Tropical Storm NEOGURI Advisory 10月21日

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 21W (NEOGURI) WARNING
NR 018//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL STORM (TS) 21W (NEOGURI), LOCATED APPROXIMATELY 632 NM
SOUTHWEST OF YOKOSUKA, JAPAN, HAS TRACKED NORTHEASTWARD AT 22 KNOTS
OVER THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED (EIR) SATELLITE
IMAGERY SHOWS THE SYSTEM HAS BEGUN TO SHEAR NORTHEASTWARD AND
COLLAPSE AS IT MOVED UNDER THE JET STREAM AHEAD OF A DEEP
MID-LATITUDE SHORTWAVE TROUGH CURRENTLY TRANSITING EASTWARD IN THE
EAST CHINA SEA, A POSITIVE INDICATION THAT EXTRA-TROPICAL TRANSITION
(ETT) HAS COMMENCED. THE INITIAL POSITION IS PLACED WITH HIGH
CONFIDENCE BASED ON A DEFINED CIRCULATION FEATURE IN THE COMPOSITE
RADAR LOOP FROM JMA THAT LINED UP WELL WITH A HOOK FEATURE IN THE
201620Z ATMS MICROWAVE PASS. THE INITIAL INTENSITY OF 60KTS IS BASED
ON OVERALL ASSESSMENT OF AGENCY AND OBJECTIVE DVORAK ESTIMATES
RANGING FROM T3.0/45KTS TO T4.0/60KTS AND CONSISTENT WITH THE
DEGRADED EIR SIGNATURE. UPPER LEVEL ANALYSIS INDICATES THE CYCLONE
HAS DRIFTED INTO VERY STRONG (40-50KT) VERTICAL WIND SHEAR (VWS),
ALBEIT OFFSET BY ROBUST POLEWARD OUTFLOW. TS 21W IS TRACKING ON THE
POLEWARD SIDE OF THE SUBTROPICAL RIDGE (STR) TO THE EAST.
3. FORECAST REASONING.
   A. THERE IS NO SIGNIFICANT CHANGE TO THE FORECAST PHILOSOPHY FROM
THE PREVIOUS PROGNOSTIC REASONING MESSAGE.
   B. TS 21W IS FORECAST TO ACCELERATE NORTHEASTWARD OFF THE
SOUTHEAST COAST OF JAPAN AND BY TAU 48 WILL BE SOUTHEAST OF NORTHERN
HONSHU. VWS IS EXPECTED TO INCREASE EVEN MORE (> 65KTS) AND BY TAU
24, WILL COMPLETE ETT AND TRANSFORM INTO A COLD-CORE LOW WITH AN
EXPANDING, STRONG GALE-FORCE WIND FIELD EMBEDDED IN THE BAROCLINIC
ZONE. CONSEQUENTLY, THE LOW LEVEL CIRCULATION CENTER WILL BE NEBULOUS
AND DIFFICULT TO PINPOINT DURING AND AFTER ETT. MODEL GUIDANCE HAS
REMAINED WIDELY ERRATIC WITH SEVERAL MODELS HAVING SIGNIFICANT
PROBLEMS TRACKING THE VORTEX AS IT TRACKS INSIDE THE BAROCLINIC ZONE.
OVERALL, THERE IS LOW CONFIDENCE IN THE JTWC FORECAST TRACK.//
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