Tropical Storm BAVI Advisory Mon Aug 24

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 09W (BAVI) WARNING NR
013//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TYPHOON 09W (BAVI), LOCATED APPROXIMATELY 412 NM SOUTH-
SOUTHWEST OF CHINHAE, SOUTH KOREA, HAS TRACKED NORTH-
NORTHWESTWARD AT 07 KNOTS OVER THE PAST SIX HOURS. ANIMATED
ENHANCED INFRARED (EIR) SATELLITE IMAGERY DEPICTS A COMPACT
SYSTEM WITH DENSE, SUSTAINED CONVECTION WRAPPING AROUND A
TRANSIENT EYE WHICH HAS DEVELOPED AND FILLED OVER THE PAST 6
HOURS. THE CURRENT POSITION IS PLACED WITH HIGH CONFIDENCE BASED
ON THE EYE FEATURE PRESENT IN THE EIR AND COMPOSITE RADAR LOOPS
AND ON THE MICROWAVE EYE FEATURE PRESENT IN A 241003Z SSMIS 97
GHZ IMAGE. THE CURRENT INTENSITY IS PLACED WITH FAIR CONFIDENCE
BASED ON A PGTW DVORAK CURRENT INTENSITY ESTIMATE OF T5.0(90KTS).
THE STRONG CONVECTIVE SIGNATURE AND EYE DEVELOPMENT IN THE EIR
LOOP OVER THE PAST 6 HOURS SUPPORT AN INTENSITY CLOSER TO THE
HIGHER END OF THE DVORAK INTENSITY ESTIMATE. TY BAVI HAS
CONTINUED TO TRACK ALONG THE WESTERN PERIPHERY OF A BUILDING
SUBTROPICAL RIDGE POSITIONED TO THE EAST AND HAS CONTINUED TO
INTENSIFY OVER THE PAST SIX HOURS DUE TO THE CONTINUED FAVORABLE
ENVIRONMENT OF LOW (10-15 KNOTS) VERTICAL WIND SHEAR (VWS), VERY
WARM (29-30C) SEA SURFACE TEMPERATURES (SSTS) AND ESTABLISHED
EQUATORWARD OUTFLOW ALOFT.
3. FORECAST REASONING.
   A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS
PROGNOSTIC REASONING MESSAGE.
   B. TY 09W WILL CONTINUE TO TRACK POLEWARD OVER THE NEXT 72
HOURS ALONG THE WESTERN PERIPHERY OF THE BUILDING SUBTROPICAL
RIDGE TO THE EAST. THE ENVIRONMENT WILL MOVE FROM FAVORABLE TO
MARGINALLY FAVORABLE OVER THE NEXT 12 HOURS DUE TO INCREASING,
MODERATE (15-25 KTS) VWS AND CONVERGENT FLOW ALONG THE NORTHERN
PERIPHERY OF THE SYSTEM. DESPITE THIS, CONTINUED VERY WARM SSTS
WILL ALLOW THE SYSTEM TO TO INTENSIFY TO 105 KTS DURING THIS
DECREASING VWS THEREAFTER ALONG WITH CONTINUED WARM SSTS WILL
ALLOW THE SYSTEM TO INTENSIFY FURTHER TO 115 KTS BY TAU 24. AS
THE SYSTEM ROUNDS THE STEERING RIDGE AND CONTINUES TO TRACK
POLEWARD, IT WILL BEGIN TO ENCOUNTER COOLING SSTS AND INCREASING
VWS, WHICH WILL LEAD TO GRADUAL WEAKENING TO 85 KTS BY TAU 48.
THEREAFTER, THE SYSTEM WILL MAKE LANDFALL OVER THE KOREAN
PENINSULA AND TRACK INLAND OVER MAINLAND CHINA. INTERACTION WITH
AN INCOMING TROUGH IN THE UPPER LEVELS AND THE UNDERLYING TERRAIN
WILL CAUSE THE SYSTEM TO WEAKEN TO 40 KTS BY TAU 72. ADDITIONALLY,
IT WILL BEGIN EXTRATROPICAL TRANSITION BY THIS TIME AS IT BECOMES
EMBEDDED IN THE BAROCLINIC ZONE. NUMERICAL MODEL TRACK SOLUTIONS
ARE IN TIGHT AGREEMENT WITH A CROSS TRACK SPREAD OF 66 NM AT TAU
48 INCREASING TO 208 NM BY TAU 72. MODEL SOLUTIONS HAVE CLUSTERED
ABOUT THE JTWC MULTI-MODEL CONSENSUS WITH GFS, NAVGEM AND UK MODELS
TO THE WEST AND JGSM, GFS ENSEMBLE AND ECMWF MODEL SOLUTIONS TO THE
EAST. NONE OF THE AVAILABLE MODEL SOLUTIONS INDICATE STORM CENTER
PASSAGE OVER SOUTH KOREA, BUT THE EASTERN GROUP DOES CARRY THE STORM
CENTER ALONG THE WESTERN SHORE. THE JTWC MULTI-MODEL CONSENSUS HAS
BEEN HIGHLY CONSISTENT FOR MULTIPLE MODEL RUNS. THE INITIAL PORTION
OF THE JTWC FORECAST TRACK IS THEREFORE PLACED WITH HIGH CONFIDENCE
AS IT IS SITUATED NEAR THE CONSENSUS AND NEAR PREVIOUS JTWC FORECAST
TRACKS.
   C. AS THE SYSTEM TRACKS OVER MAINLAND CHINA, IT WILL ACCELERATE
POLEWARD AS IT BECOMES FULLY EMBEDDED IN THE BAROCLINIC ZONE. RAPID
WEAKENING IS ANTICIPATED DUE TO UNFAVORABLE UPPER-LEVEL CONDITIONS
AND THE FRICTIONAL EFFECTS OF LAND. THE SYSTEM WILL COMPLETE
EXTRATROPICAL TRANSITION BY TAU 96 AS IT BECOMES EMBEDDED IN THE
DEEP WESTERLY FLOW ALOFT. NUMERICAL MODEL SOLUTIONS BIFURCATE AFTER
TAU 72 WITH A CROSS TRACK SPREAD > 1000 NM AT TAU 96. DESPITE
THIS HIGH DEGREE OF SPREAD IN THE FINAL PORTION OF THE FORECAST
TRACK, THERE REMAINS HIGH CONFIDENCE IN THE OVERALL JTWC FORECAST
TRACK DUE TO THE TIGHT PACKING OF MODEL SOLUTIONS OVERALL.
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