Tropical Storm BAVI Advisory Tue Aug 25

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 09W (BAVI) WARNING NR
012//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TYPHOON (TY) 09W (BAVI), LOCATED APPROXIMATELY 450 NM SOUTH-
SOUTHWEST OF CHINHAE, SOUTH KOREA, HAS TRACKED NORTHEASTWARD AT 07
KNOTS OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE
IMAGERY DEPICTS A COMPACT SYSTEM WITH DENSE, SUSTAINED CONVECTION
WRAPPING AROUND AN IRREGULAR EYE 27 NM IN DIAMETER. THE CURRENT
POSITION IS PLACED WITH HIGH CONFIDENCE BASED ON THE EYE FEATURE
PRESENT IN THE MSI AND COMPOSITE RADAR LOOPS. THE CURRENT INTENSITY
IS PLACED WITH FAIR CONFIDENCE BETWEEN MULTIAGENCY DVORAK CURRENT
INTENSITY ESTIMATES OF T4.0 (65 KTS, RJTD AND RCTP) AND T4.5 (77
KTS, PGTW). THE STRONG CONVECTIVE SIGNATURE AND EYE DEVELOPMENT IN
THE MSI LOOP SUPPORT AN INTENSITY CLOSER TO THE HIGHER END OF
SUBJECTIVE DVORAK VALUES. TY 09W 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. RAPID INTENSIFICATION IS ANTICIPATED THROUGH TAU 36 DUE TO
WARM SSTS (30 CELSIUS) AND LOW VWS (10-15 KTS), COUPLED WITH THE WELL
ESTABLISHED EQUATORWARD OUTFLOW ALOFT WHICH WILL STRENGTHEN THE
SYSTEM TO 105 KTS BY TAU 24 AND A PEAK INTENSITY OF 110 KTS BY TAU 36.
AFTER THIS TIME, INCREASING VWS WILL CAUSE THE SYSTEM TO WEAKEN
SLIGHTLY BY TAU 48 TO AN INTENSITY OF 105 KTS. THEREAFTER, THE SYSTEM
WILL CONTINUE TO TRACK POLEWARD AS IT BEGINS TO INTERACT WITH THE
BAROCLINIC ZONE OVER THE YELLOW SEA. TY BAVI WILL MAKE LAND FALL
OVER THE KOREAN PENINSULA AT THIS TIME AND BEGIN EXTRATROPICAL
TRANSITION AT TAU 72. NUMERICAL MODEL TRACK SOLUTIONS ARE IN TIGHT
AGREEMENT WITH A CROSS TRACK SPREAD OF 100 NM AT TAU 48 INCREASING
SLIGHTLY TO 130 NM BY TAU 72. MODEL SOLUTIONS HAVE OSCILLATED ABOUT
THE JTWC MULTI-MODEL CONSENSUS WITH GFS, NAVGEM AND UK MODELS TO THE
WEST AND JGSM AND ECMWF MODELS TO THE EAST. NONE OF THE AVAILABLE
MODEL FORECASTS 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 VERY 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 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 DIVERGE GREATLY
AFTER TAU 72, WITH A TOTAL SPREAD OF 365 NM BY TAU 120. DESPITE THIS
HIGH DEGREE OF SPREAD IN THE FINAL PORTION OF THE FORECAST TRACK,
THERE STILL REMAINS HIGH CONFIDENCE IN THE OVERALL JTWC FORECAST
TRACK DUE TO THE TIGHT PACKING OF MODEL SOLUTIONS OVERALL.
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