Tropical Storm GONI Advisory vie, 21-08

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 16W (GONI) WARNING NR 29//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TYPHOON (TY) 16W (GONI), LOCATED APPROXIMATELY 518 NM SOUTH-
SOUTHWEST OF KADENA AB, HAS TRACKED WESTWARD AT 05 KNOTS OVER THE
PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY DEPICTS A
CLOUD-FILLED EYE, THEREFORE, THERE IS GOOD CONFIDENCE IN THE CURRENT
POSITION. A 202314Z SSMIS IMAGE SHOWS A PARTIAL EYEWALL WITH TIGHTLY-
CURVED BANDING LOCATED PRIMARILY OVER THE SOUTHERN SEMI-CIRCLE.
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 100 KNOTS BASED ON DVORAK CURRENT INTENSITY ESTIMATES RANGING
FROM 90 TO 102 KNOTS. TY 16W IS TRACKING SLOWLY 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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