Tropical Storm ATSANI Advisory lun, 17-08

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 17W (ATSANI) WARNING NR 12//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TYPHOON (TY) 17W (ATSANI), LOCATED APPROXIMATELY 248 NM
NORTHWEST OF ENEWETAK, HAS TRACKED WESTWARD AT 04 KNOTS OVER THE
PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY DEPICTS A
SLOWLY CONSOLIDATING SYSTEM WITH IMPROVED CONVECTIVE BANDING AND A
37-NM RAGGED EYE. A 162041Z SSMIS IMAGE REFLECTS THE IMPROVED
ORGANIZATION AND REVEALS A 120-NM EYEWALL AND DEEP CONVECTIVE
BANDING LOCATED PRIMARILY OVER THE SOUTHERN SEMI-CIRCLE OF THE
SYSTEM. BASED ON THE EYE FEATURE, THERE IS GOOD CONFIDENCE IN THE
CURRENT POSITION. THE CURRENT INTENSITY IS ASSESSED AT 75 KNOTS
BASED ON A T4.5 DVORAK INTENSITY ESTIMATE FROM PGTW. ANIMATED WATER
VAPOR IMAGERY CONTINUES TO SHOW EXCELLENT OVERALL OUTFLOW, ENHANCED
BY A TUTT CELL NEAR THE DATELINE; HOWEVER, THE IMAGERY SUGGESTS
UPPER-LEVEL CONVERGENCE ASSOCIATED WITH THE TUTT PRESSING DOWN OVER
THE NORTHERN PERIPHERY OF THE SYSTEM. TY 17W REMAINS IN A COMPETING
STEERING ENVIRONMENT BETWEEN A WEAK NEAR-EQUATORIAL RIDGE TO THE
SOUTH AND THE STRONG STR TO THE NORTH. THIS STEERING INFLUENCE HAS
GENRALLY PRODUCED A SLOW WESTWARD TRACK.
3. FORECAST REASONING.
   A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS
PROGNOSTIC REASONING MESSAGE.
   B. TY 17W WILL CONTINUE TRACKING SLOWLY WESTWARD THROUGH TAU 12
DUE TO THE COMPETING STEERING ENVIRONMENT. BEYOND TAU 12, THE NER
WILL SHIFT TO THE EAST ALLOWING THE STR TO BECOME THE DOMINANT
STEERING INFLUENCE. THEREFORE, TY 17W WILL ACCELERATE NORTHWESTWARD
ALONG THE SOUTHWEST PRIPHERY OF THE STR. DUE TO THE BROAD NATURE OF
THE LLCC AND THE MARGINALLY-FAVORABLE ENVIRONMENT, THE SYSTEM IS
EXPECTED TO INTENSIFY AT A CLIMATOLOGICAL RATE THROUGH TAU 72.
   C. IN THE EXTENDED FORECAST PERIOD, AN APPROACHING MID-LATITUDE
SHORTWAVE TROUGH OVER THE KOREAN PENINSULA AND WESTERN JAPAN WILL
ERODE THE WESTERN PERIPHERY OF THE STR, WHICH WILL ALLOW TY 17W TO
MAINTAIN A NORTHWESTWARD TRACK TOWARD IWO TO. AVAILABLE MODEL
GUIDANCE REMAINS IN TIGHT AGREEMENT, THEREFORE, THERE IS HIGH
CONFIDENCE IN THE JTWC FORECAST TRACK. AFTER TAU 120, CURRENT
GUIDANCE SUPPORTS A RE-CURVE SCENARIO TOWARD WESTERN OR CENTRAL
JAPAN ALTHOUGH THERE IS CURRENTLY A HIGH DEGREE OF UNCERTAINTY IN
THE EXACT TIMING OF THE RE-CURVE.//
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