Tropical Storm BAVI Advisory 8月21日

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL DEPRESSION 09W (NINE)
WARNING NR 001//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL DEPRESSION (TD) 09W (NINE), LOCATED APPROXIMATELY 408 NM
SOUTHWEST OF KADENA AB, OKINAWA, HAS TRACKED NORTHWARD AT 10 KNOTS
OVER THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED SATELLITE
IMAGERY AND ANIMATED RADAR IMAGERY DEPICT A CONSOLIDATING SYSTEM
WITH IMPROVED CONVECTIVE BANDING OVER THE SOUTHERN AND EASTERN
SEMICIRCLES. A 211041Z SSMIS 91GHZ COMPOSITE MICROWAVE IMAGE REVEALS
SHALLOW BANDING WRAPPING INTO A PARTIALLY-EXPOSED, BROAD LOW-LEVEL
CIRCULATION CENTER WITH FORMATIVE DEEP CONVECTIVE BANDING, WHICH
SUPPORTS THE INITIAL POSITION WITH FAIR CONFIDENCE. A 211229Z ASCAT-
B IMAGE INDICATES A SWATH OF 25 TO 35 KNOT WINDS OVER THE EASTERN
SEMICIRCLE; HOWEVER, THE 30-35 KNOT WINDS ARE ISOLATED AND ARE
ASSOCIATED WITH A SMALL BURST OF DEEP CONVECTION OVER THE EASTERN
QUADRANT. SURFACE OBSERVATIONS FROM LAN YU (59567), APPROXIMATELY
40NM WEST OF THE CENTER, ARE NORTHEASTERLY AT 16 KNOTS WITH AN SLP
VALUE OF 1006.9MB, WHICH SUGGESTS WEAKER WINDS OVER THE WESTERN
SEMICIRCLE. THEREFORE, THE INITIAL INTENSITY IS HELD CONSERVATIVELY
AT 25 KNOTS WHICH IS SUPPORTED BY DVORAK ESTIMATES OF T1.0-1.5 (25
KNOTS) FROM PGTW, KNES AND RJTD. ENVIRONMENTAL CONDITIONS ARE
CONDUCIVE FOR FURTHER DEVELOPMENT WITH LOW TO MODERATE (10-20 KNOTS)
VERTICAL WIND SHEAR (VWS), GOOD EQUATORWARD OUTFLOW AND ENHANCED
POLEWARD OUTFLOW ASSOCIATED WITH AN UPPER-LOW TO THE NORTHEAST AS
WELL AS WARM SST VALUES (30C) AND HIGH OCEAN HEAT CONTENT VALUES
REFLECTING A DEEP, WARM POOL OF WATER. TD 09W IS TRACKING GENERALLY
POLEWARD ALONG THE WESTERN PERIPHERY OF A SUBTROPICAL RIDGE (STR) TO
THE EAST WITH A WEAK EXTENSION OF THE STR ALSO POSITIONED NORTH OF
THE SYSTEM.
3. FORECAST REASONING.
   A. THIS IS THE INITIAL PROGNOSTIC REASONING MESSAGE FOR THIS
SYSTEM AND SETS THE FORECAST PHILOSOPHY.
   B. THE WEAK STR EXTENSION POSITIONED NORTH OF TD 09W IS EXPECTED
TO ERODE OVER THE NEXT DAY AS WESTERLIES ASSOCIATED WITH A SHORTWAVE
TROUGH DIG OVER THE EAST CHINA SEA, WHICH WILL ALLOW THE STEERING
STR TO REORIENT AND PRODUCE A SLOW NORTHEASTWARD TRACK MOTION FROM
TAU 24 TO TAU 72. THE TROUGH WILL ALSO ENHANCE POLEWARD OUTFLOW AND
ALLOW THE SYSTEM TO INTENSIFY RAPIDLY TO 100 KNOTS BY TAU 72.
DYNAMIC MODEL GUIDANCE IS IN FAIR AGREEMENT WITH A SPREAD OF 110NM
AT TAU 48 AND 125NM AT TAU 72.
   C. IN THE EXTENDED PERIOD, THE AFOREMENTIONED SHORTWAVE TROUGH IS
FORECAST TO PROPAGATE EASTWARD WITH THE STR BUILDING OVER WESTERN
JAPAN, WHICH WILL PRODUCE A NORTHWARD TRACK TOWARD SOUTH KOREA.
ENVIRONMENTAL CONDITIONS WILL GRADUALLY DEGRADE AFTER THE SYSTEM
PEAKS AT TAU 96 AT 105 KNOTS WITH MORE SIGNIFICANT WEAKENING AS THE
SYSTEM BEGINS TO INTERACT WITH THE KOREAN PENINSULA AND ENCOUNTERS
INCREASING VWS. MODEL GUIDANCE REMAINS IN FAIR AGREEMENT WITH
UNCERTAINTY IN THE EXACT LANDFALL LOCATION. OVERALL, THERE IS
MODERATE CONFIDENCE IN THE JTWC FORECAST TRACK.//
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