WDPN32 PGTW 231500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 17W (ATSANI) WARNING NR 38//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TYPHOON (TY) 17W (ATSANI), LOCATED APPROXIMATELY 447 NM SOUTHEAST OF
YOKOSUKA, JAPAN, HAS TRACKED NORTHEASTWARD AT 07 KNOTS OVER THE PAST
SIX HOURS. ANIMATED ENHANCED INFRARED SATELLITE IMAGERY (EIR) SHOWS
THE SYSTEM THAT HAS BEGAN TO WEAKEN AS SPIRAL BANDING WRAPPING INTO A
RAGGED 18-NM EYE HAVE BECOME MORE SHALLOW AND LOOSE. THE INITIAL
POSITION IS BASED ON THE EYE FEATURE IN THE EIR AND ON THE 231055Z
AMSU-B MICROWAVE PASS. THE INITIAL INTENSITY OF 75 KNOTS IS BASED ON
AN OVERALL ASSESSMENT OF DVORAK ESTIMATES FROM ALL REPORTING
AGENCIES. UPPER LEVEL ANALYSIS SHOWS A MARGINAL ENVIRONMENT WITH
LIGHT TO MODERATE (10-15 KNOT) VWS AND GOOD RADIAL OUTFLOW. HOWEVER,
PERSISTENT DRY AIR ENTRAINMENT FROM THE WESTERN PERIPHERY PERSISTS.
TY 17W IS TRACKING ALONG THE NORTHWESTERN PERIPHERY OF THE
DEEP-LAYERED SUB-TROPICAL RIDGE (STR) LOCATED TO THE EAST.
3. FORECAST REASONING.
   A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS 
PROGNOSTIC REASONING MESSAGE.
   B. TY 17W WILL CONTINUE TO TRACK NORTHEASTWARD DEEPER IN THE
MID-LATITUDE WESTERLY FLOW. BY TAU 36, SEA SURFACE TEMPERATURES WILL
DROP BELOW 26 CELSIUS AND THE SYSTEM WILL BEGIN EXTRA-TROPICAL
TRANSITION (ETT). STEADY ENVIRONMENTAL CONDITIONS WILL ALLOW FOR A
SLOW WEAKENING TREND. TY 17W IS THEREFORE EXPECTED TO BECOME A STRONG
GALE-FORCE COLD CORE LOW BY THE END OF THE FORECAST PERIOD.//
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