Tropical Storm ETAU Advisory Tue Sep 08

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 18W (ETAU) WARNING NR 06//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL STORM (TS) 18W (ETAU), LOCATED APPROXIMATELY 474 NM SOUTH
OF YOKOSUKA, JAPAN, HAS TRACKED NORTHWARD AT 18 KNOTS OVER THE PAST
SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY SHOWS CONVECTIVE
BANDING - TO THE NORTH AND SOUTH - HAVE DEEPENED AND WRAPPED TIGHTER
INTO THE LOW LEVEL CIRCULATION CENTER. THE INITIAL POSITION IS LINED
UP WITH A BANDING EYE FEATURE ON THE 072251Z F18 37 GHZ MICROWAVE
IMAGE WITH FAIR CONFIDENCE. THE INITIAL INTENSITY OF 45 KNOTS IS
BASED ON AN OVERALL ASSESSMENT OF AVAILABLE DVORAK ESTIMATES AND
REFLECTS THE IMPROVED STATE OF THE CYCLONE. UPPER-LEVEL ANALYSIS
INDICATES A GENERALLY FAVORABLE ENVIRONMENT WITH LOW VERTICAL WIND
SHEAR AND ROBUST POLEWARD VENTING. TS 18W IS CURRENTLY TRACKING ALONG
THE WESTERN EXTENSION OF A DEEP-LAYERED SUBTROPICAL RIDGE (STR) TO
THE NORTHEAST.
3. FORECAST REASONING.
   A. THERE IS NO SIGNIFICANT CHANGE TO THE FORECAST PHILOSOPHY FROM
THE PREVIOUS PROGNOSTIC REASONING MESSAGE.
   B. TS 18W WILL TRACK NORTH-NORTHWESTWARD THROUGH TAU 36 ALONG THE
WESTERN PERIPHERY OF THE LOW- TO MID-LAYER REFLECTION OF THE STR. TS
18W SHOULD CONTINUE TO SLOWLY INTENSIFY THROUGH TAU 24, PEAKING AT 55
KNOTS. HOWEVER, AFTER TAU 24 THE SYSTEM WILL ENCOUNTER STRONG
VERTICAL WIND SHEAR ASSOCIATED WITH A DEEP SHORTWAVE TROUGH FORECAST
TO DIG OVER WESTERN JAPAN BY TAU 24. THIS IS IN ADDITION TO
FRICTIONAL EFFECTS AS IT MAKES LANDFALL OVER HONSHU. THESE, COMBINED
WITH COLDER SSTS IN THE SEA OF JAPAN WILL CAUSE TS 18W TO DISSIPATE
BY TAU 72. DYNAMIC GUIDANCE IS IN GOOD AGREEMENT, LENDING HIGH
CONFIDENCE TO THE JTWC FORECAST TRACK.//
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