Tropical Storm CHABA Advisory ср, 05.10.

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 21W (CHABA) WARNING NR 28//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TYPHOON (TY) 21W (CHABA), LOCATED APPROXIMATELY 160 NM WEST-
SOUTHWEST OF SASEBO, JAPAN, HAS TRACKED NORTH-NORTHEASTWARD AT 15
KNOTS OVER THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED SATELLITE
IMAGERY DEPICTS A RAPIDLY DETERIORATING SYSTEM WITH DEEP CONVECTION
SHEARED OVER THE NOTHERN SEMI-CIRCLE OF A PARTIALLY-EXPOSED LOW-
LEVEL CIRCULATION CENTER (LLCC). HOWEVER, KMA RADAR IMAGERY SHOWS A
PARTIAL EYEWALL OVER THE NORTH QUADRANT OF THE LLCC AND ALSO A BROAD
CENTER JUST SOUTH TO SOUTHEAST OF CHEJU ISLAND. RADAR ANIMATION
INDICATES THAT THE CENTER IS CURRENTLY PASSING SOUTH OF THE ISLAND
AS IT RE-CURVES NORTHEASTWARD. SURFACE OBSERVATIONS FROM CHEJU
INTERNATIONAL AIRPORT (RKPC), 60NM NORTH OF THE 04/18Z CENTER
POSITION, REVEAL SUSTAINED NORTH-NORTHEASTERLY WINDS OF 45 KNOTS
GUSTING TO 68 KNOTS ASSOCIATED WITH THE EYEWALL CONVECTION. SURFACE
OBSERVATIONS FROM WESTERN KYUSHU, AHEAD OF THE SYSTEM, ARE STILL
RELATIVELY LOW AT 20 TO 30 KNOTS BUT EXPECTED TO INCREASE. A 041755Z
SSMI 85GHZ IMAGE SHOWS A DEVELOPING WEAK COLD FRONT MOVING OVER
WESTERN KYUSHU, WHICH IS INDICATIVE OF THE EARLY STAGES OF EXTRA-
TROPICAL TRANSITION (ETT). OVERALL, THERE IS GOOD CONFIDENCE IN THE
CURRENT POSITION AND RECENT TRACK MOTION CHANGE BASED ON THE
AVAILABLE RADAR IMAGERY. THE CURRENT INTENSITY IS ASSESSED AT 85
KNOTS BASED ON THE LOWER RANGE OF DVORAK INTENSITY ESTIMATES AND THE
WEAKENED STRUCTURE. UPPER-LEVEL ANALYSIS INDICATES STRONG
SOUTHWESTERLY VERTICAL WIND SHEAR (VWS) OFFSET SLIGHTLY BY ENHANCED
POLEWARD OUTFLOW. TY CHABA IS TRACKING NORTH-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. THIS EXTRATROPICAL LOW IS THEN FORECAST TO
CROSS HONSHU, WHICH WILL SERVE TO FURTHER WEAKEN THE SYSTEM. DYNAMIC
GUIDANCE REMAINS IN TIGHT AGREEMENT, THEREFORE, THERE IS HIGH
CONFIDENCE IN THE JTWC FORECAST TRACK.//
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