Tropical Storm BAVI Advisory 8月24日

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 09W (BAVI) WARNING NR
010//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
    TYPHOON 09W (BAVI), LOCATED APPROXIMATELY 127 NM WEST-NORTHWEST
OF KADENA AB, HAS TRACKED EAST-NORTHEASTWARD AT 03 KNOTS OVER THE
PAST SIX HOURS. THE CURRENT POSITION IS BASED ON RECENT SATELLITE
FIXES FROM RJTD AND PGTW, RADAR IMAGERY FROM OKINAWA AND 231713Z
MICROWAVE SATELLITE IMAGERY FROM THE AMSR2 SENSOR. THE INTENSITY OF
65 KNOTS IS CONSISTENT WITH A CONSENSUS OF SUBJECTIVE DVORAK AND
AUTOMATED INTENSITY ESTIMATES FROM MULTIPLE REPORTING AGENCIES. THE
PREVIOUS, 231200Z INTENSITY ESTIMATE WAS REVISED DOWNWARD FROM 70
KNOTS TO 60 KNOTS BASED ON A 121214Z METOP-A ASCAT DATA INDICATING NO
HIGHER THAN 50-60 KNOT WIND SPEEDS WITHIN THE SOUTHEASTERN QUADRANT
OF THE CIRCULATION. TY 09W HAS INTENSIFIED SLIGHTLY OVER THE SIX
HOURS SINCE THEN, WHILE CHURNING SLOWLY EAST-NORTHEASTWARD ALONG THE
PERIPHERY OF A DEEP-LAYERED STEERING RIDGE TO THE SOUTHEAST. DEEP
CONVECTIVE BANDING HAS PERSISTED AND EXPANDED OVER THE CIRCULATION,
PARTICULARLY WITHIN THE EASTERN SEMICIRCLE. TY 09W IS SITUATED WITHIN
AN AREA OF LOW (10-15 KNOTS) VERTICAL WIND SHEAR (VWS), VERY WARM
(29-30C) SEA SURFACE TEMPERATURES (SSTS) AND FAVORABLE RADIAL
DIFFLUENCE ALOFT.
3. FORECAST REASONING.
   A. EXTRATROPICAL TRANSITION IS NOW EXPECTED TO OCCUR IN THE
EXTENDED FORECAST PERIOD PRIOR TO DISSIPATION. FORECAST INTENSITIES
IN THE NEAR-TERM ARE SLIGHTLY LOW DUE TO THE UPDATED INTENSITY
ANALYSIS, AND FORECAST INTENSITIES AFTER TAU 48 ARE ALSO A BIT LOWER
DUE TO ANTICIPATED MID-LATITUDE TROUGH INTERACTION AND RAPID
WEAKENING OVER LAND. OTHERWISE, THERE IS NO CHANGE TO THE FORECAST
PHILOSOPHY SINCE THE PREVIOUS PROGNOSTIC REASONING MESSAGE.
   B. TY 09W WILL CONTINUE TO TRACK GENERALLY NORTHEASTWARD THROUGH
TAU 12 AS IT O FOLLOWS THE FLOW ASSOCIATED WITH THE STEERING RIDGE
POSITIONED TO THE SOUTHEAST. STEADY TO RAPID INTENSIFICATION IS
ANTICIPATED DUE TO FAVORABLE VWS, SSTS AND UPPER-LEVEL OUTFLOW. AFTER
TAU 12, A BUILDING SUBTROPICAL RIDGE TO THE EAST IS EXPECTED TO TAKE
OVER AS THE DOMINANT STEERING MECHANISM, INDUCING A GENERALLY
POLEWARD TRACK INTO THE YELLOW SEA. BY TAU 72, TY 09W WILL BEGIN THE
FIRST PHASE OF EXTRATROPICAL TRANSITIONS AS IT INTERACTS WITH A
DEVELOPING MID-LATITUDE TROUGH. SIMULTANEOUS WEAKENING IS ANTICIPATED
PRIMARILY DUE TO INCREASING VWS ASSOCIATED WITH THE MID-LATITUDE
TROUGH INTERACTION. NUMERICAL MODEL GUIDANCE IS IN FAIR AGREEMENT
WITH THE OVERALL TRACK FORECAST SCENARIO, BUT THERE IS NOTEWORTHY
SPREAD BETWEEN THE WESTERNMOST CONSENSUS MEMBERS, INCLUDING THE ECMWF
MODEL, AND THE EASTERNMOST MEMBERS, INCLUDING THE GFS MODEL. NONE OF
THE AVAILABLE MODEL FORECASTS INDICATE CENTER PASSAGE OVER SOUTH
KOREA. THE MULTI-MODEL CONSENSUS HAS BEEN CONSISTENT FOR THE PAST
SEVERAL MODEL RUNS, AND THE CURRENT JTWC TRACK FORECAST IS SITUATED
NEAR THE CONSENSUS AND PREVIOUS JTWC FORECASTS WITH FAIR CONFIDENCE.
   C. AFTER TAU 72, TY 09W IS EXPECTED TO MAKE LANDFALL IN EITHER
NORTH KOREA OR NORTHEASTERN CHINA. THE SYSTEM WILL ACCELERATE
POLEWARD OVER LAND AS IT BECOMES FULLY EMBEDDED IN THE AFOREMENTIONED
MID-LATITUDE TROUGH. RAPID WEAKENING IS ANTICIPATED DUE TO UNFAVORABLE
UPPER-LEVEL CONDITIONS AND PASSAGE OVER LAND. THE SYSTEM WILL BE
FULLY EXTRATROPICAL BY TAU 96.
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