Tropical Storm CHAN-HOM Advisory Fri Jul 10

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 09W (CHAN-HOM) WARNING NR 41//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TYPHOON (TY) 09W (CHAN-HOM), LOCATED APPROXIMATELY 630 NM SOUTH-
SOUTHWEST OF YONGSAN AIN, SOUTH KOREA, HAS TRACKED NORTHWESTWARD
AT 09 KNOTS OVER THE PAST SIX HOURS. ANIMATED INFRARED (IR)
SATELLITE IMAGERY DEPICTS A LARGE, WELL-ORGANIZED SYSTEM WITH
EXTENSIVE SPIRAL BANDING WRAPPING INTO A 12-NM EYE, WHICH LENDS GOOD
CONFIDENCE TO THE CURRENT POSITION. HOWEVER, IR IMAGERY SHOWS A
GRADUAL WEAKENING TREND WITH WARMING CONVECTIVE TOPS AND DIMINISHING
DEEP CONVECTIVE BANDING OVER THE NORTHERN SEMI-CIRCLE. A 101044Z
SSMIS 91 GHZ IMAGE CONTINUES TO HINT AT A POSSIBLE EYEWALL
REPLACEMENT CYCLE (ERC) AND SHOWS A COMPACT INNER EYEWALL SURROUNDED
BY AN OUTER WALL AND EXTENSIVE CONVECTIVE BANDING WRAPPING TIGHTLY
INTO THE SYSTEM. BASED ON A SLIGHT WEAKENING TREND DUE TO ERC, THE
CURRENT INTENSITY HAS BEEN DECREASED TO 100 KNOTS BASED ON THE LOWER
END OF DVORAK CURRENT INTENSITY ESTIMATES RANGING FROM 102 TO
115 KNOTS. UPPER-LEVEL ANALYSIS INDICATES FAVORABLE UPPER-LEVEL
CONDITIONS WITH GOOD DIFFLUENCE ALOFT. TY 09W IS TRACKING ALONG THE
SOUTHWESTERN PERIPHERY OF THE DEEP-LAYERED STR TO THE NORTH.
3. FORECAST REASONING.
   A. THERE IS NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE
PREVIOUS PROGNOSTIC REASONING MESSAGE.
   B. TY 09W IS FORECAST TO CONTINUE TRACKING NORTHWESTWARD UNDER
THE STEERING INFLUENCE OF THE STR THROUGH TAU 24. THE SYSTEM IS
FORECAST TO WEAKEN DUE TO ERC AND LAND INTERACTION AS IT RE-CURVES
POLEWARD ALONG THE EAST COAST OF CHINA. AFTER TAU 36, THE SYSTEM
WILL TRACK OVER THE WEST SEA BUT IS FORECAST TO WEAKEN RAPIDLY DUE
TO COLD SST (21 TO 23C) AND STRONG VWS. THEREFORE, TY 09W WILL
LIKELY WEAKEN TO MINIMAL TROPICAL STORM STRENGTH BY TAU 72, WHICH
SHOULD PRODUCE GALE-FORCE WINDS ALONG THE WEST COAST OF SOUTH KOREA.
AVAILABLE DYNAMIC GUIDANCE IS IN FAIR AGREEMENT ON THE GENERAL TRACK
BUT POOR AGREEMENT ON THE TRACK SPEEDS. THE GFS, GFS ENSEMBLE AND
HWRF INDICATE MUCH FASTER SPEEDS WITH THE TAU 72 POSITION OVER THE
VICINITY OF NORTHEASTERN NORTH KOREA. ECMWF, EGRR AND NAVGEM ARE
SLOWER WITH TAU 72 POSITIONS WEST OF SEOUL. JGSM AND THE JGSM
ENSEMBLE ARE IN BETWEEN THESE TWO EXTREMES. BASED ON THE LARGE
DIFFERENCES IN TRACK SPEED AND THE EVOLVING SYNOPTIC PATTERN, THERE
IS LOW CONFIDENCE IN THE JTWC TRACK FORECAST AFTER TAU 36. DUE TO
THE WEAK BAROCLINIC ZONE AND WESTERLIES, THE TRACK SPEEDS SHOULD
REMAIN 10 TO 15 KNOTS AS THE SYSTEM TRACKS ACROSS THE KOREAN
PENINSULA.
   C. TY CHAN-HOM IS NOT EXPECTED TO UNDERGO EXTRA-TROPICAL
TRANSITION DUE TO THE WEAK NATURE OF THE BAROCLINIC ZONE AND IS,
INSTEAD, FORECAST TO DISSIPATE OVER KOREA BY TAU 96. DUE TO THE
LARGE SPREAD IN THE NUMERICAL GUIDANCE AND UNCERTAINTY IN THE LATER
TAUS, THERE IS LOW CONFIDENCE IN THE JTWC TRACK FORECAST, WHICH IS
POSITIONED CLOSE TO BUT SLIGHTLY FASTER THAN THE MULTI-MODEL
CONSENSUS.//
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