Tropical Storm FENGSHEN Advisory Tue Sep 09

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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