Tropical Storm NEOGURI Advisory Sun Oct 20

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 21W (NEOGURI) WARNING
NR 012//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TYPHOON (TY) 21W (NEOGURI), LOCATED APPROXIMATELY 295 NM SOUTH OF
KADENA AB, OKINAWA, HAS TRACKED NORTHWESTWARD AT 07 KNOTS OVER THE
PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY DEPICTS A
COMPACT SYSTEM WITH A RAGGED, FORMATIVE 5NM EYE. A 190447Z AMSR2
89GHZ MICROWAVE IMAGE INDICATES A 30NM DIAMETER CORE WITH A SMALL
MICROWAVE EYE FEATURE, WHICH SUPPORTS THE CURRENT POSITION WITH GOOD
CONFIDENCE. THE CURRENT INTENSITY IS ASSESSED AT 65 KNOTS BASED ON A
PGTW DVORAK INTENSITY ESTIMATE OF T4.0 (65 KNOTS), CONSISTENT WITH
THE VISIBLE EYE STRUCTURE. UPPER-LEVEL ANALYSIS INDICATES LOW TO
MODERATE (10-20 KNOTS) VERTICAL WIND SHEAR OFFSET BY ROBUST POLEWARD
OUTFLOW INTO A DEEP UPPER-LEVEL TROUGH TO THE NORTH. SST VALUES OF
27-28C REMAIN CONDUCIVE FOR FURTHER DEVELOPMENT. THE SYSTEM IS
TRACKING ALONG THE SOUTHWESTERN PERIPHERY OF A SUBTROPICAL RIDGE
(STR) POSITIONED TO THE 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 TURN NORTHWARD TO NORTH-NORTHEASTWARD
WITHIN THE NEXT 12-24 HOURS AS IT BEGINS TO RECURVE ALONG THE
WESTERN PERIPHERY OF THE STR. BY TAU 36, THE SYSTEM WILL BEGIN TO
INTERACT WITH A DEEP MIDLATITUDE SHORTWAVE TROUGH POSITIONED OVER
THE EAST CHINA SEA AND RYUKYU ISLANDS, AND BEGIN EXTRA-TROPICAL
TRANSITION (ETT). THE SYSTEM IS EXPECTED TO INTENSIFY SLIGHTLY TO A
PEAK INTENSITY OF 75 KNOTS BY TAU 12, HOWEVER, VWS IS EXPECTED TO
INCREASE SIGNIFICANTLY BY TAU 24 (35 KNOTS), WHICH WILL SERVE TO
WEAKEN THE SYSTEM. AFTER TAU 24, TY 21W WILL ENCOUNTER INCREASING
VWS (45-75 KNOTS) AS IT BECOMES EMBEDDED WITHIN THE MIDLATITUDE
WESTERLIES AND SHOULD COMPLETE ETT BY TAU 72. 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 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 60.
HOWEVER, EXTREMELY STRONG VWS WILL SHRED THE DEEP CONVECTION OVER
THE SYSTEM.
   C. BEYOND TAU 72, TY 21W IS EXPECTED TO ACCELERATE NORTHEASTWARD
AS IT TRACKS UNDER A SOUTHWESTERLY JET. THIS EXTRA-TROPICAL SYSTEM
IS EXPECTED TO MAINTAIN GALE-FORCE WINDS 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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