Tropical Storm ATSANI Advisory wo, 19-08

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR SUPER TYPHOON 17W (ATSANI) WARNING NR
22//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   SUPER TYPHOON (STY) 17W (ATSANI), LOCATED APPROXIMATELY 637 NM EAST-
SOUTHEAST OF IWO TO, JAPAN, HAS TRACKED NORTHWESTWARD AT 07 KNOTS OVER
THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY
SHOWS THE SYSTEM HAS BECOME MORE SYMMETRIC AND DEEP WITH FEEDER BANDS
WRAPPING TIGHTER INTO AN EXPANDED 34-NM DIAMETER EYE. THE EIR LOOP
ALSO SHOWS A SECONDARY EYE IS BEGINNING TO FORM WITHIN THE PRIMARY
EYE. THIS EYE WALL REPLACEMENT CYCLE IS CAPTURED IN A 190910Z F18
MICROWAVE PASS. THE INITIAL POSITION IS BASED ON THE EYE FEATURE WITH
HIGH CONFIDENCE. THE INITIAL INTENSITY OF 140 KNOTS IS BASED ON AN
OVERALL ASSESSMENT OF DVORAK INTENSITY ESTIMATES FROM ALL REPORTING
AGENCIES AND REFLECTS THE IMPROVED STATE OF THE CYCLONE. UPPER-LEVEL
ANALYSIS INDICATES THE SYSTEM IS LOCATED IN A FAVORABLE ENVIRONMENT
WITH LOW (05 TO 10 KNOT) VWS AND EXCELLENT RADIAL OUTFLOW, AS EVIDENT
ON ANIMATED WATER VAPOR IMAGERY. THE CYCLONE IS TRACKING ALONG THE
SOUTHWESTERN PERIPHERY OF A STR TO THE NORTHEAST.
3. FORECAST REASONING.
   A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS
PROGNOSTIC REASONING MESSAGE.
   B. STY 17W WILL REMAIN ON A NORTHWESTWARD TRAJECTORY THROUGH TAU
72 UNDER THE STEERING STR. VERY FAVORABLE ENVIRONMENTAL AND UPPER-
LEVEL CONDITIONS ARE EXPECTED TO PERSIST ALLOWING THE SYSTEM TO
FURTHER INTENSIFY LEADING TO A PEAK INTENSITY OF 145 OVER THE NEXT 24
HOURS. AFTERWARDS, INCREASING VWS WILL BEGIN TO WEAKEN THE SYSTEM.
   C. IN THE LATER TAUS, AN UPPER-LEVEL TROUGH PASSING TO THE NORTH
WILL CAUSE A WEAKNESS IN THE STR, TURNING STY ATSANI MORE POLEWARD.
CONCURRENTLY, THE COMBINED EFFECTS OF LOWER OHC VALUES AND INCREASED
VWS WILL FURTHER ERODE THE SYSTEM. BY TAU 120, THE SYSTEM WILL ENTER
THE COLD BAROCLINIC ZONE AND BEGIN EXTRA-TROPICAL TRANSITION.
AVAILABLE MODEL GUIDANCE REMAINS IN TIGHT AGREEMENT LENDING HIGH
CONFIDENCE IN THE JTWC FORECAST TRACK.//
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