Tropical Storm GUCHOL Advisory Mon Jun 18

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 05W (GUCHOL) WARNING NR 29//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
TYPHOON (TY) 05W (GUCHOL), LOCATED APPROXIMATELY 265 NM SOUTH OF
KADENA AB, OKINAWA, HAS TRACKED NORTH-NORTHEASTWARD AT 14 KNOTS OVER
THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY SHOWS
THE EYEWALL HAS BEEN DETERIORATING OVER THE PAST SIX HOURS. DEEP
CONVECTION OBSERVED WITHIN THE ENHANCED INFRARED (EIR) SATELLITE
IMAGERY HAS DIMINISHED ALONG THE SOUTHEASTERN QUADRANT OF THE LOW
LEVEL CIRCULATION CENTER (LLCC). A SERIES OF MICROWAVE IMAGES,
INCLUDING THE MOST RECENT 172150Z SSMIS PASS, SUPPORT THE BREAKDOWN
OF DEEP CONVECTION. THE INITIAL INTENSITY HAS BEEN ADJUSTED TO 115
KNOTS TO REFLECT THIS OBSERVED WEAKENING TREND AND IS SUPPORTED BY A
5.5/6.5 DVORAK FIX FROM PGTW. THE INITIAL POSITION IS BASED ON THE
PRESENCE OF THE CLOUD FILLED EYE FEATURE AND THE FIX BY PGTW. UPPER-
LEVEL ANALYSIS INDICATES THE MESOSCALE ANTICYCLONE REMAINS SLIGHTLY
DISPLACED FROM THE LOW-LEVEL CIRCULATION CENTER (LLCC). THIS FEATURE
CONTINUES TO VENT THE SYSTEM ALONG THE EQUATORWARD OUTFLOW CHANNEL.
TY 05W HAS RECENTLY SHIFTED TO AN EAST-NORTHEASTWARD TRACK AROUND
THE AXIS OF THE DEEP SUBTROPICAL RIDGE (STR).
3. FORECAST REASONING.
   A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS
PROGNOSTIC REASONING MESSAGE.
   B. TY 05W IS EXPECTED TO TRACK EAST-NORTHEAST AROUND THE
NORTHWESTERN PERIPHERY OF THE STEERING STR. AN UPPER-LEVEL TROUGH
LOCATED OVER EASTERN CHINA IS FORECAST TO MODIFY THE STR FURTHER AS
TY 05W TRACKS TOWARDS JAPAN. MODEL GUIDANCE IS IN 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 ALONG THE EASTERN COAST OF JAPAN. AS THE
LOW THAT IS CURRENTLY LOCATED OVER NORTHEASTERN CHINA MOVES TOWARDS
THE SEA OF JAPAN, VWS WILL INCREASE FURTHER WEAKENING TY 05W BY TAU
36 AND BEGIN THE PROCESS OF EXTRA-TROPICAL TRANSITION (ETT). SEA
SURFACE TEMPERATURES (SSTS) SLOWLY STARTED TO DECREASE AND WILL
CONTINUE ON THIS TREND THROUGHOUT THE FORECAST PERIOD. WITHIN THE
NEXT 24 HOURS SSTS WILL DROP BELOW FAVORABLE CONDITIONS FOR
DEVELOPMENT, LEADING TO FURTHER WEAKENING OF THE LLCC. THE FORECAST
KEEPS THE TRACK TO THE WEST OF TOKYO AS THE SYSTEM COMPLETES ETT BY
TAU 48. 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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