Tropical Storm VONGFONG Advisory Sat Oct 11

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 19W (VONGFONG) WARNING NR 31//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TYPHOON (TY) 19W (VONGFONG), LOCATED APPROXIMATELY 265 NM
SOUTH-SOUTHEAST OF KADENA AB, OKINAWA, JAPAN, HAS TRACKED NORTHWARD
AT 08 KNOTS OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE
IMAGERY DEPICTS A 25 NM EYE THAT HAS BECOME MORE RAGGED AS THE
CONVECTIVE SIGNATURE BECAME MORE ELONGATED. THE INITIAL POSITION IS
BASED ON THE EYE FEATURE ON THE MSI LOOP AND EXTRAPOLATED FROM A
MICROWAVE EYE FEATURE ON A 100518Z AAMSU-B PASS WITH HIGH CONFIDENCE.
THE INITIAL INTENSITY OF 120 KNOTS IS BASED ON AN OVERALL ASSESSMENT
OF DVORAK CURRENT INTENSITY ESTIMATES FROM ALL REPORTING AGENCIES AND
REFLECTS THE WEAKENED STRUCTURE. UPPER-LEVEL ANALYSIS CONTINUES TO
INDICATE FAVORABLE VERTICAL WIND SHEAR (VWS) AND EXCELLENT OUTFLOW
THAT IS ENHANCING THE CONVECTION. TY 19W IS CURRENTLY TRACKING ALONG
THE WESTERN PERIPHERY OF AN EXTENSION OF THE SUBTROPICAL RIDGE (STR)
TO THE EAST.
3. FORECAST REASONING.
   A. THERE IS NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE
PREVIOUS PROGNOSTIC REASONING MESSAGE.
   B. TY 19W WILL CONTINUE TRACKING NORTHWARD OVER NEXT 24 HOURS AS
IT ROUNDS THE WESTERN EDGE OF THE PRIMARY STEERING STR. BETWEEN TAU
24 AND 36, A MIGRATORY SHORTWAVE RIDGE PASSING FROM THE NORTHWEST
WILL MOMENTARILY DEFLECT TY 19W NORTH-NORTHWESTWARD. THEN BY TAU 48,
A MID-LATITUDE TROUGH PASSING OVER THE KOREA PENINSULA WILL WEAKEN
THE PRIMARY STEERING STR AND CAUSE THE CYCLONE TO RECURVE
NORTH-NORTHEASTWARD. CONCURRENTLY, THE SYSTEM WILL BEGIN EXTRA-
TROPICAL TRANSITION (ETT) AS IT ACCELERATES NORTHEASTWARD THROUGH
SOUTHERN JAPAN. INCREASING VWS ASSOCIATED WITH THE MID-LATITUDE
WESTERLIES WILL WEAKEN THE SYSTEM TO 60 KNOTS BY TAU 72.
   C. IN THE EXTENDED TAUS, CONTINUED INTERACTION WITH THE
MID-LATITUDE WESTERLIES AND JAPAN'S RUGGED TERRAIN WILL RAPIDLY
WEAKEN TY VONGFONG. BY TAU 96, THE SYSTEM IS EXPECTED TO BECOME A
GALE-FORCE COLD-CORE LOW OVER NORTHERN JAPAN. AVAILABLE MODEL
GUIDANCE IS OVERALL IN GOOD AGREEMENT, LENDING HIGH CONFIDENCE TO
JTWC TRACK FORECAST THAT IS POSITIONED CLOSE TO AND SLIGHTLY FASTER
THAN THE MULTI-MODEL CONSENSUS.//
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