Tropical Storm VONGFONG Advisory Tue Oct 07

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 19W (VONGFONG) WARNING NR 15//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TYPHOON (TY) 19W (VONGFONG), LOCATED APPROXIMATELY  534 NM SOUTH
OF IWO TO, JAPAN, HAS TRACKED WEST-NORTHWESTWARD AT 17 KNOTS OVER THE
PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY SHOWS THE
SYSTEM HAS BECOME MORE COMPACT AS IT BEGAN TO RE-CONSOLIDATE. THE
INITIAL POSITION IS BASED ON A MICROWAVE EYE FEATURE ON A 060532Z 37
GHZ SSMI PASS WITH HIGH CONFIDENCE. THE INITIAL INTENSITY OF 90 KNOTS
IS BASED ON AN OVERALL ASSESSMENT OF DVORAK INTENSITY ESTIMATES FROM
ALL REPORTING AGENCIES. UPPER-LEVEL ANALYSIS INDICATES THE SYSTEM
REMAINS IN AN AREA OF LIGHT TO MODERATE (10 TO 20 KNOT) VERTICAL WIND
SHEAR (VWS). HOWEVER, THE VWS IS OFFSET BY EXCELLENT EQUATORWARD
OUTFLOW. TY 19W IS CURRENTLY TRACKING ALONG THE SOUTHERN PERIPHERY
OF A DEEP-LAYERED SUBTROPICAL RIDGE (STR) TO THE NORTH.
3. FORECAST REASONING.
   A. THERE IS NO SIGNIFICANT CHANGE TO THE FORECAST PHILOSOPHY FROM
THE PREVIOUS PROGNOSTIC REASONING MESSAGE.
   B. TY 19W WILL CONTINUE TRACKING WEST-NORTHWESTWARD UNDER THE
STEERING INFLUENCE OF THE STR THROUGH TAU 48. AFTERWARDS, IT IS
EXPECTED TO TRACK MORE POLEWARD AS THE STR WEAKENS IN RESPONSE TO A
MID-LATITUDE TROUGH APPROACHING FROM THE NORTHWEST. UPPER-LEVEL
CONDITIONS ARE EXPECTED TO IMPROVE SLOWLY LEADING TO A GRADUAL
INTENSIFICATION AND REACHING 130 KNOTS BY TAU 72.
   C. TY VONGFONG IS EXPECTED TO TRACK POLEWARD ALONG THE WESTERN
EDGE OF THE AFOREMENTIONED STEERING STR. INCREASING VWS WILL
GRADUALLY WEAKEN THE CYCLONE AS IT GETS ABSORBED INTO THE
MID-LATITUDE WESTERLIES. DYNAMIC MODEL GUIDANCE IS IN TIGHT AGREEMENT
FOR THE FIRST HALF OF THE FORECAST THEN SIGNIFICANTLY SPREADS. IN
VIEW OF THIS, THERE IS HIGH CONFIDENCE IN THE FIRST HALF BUT LOW
CONFIDENCE IN THE SECOND HALF OF THE JTWC TRACK FORECAST.//
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