Tropical Storm MEGI Advisory 23 Σεπ.

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 20W (MEGI)
WARNING NR 01//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL DEPRESSION 20W (MEGI), LOCATED APPROXIMATELY 1170 NM
EAST-SOUTHEAST OF TAIPEI, TAIWAN, HAS TRACKED NORTH-NORTHWESTWARD
AT 13 KNOTS OVER THE PAST SIX HOURS. THE CURRENT POSITION IS BASED
ON ANIMATED MULTISPECTRAL SATELLITE IMAGERY, SATELLITE FIXES FROM
RJTD AND PGTW, AND A 222136Z SSMIS PASS. THERE IS LOW CONFIDENCE IN
THE INITIAL POSITION GIVEN A DISPARITY IN FIXES AND LACK OF A CLEAR,
DEFINITIVE CENTER FEATURE IN RECENT SATELLITE IMAGERY. THE INTENSITY
OF 30 KNOTS IS CONSISTENT WITH SUBJECTIVE DVORAK INTENSITY ESTIMATES
FROM ALL REPORTING AGENCIES. TD 20W HAS CONSOLIDATED FROM A BROAD
MONSOONAL CIRCULATION INTO A TROPICAL DEPRESSION OVER THE PAST SIX
HOURS, WITH TIGHTLY-WRAPPED, DEEP CONVECTIVE BANDING NOW EVIDENT IN
MULTISPECTRAL SATELLITE IMAGERY. UPPER-LEVEL RIDGING NEAR THE
CIRCULATION AND TROPICAL UPPER-TROPOSPHERIC TROUGH (TUTT) CELLS TO
THE NORTH AND WEST ARE PROVIDING STRONG UPPER-LEVEL OUTFLOW,
SUPPORTING DEVELOPMENT.
3. FORECAST REASONING.
    A. THIS IS THE FIRST PROGNOSTIC REASONING MESSAGE FOR 20W AND
SETS THE FORECAST PHILOSOPHY
    B. TD 20W IS EXPECTED TO TURN WEST-NORTHWESTWARD OVER THE NEXT
12 HOURS AND CONTINUE ALONG A GENERALLY WEST-NORTHWESTWARD
TRAJECTORY OVER THE NEXT 24 HOURS FOLLOWING THE FLOW ASSOCIATED WITH
A SUBTROPICAL STEERING RIDGE TO THE NORTH. STEADY INTENSIFICATION IS
ANTICIPATED AS THE SYSTEM CONTINUES TO CONSOLIDATE, SUPPORTED BY
STRONG UPPER-LEVEL OUTFLOW, LOW TO MODERATE VERTICAL WIND SHEAR AND
PASSAGE OVER WARM WATER. THE AVAILABLE NUMERICAL MODEL TRACK
FORECAST GUIDANCE IS IN GOOD AGREEMENT, WITH ALL SOLUTIONS
INDICATING A TRACK TOWARD OR NEAR TAIWAN OVER THE NEXT SEVERAL DAYS.
THE CURRENT FORECAST LIES CLOSE TO THE MULTI-MODEL CONSENSUS WITH
HIGH CONFIDENCE, EXCEPT IN THE VERY NEAR TERM DUE TO NOTED
UNCERTAINTY IN THE CURRENT POSITION.
    C. IN THE EXTENDED PERIOD, TD 20W SHOULD CONTINUE TO TRACK WEST-
NORTHWESTWARD UNDER THE CONTINUED STEERING INFLUENCE OF THE
SUBTROPICAL RIDGE. PEAK INTENSITY IS EXPECTED TO OCCUR AROUND TAU 96
AS ENVIRONMENTAL CONDITIONS REMAIN GENERALLY FAVORABLE. THE EXACT
INTENSITY TREND AFTER TAU 96 WILL DEPEND ON IF AND HOW THE
CIRCULATION INTERACTS WITH TAIWAN. MODEL GUIDANCE REMAINS IN
GENERALLY GOOD AGREEMENT DURING THE EXTENDED PERIOD, LENDING HIGH
CONFIDENCE TO THAT PORTION OF THE TRACK FORECAST AS WELL.//
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