Tropical Storm ATSANI Advisory Cts, 22.08.

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 17W (ATSANI) WARNING NR 31//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TYPHOON (TY) 17W (ATSANI), LOCATED APPROXIMATELY 237 NM EAST-
NORTHEAST OF IWO TO, HAS TRACKED NORTH-NORTHWESTWARD AT 08 KNOTS
OVER THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED SATELLITE
IMAGERY SHOWS A WEAKENING CONVECTIVE STRUCTURE WITH DRY AIR
PENETRATING THE NORTHWESTERN EYEWALL. THE SYSTEM HAS MAINTAINED A 12
NM EYE, WHICH SUPPORTS THE CURRENT POSITION WITH HIGH CONFIDENCE.
MOST OF THE REMAINING CONVECTION IS CONFINED TO THE SOUTHERN
PERIPHERY WHICH IS BEING AIDED BY A ROBUST EQUATORWARD OUTFLOW. A
211738Z SSMI 85GHZ MICROWAVE IMAGE SHOWS A MUCH LARGER MICROWAVE EYE
FEATURE WITH AN ERODING EYEWALL. THE CURRENT INTENSITY HAS BEEN
LOWERED TO 90 KNOTS BASED ON DECREASING DVORAK INTENSITY ESTIMATES
FROM ALL AGENCIES AND REFLECTS THE WEAKENING CONVECTIVE STRUCTURE.
ENVIRONMENTAL CONDITIONS ARE MARGINAL DUE TO THE STRONG SUBSIDENCE
AND DRY AIR ALONG THE NORTHERN AND WESTERN PERIPHERIES; HOWEVER, SEA
SURFACE TEMPERATURES REMAIN FAVORABLE. TY 17W IS ROUNDING THE
SOUTHWESTERN 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 ROUND THE WESTERN PERIPHERY OF THE
DEEP LAYERED STR AND TURN POLEWARD. BY TAU 36, TY ATSANI WILL BEGIN
TO ACCELERATE NORTHEASTWARD IN FRONT OF AN APPROACHING MID-LATITUDE
TROUGH. ENVIRONMENTAL CONDITIONS WILL REMAIN MOSTLY UNCHANGED
THROUGH TAU 72, CREATING A SLOW WEAKENING TREND. BY TAU 72, SEA
SURFACE TEMPERATURES WILL DROP BELOW 26 CELSIUS AND THE SYSTEM WILL
BEGIN EXTRA-TROPICAL TRANSITION (ETT).
   C. IN THE EXTENDED FORECAST, TY 17W WILL CONTINUE TO ACCELERATE
NORTHEASTWARD AND EMBED FURTHER INTO THE WEAK BAROCLINIC ZONE. BY
THE END OF THE FORECAST PERIOD, TY ATSANI WILL SLOW AS IT GETS
ENVELOPED BY THE MID-LATITUDE TROUGH AND IS FORECAST TO COMPLETE ETT
AS A STRONG COLD-CORE LOW. DYNAMIC MODEL GUIDANCE REMAINS IN TIGHT
AGREEMENT LENDING HIGH CONFIDENCE IN THE JTWC FORECAST TRACK.//
NNNN
NNNN