Tropical Storm ETAU Advisory 09 Σεπ.

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 18W (ETAU) WARNING NR
09//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL STORM (TS) 18W (ETAU), LOCATED APPROXIMATELY 147 NM
SOUTHWEST OF YOKOSUKA, JAPAN, HAS TRACKED NORTHWARD AT 21 KNOTS OVER
THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED SATELLITE IMAGERY
SHOWS A BROAD AND ELONGATED SYSTEM THAT RECENTLY UNDERWENT A FLARE
UP IN CONVECTION JUST PRIOR TO INTERACTING WITH THE JAPANESE
COASTLINE. HOWEVER, OVER THE PAST TWO HOURS THAT CONVECTION HAS
STARTED TO DISSIPATE. IN ADDITION, WATER VAPOR IMAGERY SHOWS THAT
THE SYSTEM IS BEGINNING TO INTERACT WITH THE BOUNDARY LAYER AND
STARTING EXTRA-TROPICAL TRANSITION (ETT). AN 081752Z SSMI 37GHZ
MICROWAVE IMAGE SHOWS TIGHT CURVED BANDING AT THE SURFACE WHICH, IN
CONJUNCTION WITH RJTD RADAR FIXES, SUPPORTS THE CURRENT POSITION
WITH GOOD CONFIDENCE. THE INITIAL INTENSITY IS ASSESSED AT 55 KNOTS
BASED ON AN OLDER ASCAT PASS AND CONCURRING DVORAK INTENSITY
ESTIMATES OF T3.5 (55 KNOTS) FROM ALL AGENCIES. UPPER LEVEL ANALYSIS
INDICATES THAT TS 18W IS BEGINNING TO EMBED 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; HOWEVER, WIND RADII HAVE
BEEN ENLARGED BASED ON AN 081130Z ASCAT PASS.
   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 ETT BY THE END OF THE FORECAST
PERIOD OR POSSIBLY SOONER AS A WEAK COLD-CORE LOW. DYNAMIC MODEL
GUIDANCE IS IN GOOD OVERALL AGREEMENT THROUGH THE FORECAST PERIOD,
WHICH LEND TO HIGH CONFIDENCE IN THE JTWC FORECAST.//
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