONFIDENCE. THE INITIAL INTENSITY HAS BEEN LOWERED TO 50
KNOTS BASED ON THE DETERIORATION OF THE LOW LEVEL CIRCULATION CENTER
AS THE SYSTEM INTERACTS WITH MAINLAND JAPAN. UPPER LEVEL ANALYSIS
INDICATES THAT TS 18W IS EMBEDDING IN THE BAROCLINIC ZONE WITH AN
UPPER LEVEL TROUGH ENGULFING THE SYSTEM AND PRODUCING HIGH (30-40
KNOT) SOUTHWESTERLY VERTICAL WIND SHEAR (VWS). TS ETAU IS TRACKING
BETWEEN THE WESTERN EXTENSION OF A DEEP-LAYERED SUB- TROPICAL RIDGE
(STR) TO THE NORTHEAST AND THE AFOREMENTIONED TROUGH.
3. FORECAST REASONING.
   A. THERE IS NO SIGNIFICANT CHANGE TO THE FORECAST PHILOSOPHY FROM
THE PREVIOUS PROGNOSTIC REASONING MESSAGE.
   B. TS 18W WILL CONTINUE TO TRACK TO THE NORTHWEST UNDER THE
INFLUENCE OF THE TIGHTENED GRADIENT BETWEEN THE STR AND THE UPPER
LEVEL TROUGH. THE SYSTEM WILL FURTHER WEAKEN DUE TO LAND INTERACTION
AS IT CROSSES OVER MAINLAND JAPAN. IN ADDITION, TS ETAU WILL EMBED
FURTHER INTO THE BAROCLINIC ZONE AND CONTINUE TO GAIN EXTRA-TROPICAL
CHARACTERISTICS. TS 18W WILL COMPLETE EXTRA-TROPICAL TRANSITION BY
THE END OF THE FORECAST PERIOD OR POSSIBLY SOONER AS A WEAK COLD-
CORE LOW. THE REMNANTS OF TS 18W ARE EXPECTED TO TRANSITION TO A
NORTHWESTWARD TRAJECTORY AND PASS WEST OF MISAWA. DYNAMIC MODEL
GUIDANCE IS IN GOOD OVERALL AGREEMENT THROUGHOUT THE FORECAST
PERIOD, WHICH LENDS TO HIGH CONFIDENCE IN THE JTWC FORECAST.//
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