Tropical Storm SANBA Advisory Sun Sep 16

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 17W (SANBA) WARNING NR 24//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TYPHOON (TY) 17W (SANBA), LOCATED APPROXIMATELY 270 NM
SOUTH-SOUTHWEST OF PUSAN, SOUTH KOREA, HAS TRACKED JUST WEST OF
NORTHWARD AT 19 KNOTS OVER THE PAST SIX HOURS. ANIMATED INFRARED
SATELLITE IMAGERY SHOWS THE SYSTEM HAS WEAKENED AS TIGHT BANDING INTO
A 20-NM RAGGED EYE BEGAN TO UNRAVEL. THE INITIAL POSITION IS BASED
ON A MICROWAVE EYE FEATURE ON 161135Z SSMI-S IMAGE WITH HIGH
CONFIDENCE. THE INITIAL INTENSITY IS BASED ON DVORAK ESTIMATES FROM
PGTW, RJTD, AND KNES. UPPER LEVEL ANALYSIS SHOWS THE EQUATORWARD
OUTFLOW HAS SIGNIFICANTLY DECREASED AS THE BASE OF THE MID-LATITUDE
TROUGH DUG INTO THE SOUTHWEST QUADRANT OF THE CYCLONE. STRONG
POLEWARD OUTFLOW CONTINUES TO SUSTAIN 17W EVEN AS VERTICAL WIND
SHEAR (VWS), NOW AT 30-40 KNOTS, BECOMES EVEN STRONGER AS THE SYSTEM
EMBEDS DEEPER INTO THE SUBTROPICAL JET STREAM. THE CYCLONE CONTINUES
TO BE STEERED BY A DEEP-LAYERED SUBTROPICAL RIDGE (STR) TO THE EAST
OF JAPAN.
3. FORECAST REASONING.
   A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS
PROGNOSTIC REASONING MESSAGE.
   B. TY 17W IS FORECAST TO CONTINUE ACCELERATING AND TRACK ON A MORE
NORTH-NORTHEASTWARD TRAJECTORY AS THE MID-LATITUDE TROUGH WEAKENS THE
STEERING RIDGE. INCREASING VWS, DECREASING SEA SURFACE TEMPERATURES,
FOLLOWED BY LAND INTERACTION INTO THE RUGGED TERRAIN OF THE KOREAN
PENINSULA WILL RESULT IN A DRASTIC WEAKENING OF THE SYSTEM. ITS
REMNANTS WILL BEGIN EXTRATROPICAL TRANSITION BY TAU 12, BECOMING A
WEAK COLD CORE LOW BY TAU 24 AFTER EMERGING BACK IN THE COLD WATERS
OF THE SEA OF JAPAN. THE ALTERNATE SCENARIO IS THAT TYPHOON SANBA
WILL DISSIPATE IN THE TAEBAEK MOUNTAIN RANGE. THE AVAILABLE NUMERICAL
GUIDANCE IS IN VERY TIGHT AGREEMENT WITH SOME SPREAD AFTER TAU 24.
WBAR REMAINS THE SOLE LEFT OUTLIER. THERE IS HIGH CONFIDENCE IN THE
TRACK FORECAST, WHICH IS ADJUSTED SLIGHTLY RIGHT AND AHEAD OF
CONSENSUS TO OFFSET WBAR.    //
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