Tropical Storm NEOGURI Advisory Mon Oct 21

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 21W (NEOGURI) WARNING
NR 016//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TYPHOON (TY) 21W (NEOGURI), LOCATED APPROXIMATELY 142 NM SOUTH-
SOUTHEAST OF KADENA AB, OKINAWA, HAS TRACKED NORTHEASTWARD AT 14
KNOTS OVER THE PAST SIX HOURS. TY 21W IS CURRENTLY INTERACTING WITH
A DEEP MIDLATITUDE SHORTWAVE TROUGH SITUATED OVER THE EAST CHINA
SEA, THEREFORE, EXTRA-TROPICAL TRANSITION (ETT) HAS COMMENCED. THE
20/00Z NAZE SOUNDING (47909) INDICATES A SOUTH-SOUTHWESTERLY JET
WITH 75-85 KNOTS AT 300-200MB, WHICH IS PRODUCING VERY STRONG (40-50
KNOTS) VERTICAL WIND SHEAR (VWS) AND ROBUST POLEWARD OUTFLOW. AS
REVEALED IN RADAR IMAGERY, THE SYSTEM HAS RETAINED AN EYE DESPITE
THE BULK OF THE DEEP CONVECTION SHEARING TO THE NORTH-NORTHEAST.
THERE IS GOOD CONFIDENCE IN THE CURRENT POSITION BASED ON THE RADAR
IMAGERY AND CORRESPONDING RJTD RADAR FIXES. THE CURRENT INTENSITY IS
ASSESSED CONSERVATIVELY AT 80 KNOTS BASED ON THE CONVECTIVE
STRUCTURE AND DVORAK INTENSITY ESTIMATES OF 4.0/5.0 FROM RJTD AND
PGTW. AFTER A SHORT-TERM NORTHEASTWARD TRAJECTORY OVER THE PAST SIX
HOURS, RADAR IMAGERY NOW INDICATES THAT TY 21W IS TRACKING NORTH-
NORTHEASTWARD AGAIN. FORTUNATELY, THE COMPACT SYSTEM REMAINS WELL TO
THE SOUTHEAST OF OKINAWA, WHICH IS REPORTING SUSTAINED WINDS OF 10-
15 KNOTS WITH GUSTS UP TO 25 KNOTS.
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 TRACK NORTH-NORTHEASTWARD THROUGH TAU 24
WITHIN THE STRONG SOUTH-SOUTHWESTERLY FLOW BETWEEN THE
AFOREMENTIONED SHORTWAVE TROUGH AND THE STR POSITIONED TO THE EAST.
VWS IS EXPECTED TO INCREASE SIGNIFICANTLY (> 65 KNOTS) BY TAU 36 AS
THE SYSTEM TRACKS UNDER THE JET AND RAPIDLY COMPLETES ETT.
CONSEQUENTLY, RAPID WEAKENING IS ANTICIPATED. NUMERICAL MODEL
GUIDANCE IS IN GOOD AGREEMENT ONLY THROUGH TAU 36 THEN DIVERGES WITH
INCREASING UNCERTAINTY IN THE CENTER POSITION AND FORECAST TRACK AS
THE SYSTEM GAINS FRONTAL CHARACTERISTICS AND THE CENTER BROADENS.
AFTER THE SYSTEM TRANSITIONS TO AN EXTRA-TROPICAL, COLD-CORE LOW,
THE CURRENT JTWC FORECAST IS EXTENDED TO 72 HOURS AS A COURTESY TO
ASSETS IN JAPAN DUE TO THE PRESENCE OF GALE-FORCE WINDS THROUGHOUT
THE FORECAST PERIOD. IN GENERAL, THE LATEST RUN OF MODEL GUIDANCE
HAS IMPROVED SIGNIFICANTLY WITH A MORE COHESIVE DEPICTION OF THE
SYSTEM TRACKING SOUTH AND EAST OF HONSHU. OVERALL, THERE IS LOW
CONFIDENCE IN THE JTWC FORECAST TRACK.//
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