Tropical Storm ATSANI Advisory Paz, 23.08.

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 17W (ATSANI) WARNING NR 35//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TYPHOON (TY) 17W (ATSANI), LOCATED APPROXIMATELY 192 NM SOUTHEAST
OF CHICHI JIMA, HAS TRACKED NORTH-NORTHEASTWARD AT 06 KNOTS OVER THE
PAST SIX HOURS. ANIMATED ENHANCED INFRARED SATELLITE IMAGERY (EIR)
DEPICTS A VERY LARGE SYSTEM WITH SPIRAL BANDING WRAPPING INTO A 38-
NM EYE. A 221114Z ASCAT PASS PROVIDES A GOOD ESTIMATE OF THE
EXTENSIVE 35-KNOT WIND FIELD. THE INITIAL POSITION IS BASED ON THE
EYE FEATURE IN THE EIR AS WELL AS IN A 221721Z SSMI 37GHZ IMAGE WITH
HIGH CONFIDENCE. THE INITIAL INTENSITY OF 80 KNOTS IS BASED ON AN
OVERALL ASSESSMENT OF DVORAK ESTIMATES FROM ALL REPORTING AGENCIES.
UPPER LEVEL ANALYSIS SHOWS A MARGINAL ENVIRONMENT WITH MODERATE (20
KNOT) NORTHEASTERLY VERTICAL WIND SHEAR AND GOOD EQUATORWARD
OUTFLOW; HOWEVER, DRY AIR ENTRAINMENT ALONG THE WESTERN PERIPHERY IS
INHIBITING INTENSIFICATION. TY 17W IS NOW TRACKING ALONG THE NORTH
WESTERN 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 ACCELERATE TO THE NORTHEAST AS IT BECOMES EMBEDDED
IN THE MIDLATITUDE WESTERLIES, AHEAD OF AN APPROACHING MID-LATITUDE
TROUGH.
ENVIRONMENTAL CONDITIONS WILL REMAIN MOSTLY UNCHANGED THROUGH TAU 72,
CREATING A SLOW WEAKENING TREND. BY TAU 48, SEA SURFACE TEMPERATURES
WILL DROP BELOW 26 CELSIUS AND THE SYSTEM WILL BEGIN EXTRA-TROPICAL
TRANSITION (ETT).
   C. TY 17W WILL COMPLETE ETT, BECOMING A STRONG COLD CORE LOW BY
TAU 96 AND POSSIBLY SOONER. AFTER TAU 72, THE STEERING FLOW IS
FORECAST TO BREAK DOWN LEADING TO A SLOW AND POSSIBLY ERRATIC TRACK
AS DEPICTED IN THE MAJORITY OF DYNAMICAL MODELS. THE REASONABLY GOOD
AREEMENT AMONG TRACK GUIDANDE AIDS LENDS HIGH CONFIDENCE TO THE JTWC
FORECAST TRACK.//
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