WDPN32 PGTW 181500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 17W (ATSANI) WARNING NR 18//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TYPHOON (TY) 17W (ATSANI), LOCATED APPROXIMATELY 606 NM EAST-
NORTHEAST OF ANDERSEN AFB, GUAM, HAS TRACKED NORTHWESTWARD AT 08
KNOTS OVER THE PAST SIX HOURS. RECENT ANIMATED ENHANCED INFRARED
SATELLITE IMAGERY SHOWS THE SYSTEM HAS MAINTAINED OVERALL CONVECTIVE
SIGNATURE WITH SLIGHTLY COOLER TOPS AND CURVED BANDS WRAPPING TIGHTER
INTO A 16-NM DIAMETER EYE. THE INITIAL POSITION IS BASED ON THE EYE
FEATURE, ALSO EVIDENT ON A 181054ZZ AMSU-B MICROWAVE PASS, WITH HIGH
CONFIDENCE. THE INITIAL INTENSITY OF 120 KNOTS IS HELD SLIGHTLY
HIGHER THAN THE CONGRUENT DVORAK FIXES FROM PGTW, KNES, AND RJTD TO
REFLECT THE SLIGHT INTENSIFICATION. 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.//
NNNN