Tropical Storm VONGFONG Advisory Thu Oct 09

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR SUPER TYPHOON 19W (VONGFONG) WARNING
NR 26//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   SUPER TYPHOON (STY) 19W (VONGFONG), LOCATED APPROXIMATELY 460 NM
SOUTH-SOUTHEAST OF KADENA AB, OKINAWA, JAPAN HAS TRACKED WEST-
NORTHWESTWARD AT 05 KNOTS OVER THE PAST SIX HOURS. ANIMATED
MULTISPECTRAL SATELLITE IMAGERY (MSI) SHOWS A ROUND 20-NM EYE WITH
SLIGHTLY WEAKENED CONVECTIVE BANDING WRAPPING INTO THE CENTER. THE
CURRENT POSITION IS BASED ON THE EYE FEATURE ON THE MIS WITH HIGH
CONFIDENCE. THE INITIAL INTENSITY OF 145 KNOTS IS BASED ON AN
OVERALL ASSESSMENT OF DVORAK CURRENT INTENSITY ESTIMATES RANGING
FROM 140 TO 155 KNOTS FROM ALL REPORTING AGENCIES AND WEAKENING
TREND. UPPER-LEVEL ANALYSIS CONTINUES TO INDICATE EXCELLENT RADIAL
OUTFLOW, AS EVIDENT ON THE WATER VAPOR IMAGERY, SUSTAINING THE
CONVECTION. STY 19W IS CURRENTLY TRACKING ALONG THE SOUTHWEST
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. STY 19W IS EXPECTED TO TRACK WEST-NORTHWESTWARD TO
NORTHWESTWARD OVER NEXT 18 HOURS AS IT ROUNDS THE SOUTHWEST
PERIPHERY OF THE STR. BY TAU 24, A MIDLATITUDE SHORTWAVE TROUGH IS
FORECAST TO DIG OVER WESTERN JAPAN MODIFYING THE STR, WHICH WILL
SHIFT STY 19W POLEWARD THROUGH TAU 48. AFTERWARDS, THE STR WILL
REBUILD IN RESPONSE TO A MIGRATORY SHORTWAVE RIDGE FROM THE
NORTHWEST, SLIGHTLY SHIFTING STY 19W TO A MORE NORTH-NORTHWESTWARD
TRACK. AVAILABLE MODEL GUIDANCE HAS IMPROVED OVER THE PAST SIX
HOURS, BUT STILL INDICATES A 150-NM SPREAD AT TAU 72. JTWC TRACK
FORECAST CONTINUES TO FAVOR THE GENERALLY NORTHWARD TRACK THROUGH
TAU 72 UNDER THE COMPLEX STEERING ENVIRONMENT OF A FAST MOVING WAVE-
TRAIN UPPER-LEVEL PATTERN.
   C. IN THE EXTENDED TAUS, ANOTHER MIDLATITUDE TROUGH PASSING OVER
THE KOREA PENINSULA WILL WEAKEN THE STR AND ALLOW THE SYSTEM RE-
CURVE NORTHEASTWARD. CONCURRENTLY, THE SYSTEM WILL BEGIN EXTRA-
TROPICAL TRANSITION AS IT INTERACTS WITH THE MIDLATITUDE WESTERLIES.
INTERACTION WITH THE WESTERLIES WILL RAPIDLY DECAY STY 19W FOR THE
REMAINDER OF THE FORECAST PERIOD. DUE TO UNCERTAINTY IN THE EXTENT
OF THE MIDLATITUDE TROUGH INTERACTION , THERE IS LOW CONFIDENCE IN
THE JTWC TRACK FORECAST.//
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