Tropical Storm KROSA Advisory Mon Aug 12

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 11W (KROSA) WARNING NR
026//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL STORM (TS) 11W (KROSA), LOCATED APPROXIMATELY 664 NM
SOUTH-SOUTHEAST OF IWAKUNI, JAPAN, HAS TRACKED WEST-NORTHWESTWARD AT
08 KNOTS OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE
IMAGERY DEPICTS A LARGE EXPOSED CORE, APPROXIMATELY 140-150NM
DIAMETER, WITH A WELL-DEFINED LOW-LEVEL CIRCULATION CENTER AND
LIMITED DEEP CONVECTIVE BANDING. AN 112141Z WINDSAT 37GHZ IMAGE
CONTINUES TO DEPICT SHALLOW CONVECTIVE BANDING WRAPPING TIGHTLY INTO
A BROAD LLCC WITH SOME WEAKER INNER BANDING. OVERALL, THERE IS GOOD
CONFIDENCE IN THE CURRENT POSITION. IN GENERAL, DVORAK INTENSITY
ESTIMATES ARE TOO LOW BECAUSE THE CONVECTIVE STRUCTURE IS UNUSUALLY
BROAD DUE TO A PERSISTENT, COMPACT UPPER LOW OVER THE CORE. HOWEVER,
A RECENT SMAP IMAGE (110825Z) INDICATES 55-60 KNOT WINDS DISPLACED
OUTWARD FROM THE CENTER AND RECENT AMSU INTENSITY ESTIMATES RANGE
FROM 48-63 KNOTS, WHICH SUPPORT THE CURRENT INTENSITY ASSESSMENT OF
55 KNOTS. WITH THE EXCEPTION OF THE SUBSIDENCE OVER THE LARGE CORE,
ENVIRONMENTAL CONDITIONS REMAIN FAVORABLE WITH LOW VERTICAL WIND
SHEAR AND WARM SST (28-29C). TS 11W IS TRACKING SLOWLY ALONG THE
SOUTHERN FLANK OF A SUBTROPICAL RIDGE (STR) POSITIONED OVER JAPAN.
3. FORECAST REASONING.
   A. THERE IS NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE
PREVIOUS PROGNOSTIC REASONING MESSAGE. THE PEAK INTENSITY IS STILL
EXPECTED TO BE 70 KNOTS BUT WILL OCCUR NEAR TAU 60, JUST PRIOR TO
LANDFALL AT TAU 72.
   B. OVER THE NEXT 48 HOURS, TS 11W WILL TRACK NORTHWESTWARD ALONG
THE SOUTHERN PERIPHERY OF THE STR, HOWEVER, BY TAU 72 THE SYSTEM
SHOULD TURN POLEWARD AS IT BEGINS TO RECURVE ALONG THE SOUTHWEST
PERIPHERY OF THE STR. THE UPPER LOW OVER THE CENTER IS FORECAST TO
WEAKEN AFTER TAU 24, WHICH WILL ALLOW THE SYSTEM TO GRADUALLY
INTENSIFY AS IT APPROACHES WESTERN JAPAN. AFTER TAU 48, POLEWARD
OUTFLOW SHOULD IMPROVE AS 11W TAPS INTO THE DEEP MIDLATITUDE
SHORTWAVE TROUGH DIGGING OVER THE EAST CHINA SEA, WHICH WILL ALLOW
THE SYSTEM TO INTENSIFY TO TYPHOON STRENGTH. NUMERICAL MODEL
GUIDANCE REMAINS IN TIGHT AGREEMENT WITH THE MODELS SPREAD FROM
EASTERN KYUSHU TO EASTERN SHIKOKU. ADDITIONALLY, THE ECMWF
ENSEMBLE'S STRIKE PROBABILITY PRODUCT IS ALSO INDICATING HIGH
PROBABILITY OF THE SYSTEM TRACKING IN THIS SAME REGION. THEREFORE,
THERE IS HIGH CONFIDENCE IN THIS PORTION OF THE JTWC FORECAST TRACK.
   C. AFTER TAU 72, TS KROSA WILL TRACK NORTH-NORTHEASTWARD OVER
WESTERN HONSHU AND THE EAST SEA THROUGH TAU 96. TS 11W REMAINS A
VERY LARGE (7-8 DEGREE DIAMETER) SYSTEM AND IS EXPECTED TO REMAIN
VERY LARGE WITH AN EXPANSIVE AREA OF GALE-FORCE WINDS. DUE TO THE
COMPLEXITY OF THE UPPER-LEVEL FLOW OVER THE SYSTEM, THERE IS SOME
UNCERTAINTY IN THE JTWC INTENSITY FORECAST. TS 11W IS FORECAST TO
BEGIN EXTRA-TROPICAL TRANSITION (ETT) OVER THE EAST SEA BY TAU 96.
IT WILL COMPLETE ETT BY TAU 120 AS IT ACCELERATES NORTH-
NORTHEASTWARD RETAINING AN EXPANSIVE AREA OF GALE-FORCE WINDS WHICH
COULD IMPACT NORTHERN JAPAN. OVERALL, THERE IS HIGH CONFIDENCE IN
THE JTWC FORECAST TRACK.//
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