Tropical Storm CHABA Advisory Wed Oct 05

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 21W (CHABA) WARNING NR 26//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TYPHOON 21W (CHABA), LOCATED APPROXIMATELY 204 NM NORTH-NORTHWEST
OF KADENA AB, HAS TRACKED NORTHWARD AT 16 KNOTS OVER THE PAST SIX
HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY DEPICTS AN 11 NM
RAGGED EYE FEATURE THAT IS SLIGHTLY CLOUD FILLED, GIVING HIGH
CONFIDENCE TO THE INITIAL POSITION, AND ALSO SHOWING A WEAKENING
CONVECTIVE STRUCTURE. THE INITIAL INTENSITY IS ASSESSED AT 120 KNOTS
AND IS BASED ON A CURRENT SATCON ESTIMATE OF 122 KNOTS AND CURRENT
INTENSITY DVORAK ESTIMATES RANGING FROM T6.0 TO T6.5 (115 TO 127
KNOTS). UPPER-LEVEL ANALYSIS SHOWS VERY STRONG DUAL CHANNEL OUTFLOW,
HOWEVER, SOUTHWESTERLY VERTICAL WIND SHEAR IS BEGINNING TO INCREASE.
SEA SURFACE TEMPERATURES ARE FAVORABLE NEAR 28 CELSIUS. CURRENTLY,
TY CHABA IS TRACKING NORTHWARD ALONG THE WESTERN PERIPHERY OF A DEEP-
LAYERED SUBTROPICAL RIDGE POSITIONED OFF TO THE EAST.
3. FORECAST REASONING.
   A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS
PROGNOSTIC REASONING MESSAGE.
   B. TY CHABA WILL CONTINUE TO TRACK ALONG THE PERIPHERY OF THE
CURRENT STEERING RIDGE TURNING NORTHEAST AS IT ROUNDS THE RIDGE
AXIS. SIGNIFICANT WEAKENING IS EXPECTED TO OCCUR AS SSTS WILL
SIGNIFICANTLY DROP OVER THE NEXT 24 HOURS, AND VERTICAL WIND SHEAR
WILL INCREASE AS TY CHABA APPROACHES THE STRONG WESTERLY FLOW ALOFT.
EXTRATROPICAL TRANSITION WILL BEGIN SOMETIME BETWEEN TAU 12 TO 24 AS
THE SYSTEM IS DRIVEN INTO THE BAROCLINIC ZONE OVER THE SEA OF JAPAN.
TY CHABA IS EXPECTED TO BE A FULLY EXTRATROPICAL SYSTEM BY TAU 48.
DYNAMIC MODEL GUIDANCE IS STILL IN VERY GOOD AGREEMENT GIVING HIGH
CONFIDENCE TO THE FORECAST TRACK.//
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