Tropical Storm GONI Advisory 20.08.

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 16W (GONI) WARNING NR 28//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TYPHOON (TY) 16W (GONI), LOCATED APPROXIMATELY 504 NM SOUTH-
SOUTHWEST OF KADENA AB, HAS TRACKED WEST-NORTHWESTWARD AT 07 KNOTS
OVER THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED SATELLITE
IMAGERY DEPICTS A 22-NM ROUND EYE, WHICH PROVIDES GOOD CONFIDENCE IN
THE CURRENT POSITION. A 201806Z NOAA-19 89GHZ IMAGE DEPICTS AN
ERODING EYEWALL OVER THE NORTHERN SEMI-CIRCLE WITH TIGHTLY-CURVED
CONVECTIVE BANDING. UPPER-LEVEL ANALYSIS INDICATES NEAR-RADIAL
OUTFLOW WITH WEAK CONVERGENT FLOW AND MODERATE NORTHERLY VERTICAL
WIND SHEAR OVER THE NORTHERN PERIPHERY OF THE SYSTEM. THE CURRENT
INTENSITY IS ASSESSED AT 105 KNOTS BASED ON A DVORAK CURRENT
INTENSITY ESTIMATES OF T5.5 (102 KNOTS) FROM PGTW. TY 16W IS
TRACKING ALONG THE SOUTHWESTERN PERIPHERY OF A NARROW, EAST-WEST
ORIENTED STR TO THE NORTH. THE STR IS RELATIVELY WEAK DUE TO THE
PRESENCE OF THE TWO TROPICAL CYCLONES AS WELL AS A STRONG
SUBTROPICAL WESTERLY JET PERSISTING OVER THE KOREAN PENINSULA AND
JAPAN.
3. FORECAST REASONING.
   A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS
PROGNOSTIC REASONING MESSAGE.
   B. WITHIN THE NEXT 12 HOURS, TY 16W IS FORECAST TO SLOW AS
THE STR STEERING INFLUENCE TO THE NORTH WEAKENS. BASED ON THE RECENT
500MB ANALYSES, THE STR TO THE NORTH IS WEAKENING RAPIDLY AS THE
WESTERLIES STRENGTHEN AND THE ANTICYCLONE OVER CHINA RETROGRADES.
THE 20/12Z 500MB ANALYSIS SHOWS A BROAD WEAKENESS BETWEEN THE
WESTERN AND EASTERN RIDGES. AFTER TAU 12, THE WESTERN BRANCH OF THE
STR OVER CHINA IS EXPECTED TO WEAKEN FURTHER AND RECEDE WESTWARD,
THEREFORE, TRACK MOTION THROUGH TAU 24 IS EXPECTED TO SLOW FURTHER
WITH POSSIBLE QUASI-STATIONARY MOTION DUE TO THE WEAK STEERING
ENVIRONMENT. DYNAMIC MODEL GUIDANCE IS UNANIMOUS IN DEPICTING A
SIGNIFICANT SLOW DOWN WITH MAJOR DIFFERENCES IN THE TIMING OF THE
POLEWARD TURN, THEREFORE, THERE IS UNCERTAINTY IN THIS PHASE OF THE
SYSTEM. AFTER TAU 12, THE STR IS FORECAST TO RE-BUILD EAST OF THE
SYSTEM PROVIDING A POLEWARD ORIENTED TRACK, WHICH SHOULD ALLOW THE
SYSTEM TO SLOWLY TRACK NORTHWARD. AVAILABLE MODEL TRACKERS AND
ENSEMBLE GUIDANCE SUPPORT THIS NORTHWARD TRACK. TY 16W SHOULD WEAKEN
GRADUALLY THROUGH THE FORECAST PERIOD DUE TO LAND INTERACTION AND
INCREASED UPPER-LEVEL CONVERGENCE ASSOCIATED WITH THE UPPER-LEVEL
SUBTROPICAL WESTERLIES ENCROACHING ON THE WESTERN PERIPHERY OF THE
SYSTEM.
   C. IN THE EXTENDED PERIOD, TY 16W WILL TURN NORTHEASTWARD AS IT
TRACKS ALONG THE NORTHWESTERN PERIPHERY OF THE STR. DYNAMIC GUIDANCE
IS IN POOR AGREEMENT, THEREFORE, THERE IS LOW OVERALL CONFIDENCE IN
THE JTWC FORECAST TRACK.//
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