Tropical Storm CHABA Advisory Mi, 05.10.

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 21W (CHABA) WARNING NR 29//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TYPHOON (TY) 21W (CHABA), LOCATED APPROXIMATELY 100 NM NORTHWEST
OF SASEBO, JAPAN, HAS TRACKED NORTHEASTWARD AT 20 KNOTS OVER THE
PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY DEPICTS A
RAPIDLY DETERIORATING SYSTEM WITH AN EXPOSED, BROADENING LOW-LEVEL
CIRCULATION CENTER (LLCC) LOCATED ON THE SOUTHWEST EDGE OF THE
DECAYING DEEP CONVECTION. THE CENTER HAS TRACKED JUST SOUTH OF
BUSAN, KOREA, WHICH IS REPORTING EAST-NORTHEASTERLY TO NORTHEASTERLY
SUSTAINED WINDS OF 45 KNOTS WITH GUSTS UP TO 55 KNOTS. RECENT JMA
RADAR IMAGERY SHOWS A FRONTAL-LIKE CONVECTIVE PATTERN, AND PROVIDES
EVIDENCE THAT THE SYSTEM IS UNDERGOING EXTRA-TROPICAL TRANSITION
(ETT). THE CURRENT POSITION IS BASED ON RADAR FIXES AND A 042156Z
WINDSAT 37GHZ MICROWAVE EYE FEATURE. THE CURRENT INTENSITY IS
ASSESSED AT 75 KNOTS BASED ON THE DVORAK CURRENT INTENSITY ESTIMATES
OF 77 KNOTS (4.5) FROM PGTW AND KNES. UPPER-LEVEL ANALYSIS INDICATES
STRONG SOUTHWESTERLY VERTICAL WIND SHEAR (VWS) OFFSET SLIGHTLY BY
ENHANCED POLEWARD OUTFLOW. TY CHABA IS TRACKING NORTHEASTWARD ALONG
THE NORTHWEST PERIPHERY OF THE DEEP-LAYERED SUBTROPICAL RIDGE (STR).
3. FORECAST REASONING.
   A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS
PROGNOSTIC REASONING MESSAGE.
   B. TY CHABA WILL CONTINUE TO ACCELERATE NORTHEASTWARD AS IT
ROUNDS THE STR AXIS AND ENTERS THE MIDLATITUDE WESTERLIES.
SIGNIFICANT WEAKENING IS EXPECTED TO OCCUR DUE TO COOLER SSTS AND
INCREASING VWS. THE SYSTEM IS EXPECTED TO COMPLETE ETT BY TAU 24 AS
IT GAINS FRONTAL CHARACTERISTICS AND BECOMES EMBEDDED WITHIN THE
MIDLATITUDE WESTERLIES. DYNAMIC GUIDANCE REMAINS IN TIGHT AGREEMENT,
THEREFORE, THERE IS HIGH CONFIDENCE IN THE JTWC FORECAST TRACK.//
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