Tropical Storm NEOGURI Advisory 10月20日

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 21W (NEOGURI) WARNING
NR 014//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TYPHOON 21W (NEOGURI), LOCATED APPROXIMATELY 241 NM SOUTH OF
KADENA AB, OKINAWA, JAPAN, HAS TRACKED NORTH-NORTHEASTWARD AT 06
KNOTS OVER THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED SATELLITE
IMAGERY DEPICTS A COMPACT SYSTEM WITH AN 8NM EYE, WHICH SUPPORTS THE
CURRENT POSITION WITH GOOD CONFIDENCE. THE CURRENT INTENSITY IS
ASSESSED AT 95 KNOTS BASED ON AVERAGING DVORAK INTENSITY ESTIMATES OF
5.0 FROM RJTD AND 5.5 FROM PGTW. UPPER-LEVEL ANALYSIS INDICATES
MODERATE (25 KNOTS) VERTICAL WIND SHEAR (VWS) OFFSET BY ROBUST
POLEWARD OUTFLOW INTO A DEEP UPPER-LEVEL TROUGH TO THE NORTH. SST
VALUES OF 27-28C REMAIN CONDUCIVE. THE SYSTEM IS TRACKING ALONG THE
WESTERN PERIPHERY OF A SUBTROPICAL RIDGE (STR) POSITIONED TO THE
EAST-NORTHEAST.
3. FORECAST REASONING.
   A. THERE IS NO SIGNIFICANT CHANGE TO THE FORECAST PHILOSOPHY FROM
THE PREVIOUS PROGNOSTIC REASONING MESSAGE.
   B. TY 21W IS FORECAST TO CONTINUE TRACKING NORTH-NORTHEASTWARD
THROUGH TAU 36, TRANSITIONING TO A NORTHEASTERLY TRACK THROUGH TAU
72. BY TAU 24, THE SYSTEM WILL BEGIN INTERACTING WITH A DEEP
SHORTWAVE TROUGH POSITIONED OVER THE EAST CHINA SEA AND BEGIN
EXTRA-TROPICAL TRANSITION (ETT). THE SYSTEM IS CURRENTLY ANTICIPATED
TO BE AT THE MAXIMUM INTENSITY AND WILL WEAKEN SLOWLY OVER THE NEXT
12 HOURS TO 90 KNOTS. AFTER TAU 12, VWS IS EXPECTED TO INCREASE
SLIGHTLY TO 30-35 KNOTS AND WILL INCREASE SIGNIFICANTLY BY TAU 36 TO
45-50 KNOTS, WHICH WILL WEAKEN TY 21W. AFTER TAU 36, TY 21W WILL
ENCOUNTER INCREASING VWS (45-70 KNOTS) AS IT BECOMES EMBEDDED WITHIN
THE MIDLATITUDE WESTERLIES AND SHOULD COMPLETE ETT BY TAU 48. BY TAU
72, TY 21W WILL BE REDUCES TO 40KTS. DUE TO THE COMPLEX SYNOPTIC
ENVIRONMENT, LARGE SPREAD IN MODEL SOLUTIONS AND EXTRA-TROPICAL
NATURE OF THE SYSTEM, THERE IS HIGH UNCERTAINTY IN THE EXACT POSITION
OF THE CENTER AS THE SYSTEM APPROACHES CENTRAL HONSHU. THE MODEL AIDS
HAVE STARTED TRENDING SLIGHTLY NORTH OF PREVIOUS FORECAST TRACKS
PUTTING THE EXTRA-TROPICAL SYSTEM CLOSER TO HONSHU. THE GLOBAL MODELS
CONSISTENTLY FORECAST A STRONG JET TO REMAIN ENTRENCHED OVER JAPAN
AND JUST TO THE SOUTH OF HONSHU, WHICH SHOULD SUPPORT A STRONG
BAROCLINIC, COLD-CORE LOW AFTER TAU 48.
   C. BEYOND TAU 72, TY 21W IS EXPECTED TO ACCELERATE NORTHEASTWARD
AS IT TRACKS UNDER A SOUTHWESTERLY JET. THIS 40-KNOT EXTRA-TROPICAL
LOW IS EXPECTED TO WEAKEN SLIGHTLY TO 35 KNOTS BY TAU 96, ALBEIT WITH
A VERY LARGE WIND FIELD, AS IT TRACKS EAST OF HONSHU. DUE TO THE
LARGE SPREAD IN MODEL SOLUTIONS, THERE IS LOW CONFIDENCE IN THE JTWC
TRACK FORECAST.//
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