Tropical Storm VONGFONG Advisory Sun Oct 12

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 19W (VONGFONG) WARNING
NR 38//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL STORM (TS) 19W (VONGFONG), LOCATED APPROXIMATELY 79 NM
NORTH OF KADENA AB, OKINAWA, HAS TRACKED NORTH-NORTHWESTWARD AT 09
KNOTS OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE
IMAGERY (MSI) REVEALS A CONTINUED WEAKENING TREND AS COLD AIR
STRATOCUMULUS CLOUDS CAN BE OBSERVED STREAMING INTO THE WESTERN
PERIPHERY OF THE SYSTEM WHILE THE LOW LEVEL CIRCULATION CENTER
(LLCC) HAS BECOME OPEN AND ELONGATED. A RECENT 112336Z SSMIS
MICROWAVE IMAGE SHOWS THE CONVECTIVE ORGANIZATION HAS ALMOST
COMPLETELY DIMINISHED AS THE ONLY REMAINING DEEP CONVECTION HAS
BECOME CONTAINED TO THE NORTHERN FLANK. DUE TO THE BROAD
ORGANIZATION OF THE LLCC, THERE IS ONLY FAIR CONFIDENCE IN THE
INITIAL POSITION AND DIRECTION. THE INITIAL INTENSITY HAS BEEN
DECREASED TO 60 KNOTS BASED ON DECREASING DVORAK INTENSITY ESTIMATES
THAT RANGE FROM 55 TO 77 KNOTS AND AN 120052Z ASCAT PASS. UPPER
LEVEL ANALYSIS, ALONG WITH ANIMATED WATER VAPOR IMAGERY, REVEALS A
DEGRADING ENVIRONMENT AS STRONG (30 TO 40 KNOTS) SOUTHWESTERLY
VERTICAL WIND SHEAR IS OFFSETTING GOOD 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. TS 19W IS EXPECTED TO CONTINUE TO TRACK GENERALLY NORTH OVER
THE NEXT 12 HOURS ALONG THE NORTHWESTERN PERIPHERY OF THE STR. AFTER
WHICH, A DEEP MID-LATITUDE TROUGH, WHICH IS CURRENTLY DRAPED ACROSS
EASTERN CHINA, IS EXPECTED TO PROPAGATE EAST AND RE-ORIENT THE STR.
THIS WILL ACCELERATE THE SYSTEM TO NORTHEAST ACROSS SOUTHERN JAPAN.
AS THE SYSTEM ACCELERATES AND BECOMES FURTHER EMBEDDED INTO THE MID-
LATITUDE WESTERLIES, THE SYSTEM WILL BROADEN AND GAIN FRONTAL
CHARACTERISTICS AS IT BEGINS EXTRA-TROPICAL TRANSITION (ETT) NEAR
TAU 24. DUE TO THE CURRENTLY UNFAVORABLE UPPER-LEVEL ENVIRONMENT AND
EXPECTED ETT, THE SYSTEM IS FORECAST TO GENERALLY WEAKEN AS THE
STRONGEST WINDS ASSOCIATED WITH THE SYSTEM MIGRATE FROM THE CENTER
OF THE SYSTEM INTO THE DEVELOPING FRONTS. THE SYSTEM IS EXPECTED TO
BECOME A GALE FORCE, MID-LATITUDE LOW BY TAU 48 AS IT MOVES ACROSS
THE KANTO PLAIN. DYNAMIC MODEL GUIDANCE IS IN VERY GOOD AGREEMENT
WITH THE FORECAST SCENARIO AND TRACK, LENDING TO HIGH CONFIDENCE IN
THE FORECAST.//
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