WDPN31 PGTW 090300
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 13W (FENGSHEN) WARNING 
NR 09//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL STORM (TS) 13W (FENGSHEN), LOCATED APPROXIMATELY 220 NM 
SOUTHEAST OF YOKOSUKA, JAPAN, HAS TRACKED EAST-NORTHEASTWARD AT 20 
KNOTS OVER THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED (EIR) 
SATELLITE IMAGERY AND MULTISPECTRAL IMAGERY (MSI) DEPICT CURVED 
BANDING OVER THE NORTHERN SIDE OF THE SYSTEM WRAPPING INTO A DEFINED 
LLCC. EIR AND MSI INDICATES THAT THE LLCC IS BEGINNING TO DECOUPLE 
FROM THE UPPER LEVELS. A 082131Z SSMIS IMAGE AND A 082120Z CORIOLIS 
IMAGE REVEAL A SIGNIFICANT DELTA RAIN REGION ON THE NORTHEASTERN 
PERIPHERY OF THE SYSTEM INDICATIVE OF WARM FRONTOGENESIS. THE 
CURRENT POSITION IS BASED ON THE EIR AND MSI ANIMATION WITH HIGH 
CONFIDENCE. THE INITIAL INTENSITY OF 60 KNOTS IS BASED ON DVORAK 
CURRENT INTENSITY ESTIMATES. THE UPPER-LEVEL ANALYSIS CONTINUES TO 
SHOW GOOD POLEWARD OUTFLOW DUE TO A MID-LEVEL JET TO THE NORTHEAST 
OF THE SYSTEM, WHICH OFFSETS THE HIGH LEVELS (50 TO 60 KNOTS) OF 
VERTICAL WIND SHEAR. TS 13W CONTINUES TO TRACK ALONG THE NORTHERN 
PERIPHERY OF THE SUBTROPICAL RIDGE (STR) AND IS EMBEDDED IN A MID-
LATITUDE TROUGH NORTH OF THE SYSTEM.
3. FORECAST REASONING.
   A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS 
PROGNOSTIC REASONING MESSAGE.
   B. TS 13W IS FORECAST TO ACCELERATE WITHIN THE MID-LATITUDE 
WESTERLIES THROUGHOUT THE FORECAST PERIOD AS IT CONTINUES TO UNDERGO 
EXTRATROPICAL TRANSITION (ETT). INDICATION OF WARMING OF THE LOWER 
LEVELS BASED ON AN AMSU CROSS SECTION SHOWS THE SYSTEM BECOMING 
BAROCLINIC AND DEVELOPING A WARM FRONTAL PATTERN. FENGSHEN WILL 
COMPLETE ETT BY TAU 24. MODELS ARE IN VERY GOOD AGREEMENT, LENDING 
TO HIGH CONFIDENCE IN THE JTWC FORECAST.//
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