Tropical Storm SONGDA Advisory Wed Oct 12

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 23W (SONGDA) WARNING NR 13//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TYPHOON (TY) 23W (SONGDA), LOCATED APPROXIMATELY 537 NM SOUTHEAST
OF YOKOSUKA, JAPAN, HAS TRACKED NORTHEASTWARD AT 10 KNOTS OVER THE
PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY SHOWS A
10-NM EYE THAT IS BECOMING CLOUD-FILLED AS THE SYSTEM BECOMES MORE
RAGGED AND ELONGATED DUE TO HIGH VERTICAL WIND SHEAR (VWS) ASSOCIATED
WITH THE MID-LATITUDE WESTERLIES. THE CURRENT POSITION IS BASED ON
THE EYE FEATURE WITH HIGH CONFIDENCE. THE INTENSITY OF 90 KNOTS IS
BASED ON AN OVERALL ASSESSMENT OF AGENCY AND OBJECTIVE DVORAK
ESTIMATES AND REFLECTS THE DEGRADATION. UPPER LEVEL ANALYSIS
INDICATES THE SYSTEM HAS DRIFTED DEEPER INTO THE PREVAILING
WESTERLIES WITH STRONG (25-30 KNOT) VWS. THE CYCLONE HAS BEGUN TO
ACCELERATE NORTHEASTWARD ON THE POLEWARD SIDE OF THE SUBTROPICAL
RIDGE.
3. FORECAST REASONING.
   A. NO SIGNIFICANT CHANGE TO THE FORECAST PHILOSOPHY FROM THE
PREVIOUS PROGNOSTIC REASONING MESSAGE.
   B. TY SONGDA WILL CONTINUE ACCELERATING NORTHEASTWARD AS IT EMBEDS
DEEPER WITHIN THE MID-LATITUDE WESTERLY FLOW. INCREASING VWS AND
COOLING SEA SURFACE TEMPERATURES WILL RAPIDLY ERODE THE SYSTEM. BY
TAU 24, TY 23W WILL BEGIN EXTRA-TROPICAL TRANSITION (ETT) AND BY THE
END OF THE FORECAST PERIOD, THE SYSTEM WILL COMPLETE ETT AND BE
REDUCED TO A 40-KNOT COLD-CORE LOW. THERE IS HIGH CONFIDENCE IN THE
FORECAST DUE TO VERY TIGHT AGREEMENT IN ALL MODEL TRACKERS.//
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