Tropical Storm SANBA Advisory Pzt, 17.09.

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 17W (SANBA) WARNING NR 25//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TYPHOON 17W (SANBA), LOCATED APPROXIMATELY 205 NM SOUTH-SOUTHWEST
OF PUSAN, SOUTH KOREA, HAS TRACKED NORTHWARD AT 17 KNOTS OVER THE
PAST SIX HOURS. THE CURRENT POSITION IS BASED ON RECENT SATELLITE
FIXES FROM PGTW AND RJTD AND A 19800Z RADAR FIX FROM JAPAN. THE
CURRENT INTENSITY OF 85 KNOTS IS CONSISTENT WITH DVORAK ESTIMATES
FROM KNES, PGTW, AND RJTD. RECENT ANIMATED INFRARED SATELLITE
IMAGERY SHOWS THE CONVECTIVE STRUCTURE OF 17W BEGINNING TO BREAK
DOWN AS THE SYSTEM ENTERS AN AREA OF INCREASING SOUTHWESTERLY
VERTICAL WIND SHEAR AHEAD OF A MIDLATITUDE TROUGH TO THE NORTHWEST.
DESPITE INCREASING SHEAR, THE CYCLONE HAS MANAGED TO MAINTAIN A
ROUGHLY 8 NM RAGGED EYE FEATURE FOR THE PAST SIX HOURS. TY 17W
CONTINUES TO TRACK POLEWARD AHEAD OF THE AFOREMENTIONED MIDLATITUDE
TROUGH UNDER THE STEERING INFLUENCE OF A DEEP-LAYERED SUBTROPICAL
RIDGE POSITIONED TO THE EAST OF JAPAN.
3. FORECAST REASONING.
   A. NO SIGNIFICANT CHANGE TO THE FORECAST PHILOSOPHY SINCE THE
PREVIOUS PROGNOSTIC REASONING MESSAGE.
   B. TY 17W WILL ACCELERATE NORTH-NORTHEASTWARD ACROSS THE KOREAN
PENINSULA OVER THE NEXT 24 HOURS IN THE GRADIENT BETWEEN THE CURRENT
STEERING RIDGE AND THE APPROACHING MIDLATITUDE TROUGH THE NORTHWEST.
THE SYSTEM WILL BEGIN EXTRATROPICAL TRANSITION AS IT ENTERS A
BAROCLINIC ZONE WITHIN THE NEXT 12 HOURS AND WILL RAPIDLY TRANSITION
INTO A FULLY EXTRATROPICAL LOW BY TAU 24. ALTHOUGH INTERACTION WITH
THE TAEBAEK MOUNTAIN RANGE AND INCREASING VERTICAL WIND SHEAR ARE
EXPECTED TO INDUCE STEADY WEAKENING, THE SYSTEM SHOULD MAINTAIN GALE-
FORCE INTENSITY UNDER THE INFLUENCE STRONG POLEWARD DIVERGENCE ALOFT
DURING EXTRATROPICAL TRANSITION. THE AVAILABLE NUMERICAL GUIDANCE
REMAINS IN VERY TIGHT AGREEMENT. THE CURRENT FORECAST LIES SLIGHTLY
TO THE RIGHT AND FASTER THAN THE MODEL CONSENSUS IN ANTICIPATION OF
A SLIGHTLY STRONGER NORTH-NORTHEASTWARD STEERING FLOW THAN DEPICTED
IN MANY OF THE CONSENSUS MEMBER MODEL FIELDS. THERE IS HIGH
CONFIDENCE IN THE TRACK FORECAST.//
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