Tropical Storm ATSANI Advisory gio, 20.08.

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 17W (ATSANI) WARNING NR 27//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TYPHOON (TY) 17W (ATSANI), LOCATED APPROXIMATELY 325 NM EAST-
SOUTHEAST OF IWO TO, JAPAN HAS TRACKED NORTHWESTWARD AT 11 KNOTS
OVER THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED SATELLITE
IMAGERY INDICATES THAT THE SYSTEM HAS WEAKENED SLIGHTLY WITH
DECREASING DEEP CONVECTION OVER THE NORTHERN SEMI-CIRCLE; HOWEVER,
THE SYSTEM HAS MAINTAINED A 49-NM ROUND EYE. A 201622Z NOAA-19 89GHZ
IMAGE SHOWS ERODING CONVECTIVE BANDING AND EYEWALL CONVECTION OVER
THE NORTHWEST QUADRANT. OVERALL, THERE IS GOOD CONFIDENCE IN THE
CURRENT POSITION BASED ON THE EYE. UPPER-LEVEL ANALYSIS CONTINUES TO
REVEAL RADIAL OUTFLOW AND LOW VWS. THE CURRENT INTENSITY IS ASSESSED
AT 115 KNOTS BASED ON DVORAK CURRENT INTENSITY ESTIMATES OF 115
KNOTS. TY 17W IS TRACKING ALONG THE WESTERN PERIPHERY OF THE DEEP-
LAYERED STR.
3. FORECAST REASONING.
   A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS
PROGNOSTIC REASONING MESSAGE.
   B. TY 17W WILL CONTINUE TO TRACK NORTHWESTWARD TO NORTHWARD
THROUGH TAU 48 UNDER THE STEERING INFLUENCE OF THE AFOREMENTIONED
STR. AFTER TAU 48, TY 17W WILL TURN NORTH-NORTHEASTWARD TO
NORTHEASTWARD AS IT ROUNDS THE NORTHWEST PERIPHERY OF THE STR AND
BEGINS TO ACCELERATE INTO THE WESTERLIES. UPPER-LEVEL CONDITIONS ARE
EXPECTED TO SLOWLY BECOME LESS FAVORABLE WITH INCREASING VWS.
ADDITIONALLY, TY 17W WILL ENCOUNTER MARGINAL SST, THEREFORE, GRADUAL
WEAKENING IS FORECAST THROUGH TAU 72.
   C. IN THE EXTENDED PERIOD, TY 17W WILL TRACK NORTHEASTWARD AND
WILL BEGIN TO INTERACT WITH A WEAK BAROCLINIC ZONE, WHICH WILL SERVE
TO FURTHER WEAKEN THE CONVECTIVE STRUCTURE. THE SYSTEM SHOULD REMAIN
AT STORM-FORCE STRENGTH AFTER TAU 96 DESPITE THE RAPIDLY DWINDLING
DEEP CONVECTION. AVAILABLE MODEL GUIDANCE REMAINS IN TIGHT AGREEMENT
LENDING HIGH CONFIDENCE IN THE JTWC FORECAST TRACK.//
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