Tropical Storm VONGFONG Advisory Mon Oct 06

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 19W (VONGFONG) WARNING NR 14//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TYPHOON (TY) 19W (VONGFONG), LOCATED APPROXIMATELY 599 NM SOUTH
OF IWO TO, HAS TRACKED WEST-NORTHWESTWARD AT 18 KNOTS OVER THE PAST
SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY DEPICTS BROKEN
CONVECTIVE BANDING WRAPPING INTO A RE-CONSOLIDATING LOW-LEVEL
CIRCULATION CENTER (LLCC). THE SYSTEM HAS STRUGGLED IN DEVELOPMENT
DUE TO DEGRADED UPPER-LEVEL CONDITIONS OVER THE PAST 12 HOURS. A
052338Z METOP-B MICROWAVE IMAGE ALSO REVEALS THE BULK OF THE
CONVECTIVE BANDING OVER THE SOUTHERN PERIPHERY WRAPPING TOWARDS THE
LLCC. THE CURRENT POSITION IS BASED ON THE MSI AND 052308Z ASCAT
IMAGE WITH HIGH CONFIDENCE. THE INITIAL INTENSITY HAS DECREASED TO
80 BASED ON AN OVERALL ASSESSMENT OF DVORAK INTENSITY ESTIMATES FROM
ALL REPORTING AGENCIES AND CURRENT STRUCTURE. UPPER-LEVEL ANALYSIS
INDICATES THE SYSTEM REMAINS IN AN AREA OF MODERATE TO STRONG (20 TO
25 KNOT) VERTICAL WIND SHEAR (VWS) 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. DUE TO DEGRADED UPPER-LEVEL CONDITIONS AND SYSTEM STRUCTURE,
THE FORECAST INTENSITY HAS CHANGED SLIGHTLY THROUGHOUT THE FORECAST
PERIOD. OTHERWISE, THERE IS NO SIGNIFICANT CHANGE TO THE TRACK
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 72. UPPER-LEVEL CONDITIONS
ARE EXPECTED TO IMPROVE SLOWLY LEADING TO A GRADUAL INTENSIFICATION
AND REACHING 125 KNOTS BY TAU 72. DYNAMIC MODEL GUIDANCE REMAINS IN
TIGHT AGREEMENT LENDING HIGH CONFIDENCE TO THE FIRST 72 HOURS OF THE
FORECAST.
   C. TY VONGFONG IS EXPECTED TO TRACK ON A MORE POLEWARD DIRECTION
AS THE STR WEAKENS IN RESPONSE TO A MID-LATITUDE TROUGH APPROACHING
FROM THE NORTHWEST. DUE TO UNCERTAINTY IN THE STEERING ENVIRONMENT
BEYOND TAU 72, THE JTWC FORECAST CONFIDENCE LEVEL FOR THIS PORTION
OF THE FORECAST REMAINS LOW.//
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