WDPN31 PGTW 081500
MSGID/GENADMIN/NAVMARFCSTCEN PEARL HARBOR HI/JTWC//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 17W (KULAP) WARNING NR 
06//
RMKS/
1. FOR METEOROLOGISTS.
2. 12 HOUR SUMMARY AND ANALYSIS.
   A. TROPICAL STORM (TS) 17W (KULAP) LOCATED APPROXIMATELY 250 NM 
EAST OF KADENA AB, JAPAN, HAS TRACKED NORTHWESTWARD AT 15 KNOTS OVER 
THE PAST SIX HOURS. ANIMATED INFRARED SATELLITE IMAGERY SHOWS A 
WELL-DEFINED, FULLY EXPOSED LOW LEVEL CIRCULATION CENTER (LLCC) WITH 
THE DEEP CONVECTION SHEARED 170 NM TO THE SOUTH. THE INITIAL 
INTENSITY IS BASED ON A 080848Z WINDSAT PASS DEPICTING STRONG 30- TO 
35-KNOT WINDS ALONG THE EASTERN PERIPHERY OF THE LLCC. UPPER LEVEL 
ANALYSIS INDICATES THE SYSTEM IS LOCATED IN AN AREA OF HIGH VERTICAL 
WIND SHEAR (20 TO 30 KNOTS) AND DIRECTLY BENEATH A TROPICAL UPPER 
TROPOSPHERIC TROUGH CAUSING SUBSIDENCE ALOFT. ADDITIONALLY, A 
081110Z SSMIS MICROWAVE IMAGE DEPICTS DRY AIR WRAPPING ALONG THE 
WESTERN PERIPHERY OF THE LLCC. A 080700Z CIRA AMSU CROSS-SECTION 
SHOWS A WARM CORE ANOMALY ONLY NEAR THE SURFACE WITH A COLD CORE 
ANOMALY IN THE UPPER LEVELS. TS 17W IS CURRENTLY TRACKING ALONG THE 
SOUTHWESTERN PERIPHERY OF A LOW- TO MID-LEVEL SUBTROPICAL STEERING 
RIDGE.
   A. THE CURRENT FORECAST PHILOSOPHY HAS CHANGED IN THAT TS 17W IS 
EXPECTED TO WEAKEN MORE RAPIDLY THAN PREVIOUSLY FORECAST DUE TO THE 
CURRENT AND PREDICTED UNFAVORABLE UPPER LEVEL ENVIRONMENT.
   B. TS 17W IS EXPECTED TO CONTINUE TRACKING NORTHWESTWARD OVER THE 
NEXT 36 TO 48 HOURS, WHEN AN APPROACHING MID-LATITUDE TROUGH WILL 
BEGIN TO WEAKEN THE STEERING RIDGE AND ALLOW THE SYSTEM TO TURN 
POLEWARD. BY TAU 48, TS 17W SHOULD WEAKEN DUE TO COOLER SEA SURFACE 
TEMPERATURES AND SIGNIFICANTLY INCREASED VERTICAL WIND SHEAR, 
ASSOCIATED WITH THE MID-LATITUDE TROUGH. BY TAU 72 THE SYSTEM IS 
EXPECTED TO DISSIPATE AS A SIGNIFICANT TROPICAL CYCLONE. NUMERICAL 
MODEL GUIDANCE HAS COME INTO BETTER AGREEMENT WITH DISSIPATION PRIOR 
TO MAKING LANDFALL OVER KOREA EXCEPT FOR GFDN, WHICH SHARPLY 
RECURVES THE SYSTEM INTO THE WESTERLIES. NOGAPS REMAINS THE WESTERN 
OUTLIER AS IT MAINTAINS A STRONGER SUBTROPICAL RIDGE. THIS FORECAST 
IS TO THE LEFT OF MODEL CONSENSUS TO ACCOUNT FOR THE UNLIKELY GFDN 
FAST RECURVATURE SCENARIO.//
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