Tropical Storm ETAU Advisory Mon Sep 07

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 18W (EIGHTEEN)
WARNING NR 02//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL DEPRESSION 18W (EIGHTEEN), LOCATED APPROXIMATELY 187 NM
SOUTHWEST OF IWO TO, JAPAN, HAS TRACKED NORTH-NORTHWESTWARD AT 11
KNOTS OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE (MSI)
IMAGERY SHOWS THE SYSTEM HAS, FOR THE MOST PART, MAINTAINED
CONVECTIVE AND BANDING SIGNATURE WITH THE BULK OF THE CONVECTION
AMASSED TO THE NORTH OF THE LOW LEVEL CIRCULATION CENTER (LLCC). THE
INITIAL POSITION IS BASED ON THE MSI ANIMATION AND ON RECENT
MICROWAVE SATELLITE IMAGERY WITH FAIR CONFIDENCE. THE INITIAL
INTENSITY OF 30 KNOTS IS BASED ON CONGRUENT DVORAK ESTIMATES FROM
PGTW, KNES, AND RJTD. UPPER LEVEL ANALYSIS INDICATES THE SYSTEM IS
WEST OF A SUBTROPICAL HIGH IN AN AREA OF LOW TO MODERATE (10-15 KNOT)
VERTICAL WIND SHEAR (VWS). MODERATE RADIAL OUTFLOW IS PARTIALLY
OFFSETTING THE VWS AND PROVIDING VENTILATION TO THE ASSOCIATED
CONVECTION. THE CYCLONE 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. TD 18W WILL CONTINUE ALONG ITS CURRENT TRACK OVER THE NEXT 48
HOURS. AFTERWARDS, THE STR IS FORECAST TO REORIENT AND CAUSE THE
SYSTEM TO TRACK MORE NORTHWESTWARD. TD 18W IS EXPECTED TO SLOWLY
INTENSIFY AS POLEWARD OUTFLOW INCREASES, PEAKING AT 55 KNOTS BY TAU
48. AFTER TAU 48, INCREASING VWS AND INTERACTION WITH A FRONTAL
BOUNDARY WILL RAPIDLY ERODE THE SYSTEM BEFORE IT MAKES LANDFALL OVER
SOUTHERN HONSHU, JAPAN, BEFORE TAU 72.
   C. AFTER TAU 72, TD 18W WILL DISSIPATE  AS IT EXITS THE JAPANESE
ISLANDS INTO THE SEA OF JAPAN AS IT GETS EMBEDDED IN THE BAROCLINIC
ZONE BEHIND THE AFOREMENTIONED FRONTAL BOUNDARY. THE AVAILABLE
NUMERIC GUIDANCE IS IN FAIRLY GOOD AGREEMENT UP TO TAU 36.
AFTERWARDS, THE CONSENSUS MEMBERS WIDELY SPREAD. IN VIEW OF THIS,
THERE IS AN OVERALL LOW CONFIDENCE IN THE JTWC TRACK FORECAST.//
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