Tropical Storm NEOGURI Advisory dom, 20-10

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 21W (NEOGURI) WARNING
NR 015//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TYPHOON 21W (NEOGURI), LOCATED APPROXIMATELY 186 NM SOUTH OF
KADENA AB, OKINAWA, JAPAN HAS TRACKED NORTH-NORTHEASTWARD AT 10 KNOTS
OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY
DEPICTS A COMPACT SYSTEM THAT HAS DETERIORATED SLIGHTLY OVER THE PAST
SIX HOURS AS THE CONVECTION IS OFFSET TO THE NORTH OF THE LOW-LEVEL
CIRCULATION CENTER (LLCC) CAUSED BY THE MODERATE TO STRONG (25-30
KTS) VERTICAL WIND SHEAR (VWS). THERE IS NO VISIBLE EYE, HOWEVER
CONFIDENCE IN THE INITIAL POSITION REMAINS GOOD BASED ON THE
EXTRAPOLATION FROM A WELL-DEFINED LOW BRIGHTNESS CIRCULATION FEATURE
IN THE 202233Z SSMIS 91GHZ IMAGE THAT LINED UP WELL WITH THE 20/00Z
AGENCY FIX CLUSTER. THE CURRENT INTENSITY IS ASSESSED AT 90 KTS BASED
ON A DECREASING TREND IN THE DVORAK INTENSITY ESTIMATES BY RJTD AND
PGTW AND CONSISTENT WITH A DETERIORATION IN THE STORM STRUCTURE.
HOWEVER, THE SIGNIFICANT VWS IS STILL BEING OFFSET BY ROBUST POLEWARD
OUTFLOW INTO A DEEP UPPER-LEVEL TROUGH TO THE NORTH THAT IS PROVIDING
VENTILATION TO THE CENTRAL CONVECTION. SST VALUES OF 27-28C REMAIN
CONDUCIVE. THE SYSTEM HAS CRESTED THE SUBTROPICAL RIDGE (STR) AXIS
AND IS TRACKING ALONG THE WESTERN/POLEWARD PERIPHERY OF THE STR
POSITIONED TO THE EAST.
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 24, TRANSITIONING TO A NORTHEASTWARD 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 HAS WEAKENED SLIGHTLY
OVER THE PAST SIX HOURS AND IS EXPECTED TO CONTINUE WEAKENING
STEADILY THROUGH TAU 72. AFTER TAU 24, VWS IS EXPECTED TO INCREASE
SIGNIFICANTLY AND MAINTAIN BETWEEN 45-60 KNOTS THROUGH TAU 72, WHICH
CONTRIBUTES TO THE SIGNIFICANT WEAKENING OF TY 21W. AFTER TAU 36, TY
21W BECOMES EMBEDDED WITHIN THE MIDLATITUDE WESTERLIES AND SHOULD
COMPLETE ETT BY TAU 48. BY TAU 72, TY 21W WILL BE REDUCED TO 35KTS.
THE MODELS ARE IN TIGHT AGREEMENT THROUGH TAU 36, LENDING FAIR
CONFIDENCE TO THIS PORTION OF THE JTWC TRACK FORECAST. HOWEVER, AFTER
TAU 36 THE GUIDANCE BEGINS TO EXCESSIVELY DIVERGE, WITH GFS NOTABLY
REVERSING THE TRACK SOUTHWESTWARD AND A NUMBER OF THE MODELS STOP
TRACKING THE SYSTEM AFTER TAU 60, LIKELY BECAUSE THE VORTICES BECOME
LOST IN THE BAROCLINIC ZONE AS TY 21W BECOMES EXTRA-TROPICAL AT THIS
TIME. DUE TO LARGE INCONSISTENCIES IN THE MODEL GUIDANCE BEYOND TAU
36 THE OFFICIAL TRACK FORECAST IS PRIMARILY EXTRAPOLATED OFF OF THE
192100Z JTWC FORECAST. THEREFORE, THERE IS LOW CONFIDENCE IN THIS
PORTION OF THE TRACK FORECAST.//
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