Tropical Storm ATSANI Advisory Wed Aug 19

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 17W (ATSANI) WARNING NR 17//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TYPHOON (TY) 17W (ATSANI), LOCATED APPROXIMATELY 622 NM EAST-
NORTHEAST OF ANDERSEN AFB, GUAM, HAS TRACKED WEST-NORTHWESTWARD AT 09
KNOTS OVER THE PAST SIX HOURS. RECENT ANIMATED MULTISPECTRAL
SATELLITE IMAGERY SHOWS THE SYSTEM HAS MAINTAINED OVERALL CONVECTIVE
SIGNATURE WITH TIGHTLY-CURVED BANDS WRAPPING INTO AN 18-NM DIAMETER
EYE. THE INITIAL POSITION IS BASED ON THE EYE FEATURE, ALSO EVIDENT
ON A 180551Z GPM MICROWAVE PASS, WITH HIGH CONFIDENCE. THE INITIAL
INTENSITY OF 115 KNOTS IS BASED ON CONGRUENT AND CONCENTRIC DVORAK
FIXES FROM PGTW AND RJTD. UPPER-LEVEL ANALYSIS INDICATES TY ATSANI IS
LOCATED IN A FAVORABLE ENVIRONMENT WITH LOW (05 TO 10 KNOT) VWS AND
EXCELLENT RADIAL OUTFLOW. 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. TY 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 140 BY TAU 36.
AFTER TAU 48, INCREASING VWS WILL BEGIN TO WEAKEN THE SYSTEM.
   C. TY 17W WILL CONTINUE TO TRACK NORTHWESTWARD UNDER THE STEERING
STR THROUGH TAU 96. AFTERWARD, AN UPPER-LEVEL TROUGH PASSING TO THE
NORTH WILL CAUSE A WEAKNESS IN THE STR, TURNING TY 17W SLIGHTLY
POLEWARD. CONCURRENTLY, THE COMBINED EFFECTS OF LOWER OHC VALUES AND
INCREASED VWS WILL CONTINUE TO DECAY TY ATSANI. AVAILABLE MODEL
GUIDANCE REMAINS IN TIGHT AGREEMENT LENDING HIGH CONFIDENCE IN THE
JTWC FORECAST TRACK.//
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