WDPN32 PGTW 291500
MSGID/GENADMIN/NAVMARFCSTCEN PEARL HARBOR HI/JTWC//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 18W WARNING NR 10//
RMKS/
1. FOR METEOROLOGISTS.
2. 12 HOUR SUMMARY AND ANALYSIS.
    A. TROPICAL STORM (TS) 18W (EIGHTEEN) LOCATED APPROXIMATELY 255
NM EAST-SOUTHEAST OF GUAM, HAS TRACKED WEST-NORTHWESTWARD AT 19 KNOTS
OVER THE PAST SIX HOURS. ANIMATED INFRARED SATELLITE IMAGERY DEPICTS
DEEP CONVECTION HAS SPORADICALLY DEVELOPED OVER THE LOW LEVEL
CIRCULATION CENTER (LLCC) WITHIN THE PAST 12 HOURS AS VERTICAL WIND
SHEAR HAS DECREASED. POOR UPPER LEVEL SUPPORT HAS HINDERED 
SIGNIFICANT DEVELOPMENT OVER THE PAST 12 HOURS, WITH DVORAK ESTIMATES
INDICATING A POSSIBLE WEAKENING TREND BEGINNING. THE CLOSE PROXIMITY
TO TS 19W AND TD 20W HAS STIFFLED THE UPPER LEVEL OUTFLOW NEEDED FOR
TS 18W TO INTENSIFY. THE LOW LEVEL INFLOW INTO THE SYSTEM IS ALSO 
BEING HAMPERED BY TS 19W AND TD 20W. THE CURRENT INTENSITY IS BASED
ON DVORAK ESTIMATES FROM PGTW AND KNES AND A 290818Z QUIKSCAT PASS 
WHICH SHOWED UNFLAGGED 30 TO 35 KNOT WINDS.
3. FORECAST REASONING
    A. THE FORECAST REASONING HAS NOT CHANGED SINCE THE PREVIOUS
PROGNOSTIC REASONING BULLETIN.
    B. TS 18W IS FORECAST TO TRACK WEST-NORTHWESTWARD UNDER THE 
STEERING INFLUENCE OF THE LOW- TO MID-LEVEL SUBTROPICAL RIDGE TO THE 
NORTH THROUGH TAU 72. THE AVAILABLE MODEL GUIDANCE IS IN FAIR 
AGREEMENT WITH THIS SCENARIO. AS TS 18W TRACKS WESTWARD, IT WILL
REMAIN WEAK, AND WITH INCREASING INTERACTION WITH TS 19W FROM TAU 48
TO TAU 72, FURTHER WEAKENING IS EXPECTED UNTIL TS 18W IS ABSORBED
INTO TS 19W AROUND TAU 96.//
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