Tropical Storm GUCHOL Advisory Pzt, 18.06.

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 05W (GUCHOL) WARNING NR 28//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
TYPHOON (TY) 05W (GUCHOL), LOCATED APPROXIMATELY 350 NM SOUTH OF
KADENA AB, OKINAWA, HAS TRACKED NORTHWARD AT 11 KNOTS OVER THE PAST
SIX HOURS. TY 05W HAS RECENTLY BEEN DOWNGRADED FROM SUPER TYPHOON
STATUS TO TYPHOON. ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY
SHOWS THE SYSTEM HAS STARTED TO SHOW SIGNS OF WEAKENING AS THE EYE
DIAMETER HAS SLOWLY DECREASED OVER THE PAST SIX HOURS FROM 15 NM TO
10 NM AND IS BECOMING MORE RAGGED. THE DEEPEST CONVECTION REMAINS ON
THE SOUTHERN HALF OF THE SYSTEM, BUT CONVECTION ALONG THE
NORTHWESTERN QUADRANT HAS STARTED TO WEAKEN SLIGHTLY OVER THE PAST
SIX HOURS. THE EYEWALL REPLACEMENT CYCLE (ERC) HAS FINISHED WITH NO
IDENTIFIABLE IMPACT TO THE OVERALL INTENSITY. TY 05W HAS SHIFTED TO A
NORTHWARD TRACK AT THE WARNING TIME, AND SINCE ISSUING WARNING NUMBER
28, EIR IMAGERY IS INDICATING A SLIGHT TURN TO THE EAST-NORTHEAST AS
TY 05W APPEARS TO HAVE STARTED TO TRACK AROUND THE DEEP-LAYERED
SUBTROPICAL RIDGE (STR) AXIS. THE CURRENT POSITION IS BASED ON THE
EYE IN EIR AND AGREES WITH PGTW FIX. THE CURRENT INTENSITY IS
SLIGHTLY DECREASED TO 125 KNOTS BASED ON A 6.0/6.5 DVORAK FIX FROM
PGTW AND A 5.0/5.5 FROM RJTD BOTH SHOWING A SLIGHT WEAKENING TREND.
THIS AGREES WITH THE OBSERVED WEAKENING TREND NOTED IN EIR.
UPPER-LEVEL ANALYSIS INDICATES THE MESOSCALE ANTICYCLONE REMAINS
SLIGHTLY DISPLACED LOW-LEVEL CIRCULATION CENTER (LLCC). THIS FEATURE
CONTINUES TO VENT THE SYSTEM ALONG THE EQUATORWARD OUTFLOW CHANNEL.
THE POLEWARD CHANNEL HAS YET TO TAP INTO THE STRONG UPPER-LEVEL JET.
3. FORECAST REASONING.
   A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS
PROGNOSTIC REASONING MESSAGE.
   B. TY 05W IS EXPECTED TO CONTINUE TRACKING TO THE EAST-NORTHEAST
AROUND THE NORTHWESTERN PERIPHERY OF THE STEERING STR. AN UPPER-LEVEL
TROUGH LOCATED OVER EASTERN CHINA IS EXPECTED TO MODIFY THE STR
FURTHER AS TY 05W TRACKS TOWARDS JAPAN. MODEL GUIDANCE IS IN VERY
GOOD AGREEMENT THROUGH TAU 36, SHOWING TY 05W GRADUALLY WEAKENING AS
THE OVERALL ENVIRONMENT DETERIORATES.
THE WEAKENING TREND WILL BEGIN SLOWLY AS VERTICAL WIND SHEAR (VWS)
INCREASES AS TY 05W APPROACHES THE MID-LATITUDE FRONTAL BOUNDARY
ASSOCIATED WITH A LOW PRESSURE CIRCULATION CURRENTLY LOCATED OVER
NORTHEAST CHINA. AS THE LOW MOVES TOWARDS THE SEA OF JAPAN BETWEEN
TAU 24 AND 36, THE VWS IS EXPECTED TO FURTHER WEAKEN TY 05W. SEA
SURFACE TEMPERATURES (SSTS) HAVE BEEN FAVORABLE TO THIS POINT;
HOWEVER, THEY WILL SLOWLY DECREASE OVER THE NEXT 12 TO 24 HOURS,
GOING FROM 29 CELSIUS TO APPROXIMATELY 24 TO 26 CELSIUS BY TAU 24.
BEYOND TAU 24 SSTS REMAIN VERY UNFAVORABLE. THE MAJOR CONCERN WITH
THE FORECAST IS BEYOND TAU 36. THE FORECAST KEEPS THE TRACK TO THE
WEST OF TOKYO AS THE SYSTEM UNDERGOES EXTRA-TROPICAL TRANSITION
(ETT). MODEL GUIDANCE CONTINUES TO INDICATE A TRACK OVER KYOTO INTO
THE SEA OF JAPAN. THE THOUGHT PROCESS FOR THE FORECAST IS THAT MODEL
GUIDANCE IS TRACKING TOWARDS THE MID-LEVEL VORTICITY FIELDS, WHILE
THE LLCC IS EXPECTED TO TRACK ALONG THE STATIONARY FRONTAL BOUNDARY
LOCATED ALONG COASTAL JAPAN. LAND EFFECTS ON THE LLCC DURING THE ETT
PROCESS WILL CREATE A VERY DISORGANIZED STRUCTURE BETWEEN TAU 48 AND
72. THERE IS HIGH CONFIDENCE IN THE FORECAST TRACK THROUGH TAU 36,
BUT DECREASES TO LOW BEYOND TAU 36 AS THE FORECAST TRACK DIFFERS FROM
THE MAJORITY OF MODEL GUIDANCE WITHIN THE CONSENSUS.//
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