Tropical Storm ATSANI Advisory dom, 23.08.

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 17W (ATSANI) WARNING NR 36//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TYPHOON (TY) 17W (ATSANI), LOCATED APPROXIMATELY 365 NM NORTHEAST
OF IWO TO, HAS TRACKED NORTH-NORTHEASTWARD AT 07 KNOTS OVER THE
PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI)
DEPICTS A VERY LARGE SYSTEM WITH SPIRAL BANDING WRAPPING INTO A 37-
NM EYE IN THE UPPER LEVEL CLOUDS THAT NARROWS TO 13 NM IN THE LOWER
LEVELS. OVER THE PAST FEW HOURS DEEP CONVECTION HAS RE-BUILT OVER
THE WESTERN EYEWALL, AND IT IS POSSIBLE THAT TY 17W IS UNDERGOING
SLIGHT INTENSIFICATION. THE INITIAL POSITION IS BASED ON THE EYE
FEATURE IN THE MSI AS WELL AS A 230033Z METOP-B 89 GHZ MICROWAVE
EYE, 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 FAIR ENVIRONMENT
WITH MODERATE (10-15 KNOT) NORTHEASTERLY VERTICAL WIND SHEAR AND
EXCELLENT EQUATORWARD
OUTFLOW; HOWEVER, PERSISTENT DRY AIR ENTRAINMENT ALONG THE WESTERN
PERIPHERY REMAINS IN PLACE. TY 17W IS NOW 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 ACCELERATE TO THE NORTHEAST IN THE MIDLATITUDE
WESTERLY FLOW, AHEAD OF AN APPROACHING MID-LATITUDE TROUGH. BY TAU
48, SEA SURFACE TEMPERATURES WILL DROP BELOW 26 CELSIUS AND THE
SYSTEM WILL BEGIN EXTRA-TROPICAL TRANSITION (ETT). STEADY
ENVIRONMENTAL CONDITIONS THROUGH TAU 72 WILL ALLOW FOR A SLOW
WEAKENING TREND. TY 17W IS THEREFORE EXPECTED TO BE A STRONG
EXTRATROPICAL LOW BY THE END OF THE FORECAST PERIOD.
//
NNNN
NNNN