Tropical Storm CHABA Advisory 01 Οκτ.

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 21W (CHABA)
WARNING NR 12//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL STORM (TS) 21W (CHABA), LOCATED APPROXIMATELY 809 NM
SOUTHEAST OF KADENA AB, OKINAWA, JAPAN, HAS TRACKED NORTHWESTWARD AT
09 KNOTS OVER THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED
SATELLITE IMAGERY INDICATES A COMPACT, CONSOLIDATING LOW-LEVEL
CIRCULATION CENTER (LLCC) WITH FRAGMENTED CONVECTIVE BANDING. THE
INITIAL POSITION IS BASED ON A LOW REFLECTIVITY CIRCULATION FEATURE
IN THE 301722Z MICROWAVE PASS WITH GOOD CONFIDENCE. THE INITIAL
INTENSITY OF 50 KNOTS IS BASED ON AN OVERALL ASSESSMENT OF OBJECTIVE
AND AGENCY DVORAK ESTIMATES AND REFLECTS THE SLIGHT, ALBEIT MOMENTARY
DEGRADATION IN THE SYSTEM. UPPER LEVEL ANALYSIS INDICATES THE SYSTEM
IS IN AN AREA OF LOW TO MODERATE (10-15 KNOT) VERTICAL WIND SHEAR
(VWS) AND GOOD RADIAL OUTFLOW. TS 21W IS TRACKING ALONG THE SOUTHWEST
PERIPHERY OF THE DEEP-LAYERED SUBTROPICAL RIDGE (STR).
3. FORECAST REASONING.
   A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS
PROGNOSTIC REASONING BULLETIN.
   B. TS CHABA WILL CONTINUE TO TRACK NORTHWESTWARD ALONG THE
SOUTHWEST PERIPHERY OF THE DEEP-LAYERED STR WHILE INTENSIFYING
STEADILY DUE TO OVERALL FAVORABLE ENVIRONMENTAL CONDITIONS. AFTER TAU
48, A MID-LATITUDE TROUGH APPROACHING FROM THE NORTHWEST WILL WEAKEN
THE STR AND CAUSE THE CYCLONE TO TRACK MORE NORTHWARD. TS 21W IS
EXPECTED TO PEAK AT 90 KNOTS NEAR TAU 72.
   C. AFTER TAU 72, TS CHABA WILL ACCELERATE NORTHEASTWARD, MAKE
LANDFALL OVER SOUTHERN KYUSHU, JAPAN, AND DRAG ACROSS SOUTHERN JAPAN.
INCREASING VWS, IN ADDITION TO LAND INTERACTION, WILL RAPIDLY ERODE
THE SYSTEM; DOWN TO 40 KNOTS BY TAU 120. CONCURRENTLY, THE SYSTEM
WILL BEGIN EXTRA-TROPICAL TRANSITION. NUMERIC MODEL GUIDANCE IS IN
TIGHT AGREEMENT UP TO TAU 72 WHERE THE CONSENSUS MEMBERS
SIGNIFICANTLY DIVERGE IN BOTH DIRECTION AND SPEED. THEREFORE, THERE
IS HIGH CONFIDENCE IN THE JTWC TRACK FORECAST UP TO TAU 72, THEN LOW
CONFIDENCE AFTERWARDS.
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