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.// NNNN NNNN