Tropical Storm VONGFONG Advisory Sat Oct 11

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 19W (VONGFONG) WARNING NR 34//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TYPHOON (TY) 19W (VONGFONG), LOCATED APPROXIMATELY 137 NM SOUTH-
SOUTHEAST OF KADENA AB, OKINAWA, HAS TRACKED NORTH-NORTHWESTWARD AT
06 KNOTS OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE
IMAGERY (MSI) SHOWS THE EYE FEATURE OF THE SYSTEM HAS BECOME CLOUD
FILLED WHILE THE OVERALL STRUCTURE OF THE SYSTEM HAS STARTED TO
ELONGATE. A 102119Z SSMIS MICROWAVE PASS REVEALS THE SYSTEM HAS
REMAINED TIGHTLY WRAPPED ALTHOUGH THE BULK OF THE DEEP CONVECTION
HAS BECOME CONTAINED TO THE NORTHERN SEMI-CIRCLE. THE INITIAL
POSITION IS BASED ON THE WEAK EYE FEATURE IN THE MSI ANIMATION ALONG
WITH RADAR POSITION FIXES FROM RJTD WITH GOOD CONFIDENCE. THE
INITIAL INTENSITY OF 100 KNOTS IS BASED ON AN ASSESSMENT OF DVORAK
ESTIMATES FROM MULTIPLE REPORTING AGENCIES AND DUE TO THE WEAKENING
STRUCTURE. UPPER-LEVEL ANALYSIS INDICATES THE SYSTEM IS IN AN AREA
OF INCREASING (15-25 KNOT) VERTICAL WIND SHEAR (VWS) AND STRONG
OUTFLOW WHICH IS BEING ENHANCED ALONG THE POLEWARD SIDE DUE TO THE
MID-LATITUDE WESTERLIES. TY 19W IS TRACKING TO THE NORTH-NORTHWEST
ALONG A SUBTROPICAL RIDGE (STR) TO THE EAST AND A MIGRATORY RIDGE TO
THE NORTH.
3. FORECAST REASONING.
   A. THERE IS NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE
PREVIOUS PROGNOSTIC REASONING MESSAGE.
   B. TY 19W IS EXPECTED TO TRACK ON A NORTH-NORTHWESTWARD
TRAJECTORY OVER THE NEXT 36 HOURS IN RESPONSE TO THE AFOREMENTIONED
MIGRATORY RIDGE AS IT PASSES TO THE NORTH AND AS THE STR REMAINS TO
THE EAST OF THE SYSTEM. AFTER TAU 36, A MID-LATITUDE TROUGH
APPROACHING FROM THE NORTHWEST WILL WEAKEN THE RIDGE TO THE NORTH
AND PRESS UPON THE STR CAUSING THE CYCLONE TO RECURVE NORTHEASTWARD.
CONCURRENTLY, THE SYSTEM WILL BEGIN EXTRA-TROPICAL TRANSITION (ETT)
NEAR TAU 48 AS IT ACCELERATES NORTHEASTWARD THROUGH SOUTHERN JAPAN
AND BEGINS TO GAIN FRONTAL CHARACTERISTICS. AS THE SYSTEM GAINS
LATITUDE, INCREASING VWS ASSOCIATED WITH THE MID-LATITUDE WESTERLIES
WILL CONTINUE TO WEAKEN THE SYSTEM.
   C. AFTER TAU 72, CONTINUED INTERACTION WITH THE MID-LATITUDE
WESTERLIES AND JAPANS RUGGED TERRAIN WILL RAPIDLY WEAKEN THE SYSTEM
AS THE ETT PROCESS CONTINUES. BY TAU 96, THE SYSTEM IS EXPECTED TO
BECOME A GALE-FORCE, COLD-CORE LOW EAST OF HOKKAIDO. AVAILABLE MODEL
GUIDANCE IS OVERALL IN GOOD AGREEMENT, LENDING HIGH CONFIDENCE TO
JTWC TRACK FORECAST THAT IS POSITIONED CLOSE TO THE MULTI-MODEL
CONSENSUS.//
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