Tropical Storm VONGFONG Advisory Sun Oct 12

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 19W (VONGFONG) WARNING NR 35//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TYPHOON (TY) 19W (VONGFONG), LOCATED APPROXIMATELY 89 NM SOUTH-
SOUTHEAST OF KADENA AB, HAS TRACKED NORTH-NORTHWESTWARD AT 08 KNOTS
OVER THE PAST SIX HOURS. ANIMATED ENHANCED INFRARED SATELLITE
IMAGERY DEPICTS A GENERAL WEAKENING TREND WITH WARMING CLOUD TOP
TEMPERATURES AND, AS DEPICTED IN A 110558Z SSMI IMAGE, DECAYING DEEP
CONVECTION OVER THE SOUTHERN SEMI-CIRCLE DUE TO INCREASING (20 TO 30
KNOTS) SOUTHWESTERLY VERTICAL WIND SHEAR (VWS). THE 50-KNOT WIND
RADII HAVE BEEN ADJUSTED BASED ON SURFACE OBSERVATIONS FROM KADENA
AB. RECENT ASCAT IMAGERY INDICATES EXTENSIVE GALE-FORCE WINDS OUT AS
FAR AS 250 TO 300 NM, HOWEVER, THESE PERIPHERAL WINDS APPEAR TO BE
ENHANCED BY GRADIENT COMPRESSION. BASED ON RADAR FIXES FROM THE JMA
AND A DEFINED CENTER, THERE IS GOOD CONFIDENCE IN THE INITIAL
POSITION. THE INITIAL INTENSITY IS ASSESSED AT 85 KNOTS BASED ON
DVORAK CURRENT INTENSITY ESTIMATES RANGING FROM 77 TO 90 KNOTS.
KADENA SURFACE OBSERVATIONS INDICATE SUSTAINED NORTHERLY WINDS AS
HIGH AS 50 TO 55 KNOTS WITH GUSTS AS UP TO 76 KNOTS THUS FAR.
ANIMATED WATER VAPOR IMAGERY CONTINUES TO INDICATE STRONG POLEWARD
OUTFLOW INTO THE MIDLATITUDE WESTERLIES. TY 19W IS TRACKING
NORTHWARD ALONG THE NORTHWESTERN PERIPHERY OF THE SUBTROPICAL RIDGE
(STR).
3. FORECAST REASONING.
   A. THERE IS NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE
PREVIOUS PROGNOSTIC REASONING MESSAGE.
   B. THE 11/00Z 500 MB ANALYIS DEPICTS A TRANSITORY MIDLATITUDE
SHORTWAVE RIDGE POSITIONED NORTH OF THE SYSTEM, OVER THE KOREAN
PENINSULA, WITH A DEEP MIDLATITUDE SHORTWAVE TROUGH DIGGING INTO
CENTRAL CHINA. AS THE DYNAMIC MODELS INDICATE, THIS TRANSITORY RIDGE
IS FORECAST TO SHIFT EASTWARD OVER THE NEXT 24 HOURS WITH THE
SHORTWAVE TROUGH PROPAGATING INTO EASTERN ASIA. CONSEQUENTLY, EXPECT
TY 19W TO TRACK SLOWLY NORTH-NORTHWESTWARD TO NORTHWARD THROUGH TAU
24 THEN SHARPLY RE-CURVE EAST-NORTHEASTWARD AS THE SYSTEM BEGINS TO
INTERACT WITH THE MIDLATITUDE WESTERLIES. NEAR TAU 36, TY 19W SHOULD
BEGIN EXTRA-TROPICAL TRANSITION (ETT) AS IT INTERACTS WITH THE
BAROCLINIC ZONE. TY 19W SHOULD WEAKEN RAPIDLY AFTER TAU 36, AS VWS
AND LAND INTERACTION INCREASE. TY 19W SHOULD COMPLETE ETT NEAR THE
KANTO PLAIN AS THE SYSTEM GAINS FRONTAL CHARACTERISTICS AND BECOMES
EMBEDDED WITHIN STRONG MIDLATITUDE WESTERLIES. FURTHER WEAKENING
WILL OCCUR AS THE SYSTEM TRACKS ACROSS THE MOUNTAINOUS REGION OF
JAPAN WITH A 35-KNOT COLD CORE LOW EMERGING OVER WATER PRIOR TO TAU
72. DYNAMIC MODEL GUIDANCE IS IN TIGHT AGREEMENT, THEREFORE, THERE
IS HIGH CONFIDENCE IN THE JTWC FORECAST TRACK.//
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