WDPN31 PGTW 290300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 15W (TEMBIN) WARNING NR 
41//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL STORM (TS) 15W (TEMBIN), LOCATED APPROXIMATELY 600 NM 
SOUTH-SOUTHWEST OF SEOUL, SOUTH KOREA, HAS TRACKED NORTHWARD AT 12 
KNOTS OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE 
IMAGERY SHOWS THE LARGE, BROAD REGION OF DEEP CONVECTION HAS 
PERSISTED TO THE SOUTHWEST OF THE LOW LEVEL CIRCULATION CENTER 
(LLCC). THE CURRENT INTENSITY HAS BEEN DECREASED TO 45 KNOTS BASED 
ON THE WEAKENING TREND OBSERVED OVER THE PAST SIX HOURS, AND IS 
SUPPORTED BY THE 3.0/3.0 DVORAK ESTIMATE FROM PGTW. UPPER LEVEL 
ANALYSIS INDICATES TS 15W IS SLIGHTLY POLEWARD OF A SUBTROPICAL 
RIDGE (STR) AXIS THAT EXTENDS FROM CENTRAL JAPAN TO DIRECTLY OVER 
TAIWAN. THE UPPER LEVEL REFLECTION OF THE DEEP STR INDICATES WINDS 
FROM THE EAST ARE PRODUCING LOW TO MODERATE LEVELS OF VERTICAL WIND 
SHEAR (VWS) ALONG THE EASTERN AND NORTHEASTERN PORTIONS OF THE LLCC. 
TS 15W IS CURRENTLY TRACKING AROUND THE MID-LEVEL REFLECTION OF THE 
STR WHICH HAS BECOME THE DOMINANT STEERING MECHANISM.
3. FORECAST REASONING.
   A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS 
PROGNOSTIC REASONING MESSAGE.
   B. TS 15W IS FORECAST TO TRACK NORTH-NORTHEASTWARD THROUGH TAU 24 
UNDER THE INFLUENCE OF THE STR. THIS IS NOT EXPECTED TO SHIFT UNTIL 
THE SYSTEM MAKES LANDFALL AROUND TAU 30 SHIFTING TO A MORE EASTWARD 
TRACK AS THE STR SHIFTS IN RESPONSE TO THE REMNANTS OF EXTRATROPICAL 
STORM 16W (BOLAVEN) TRACKING TO THE NORTH OF THE STR. TS 15W WILL 
STRUGGLE AS IT SLOWLY WEAKENS AS IT TRACKS POLEWARD INTO A LESS 
FAVORABLE ENVIRONMENT WITH INCREASING VWS AND DECREASING SEA SURFACE 
TEMPERATURES. BY TAU 36 INCREASING INTERACTION WITH AN APPROACHING 
MID-LATITUDE TROUGH WILL BEGIN THE EXTRATROPICAL TRANSITION PROCESS. 
FRICTIONAL EFFECTS AND CONTINUED INTERACTION WITH THE TROUGH WILL 
LEAD TO COMPLETE EXTRATROPICAL SYSTEM BY TAU 48. MODEL GUIDANCE IS 
IN GOOD AGREEMENT WITH THE TRACK, BUT APPEARS TO SLOW THE SYSTEM AS 
IT APPROACHES THE KOREAN PENINSULA. MODEL FIELDS APPEAR TO INDICATE 
THE LLCC IS LOST WITHIN THE APPROACHING TROUGH, THUS LOSE THE 
ABILITY TO TRACK THE REMNANTS OF THE LLCC. BASED ON THIS ASSESSMENT, 
THE CURRENT FORECAST KEEPS THE TRACK FASTER THAN THE CONSENSUS OF 
MODEL GUIDANCE, BUT STILL HAS HIGH CONFIDENCE.//
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