Tropical Storm VONGFONG Advisory Mon Oct 13

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 19W (VONGFONG) WARNING
NR 39//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL STORM (TS) 19W (VONGFONG), LOCATED APPROXIMATELY 285 NM
SOUTH-SOUTHWEST OF SASEBO, JAPAN, HAS TRACKED NORTHWARD AT 12
KNOTS OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE
IMAGERY (MSI) DEPICTS A TIGHTLY-WRAPPED, PARTIALLY-EXPOSED LOW-LEVEL
CIRCULATION CENTER (LLCC) WITH DEEP CONVECTION SHEARED OVER THE
NORTHEASTERN QUADRANT OF THE LLCC. BASED ON MSI, THERE IS GOOD
CONFIDENCE IN THE INITIAL POSITION AND THE RECENT GENERAL MOTION
NORTHWARD TO NORTH-NORTHEASTWARD (PAST FEW HOURS). A 120439Z TRMM
37GHZ IMAGE REVEALS A WELL-DEFINED LLCC WITH TIGHTLY-CURVED SHALLOW
BANDING WRAPPING INTO A BROAD CENTER. A 120052Z ASCAT IMAGE DEPICTS
NUMEROUS 50 TO 55 KNOT WIND VECTORS, WHICH INFERS A 55- TO 60-KNOT
SYSTEM, WHICH ALONG WITH DVORAK CURRENT INTENSITY ESTIMATES OF 65
KNOTS SUPPORTS THE INITIAL INTENSITY ASSESSMENT OF 60 KNOTS. UPPER-
LEVEL ANALYSIS, ALONG WITH ANIMATED WATER VAPOR IMAGERY, REVEALS A
DEGRADING ENVIRONMENT AS STRONG (30 TO 40 KNOTS) SOUTHWESTERLY
VERTICAL WIND SHEAR IS OFFSET BY ENHANCED POLEWARD OUTFLOW INTO THE
MIDLATITUDE WESTERLIES. TS 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 FORECAST TO TURN SHARPLY EAST-NORTHEASTWARD AND TO
ACCELERATE WITHIN THE NEXT 12 HOURS. TS 19W SHOULD ALSO BEGIN EXTRA-
TROPICAL TRANSITION (ETT) AS IT BEGINS TO INTERACT WITH AN
APPROACHING MIDLATITUDE SHORTWAVE TROUGH, WHICH IS CURRENTLY
DEEPENING OVER THE WEST SEA AND THE KOREAN PENINSULA. THE DYNAMIC
MODELS HAVE STABILIZED AND ARE IN TIGHT AGREEMENT, THEREFORE, THERE
IS HIGH CONFIDENCE IN THE JTWC FORECAST TRACK, WHICH IS POSITIONED
CLOSE TO THE MULTI-MODEL CONSENSUS. THE DYNAMIC MODELS ALSO ARE
CONSISTENT IN THE TIMING OF ETT AND INDICATE THAT TS 19W WILL
COMPLETE ETT AS IT NEARS THE KANTO PLAIN. THE SYSTEM WILL CLEARLY
GAIN STRONG FRONTAL CHARACTERISTICS AS IT BECOMES EMBEDDED WITHIN
THE MIDLATITUDE WESTERLIES BY TAU 36. TS 19W IS EXPECTED TO REMAIN A
GALE-FORCE COLD-CORE LOW WITH A BROAD LOW-LEVEL WIND FIELD AS IT
TRACKS OVER THE KANTO PLAIN.//
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