WDPN31 PGTW 271500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR SUPER TYPHOON 18W (JELAWAT) WARNING NR 
29//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   SUPER TYPHOON (STY) 18W (JELAWAT), LOCATED APPROXIMATELY 390 NM 
SOUTH-SOUTHWEST OF KADENA AIR BASE, OKINAWA, JAPAN, HAS TRACKED 
NORTH-NORTHWESTWARD AT 09 KNOTS OVER THE PAST SIX HOURS. ANIMATED 
INFRARED SATELLITE IMAGERY CONTINUES TO INDICATE AN INTENSE 
SYSTEM WITH A 36-NM ROUND EYE. A 270928Z SSMIS IMAGE SHOWS MULTIPLE 
TIGHTLY-CURVED SPIRAL BANDS WRAPPING INTO A SYMMETRIC EYEWALL. 
ANIMATED WATER VAPOR IMAGERY CONTINUES TO INDICATE EXCELLENT RADIAL 
OUTFLOW ENHANCED BY THE SUBTROPICAL TROUGH POSITIONED JUST EAST OF 
HONSHU; HOWEVER, THERE IS SOME INCREASED PRESSURE OVER THE NORTHWEST 
PERIPHERY DUE TO INCREASING NORTHWESTERLY FLOW. THERE IS GOOD 
CONFIDENCE IN THE INITIAL POSITION AND RECENT MOTION BASED ON THE 
EYE FIXES. THE INITIAL INTENSITY OF 135 KNOTS IS BASED ON AN AVERAGE 
OF DVORAK ESTIMATES RANGING FROM 127 TO 140 KNOTS AND IS CONSISTENT 
WITH CIMSS OBJECTIVE DVORAK ESTIMATES. THE 27/00Z 500MB ANALYSIS 
SHOWS THAT THE SUBTROPICAL RIDGE (STR) TO THE NORTH OF 18W HAS 
CONTINUED TO ERODE DUE TO PERSISTENT TROUGHING OVER EASTERN CHINA 
AND THE YELLOW SEA. THEREFORE, STY 18W HAS BEGUN TO TURN MORE 
POLEWARD OVER THE PAST SIX HOURS.
3. FORECAST REASONING.
   A. NO CHANGE TO THE FORECAST PHILOSOPHY; HOWEVER, TRACK SPEEDS 
HAVE BEEN INCREASED AFTER TAU 48 DUE TO A SIGNIFICANT SHIFT IN 
DYNAMIC MODEL TRACK SPEEDS THAT IS MORE REALISTIC.
   B. STY 18W IS TRACKING ALONG THE WESTERN PERIPHERY OF THE STR AND 
IS FORECAST TO TURN NORTHWARD THEN NORTHEASTWARD BY TAU 24 AS THE 
APPROACHING MIDLATITUDE SHORTWAVE TROUGH DEEPENS OVER THE EAST CHINA 
SEA. DYNAMIC MODEL GUIDANCE IS IN VERY TIGHT AGREEMENT THROUGH TAU 
72 WITH A NOTEWORTHY 60-NM SPREAD AT TAU 48. ADDITIONALLY, MODEL 
GUIDANCE IS CONSISTENT ON TRACK SPEEDS AS WELL. MODEL GUIDANCE IS 
CURRENTLY CLUSTERED OVER OKINAWA AND THE JTWC FORECAST REMAINS 
CONSISTENT WITH PREVIOUS FORECASTS WITH SOME UNCERTAINTY IN THE 
EXACT TRACK DUE TO THE SHARP TURN THAT IS FORECAST WITHIN THE NEXT 
24 HOURS. REGARDLESS OF THE EXACT TRACK NEAR OKINAWA, STY 18W IS A 
300-NM DIAMETER SYSTEM WITH A LARGE EYE AND EYEWALL AND WILL 
MAINTAIN 100+ KNOT WINDS THROUGH TAU 48 DUE TO CONTINUED FAVORABLE 
ENVIRONMENTAL CONDITIONS. AFTER TAU 48, MODEL GUIDANCE REMAINS 
TIGHTLY CLUSTERED BUT BEGINS TO DIVERGE SIGNIFICANTLY ON TRACK 
SPEEDS. OVERALL, MODEL GUIDANCE IS TRENDING FASTER. THERE IS HIGH 
CONFIDENCE IN THE FORECAST TRACK THROUGH TAU 48 BUT LOW CONFIDENCE 
THEREAFTER.
   C. IN THE EXTENDED PERIOD, MODEL GUIDANCE DIVERGES DUE TO 
ERRONEOUS INTERACTION WITH THE MIDLATITUDE TROUGH. THIS HAS RESULTED 
IN ERRATIC TRACK GUIDANCE WITH CYCLONICALLY-SHAPED TRACKS OVER AND 
ACROSS THE JAPAN ALPS. THE JTWC FORECAST TRACK REMAINS CONSISTENT 
WITH A MORE REALISTIC TRACK OVER THE SOUTH CENTRAL PORTION OF 
HONSHU. THIS TRACK IS POSITIONED TO THE RIGHT OF THE MULTI-MODEL 
CONSENSUS TRACK. STY 18W IS FORECAST TO BEGIN EXTRA-TROPICAL 
TRANSITION (ETT) AFTER TAU 48 AND WILL COMPLETE ETT BY TAU 96.//
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