Tropical Storm VONGFONG Advisory Sat Oct 04

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 19W (VONGFONG) WARNING
NR 06//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL STORM (TS) 19W (VONGFONG), LOCATED APPROXIMATELY 637 NM
EAST-SOUTHEAST OF SAIPAN, HAS TRACKED WEST-NORTHWESTWARD AT 13 KNOTS
OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY
(MSI) SHOWS DEEPENED CENTRAL CONVECTION WITH FORMATIVE BANDING OVER
THE NORTHERN SEMI-CIRCLE WRAPPING INTO A CONSOLIDATING LOW-LEVEL
CIRCULATION CENTER. A 032328Z METOP-A MICROWAVE IMAGE REVEALS
TIGHTLY-CURVED BANDING AROUND A WELL-DEFINED MICROWAVE EYE. THE
CURRENT POSITION IS BASED ON THE MSI ANIMATION AND METOP-A MICROWAVE
IMAGE WITH HIGH CONFIDENCE. THE INITIAL INTENSITY HAS INCREASED TO
55 KNOTS BASED ON AN OVERALL ASSESSMENT OF DVORAK INTENSITY
ESTIMATES FROM PGTW AND KNES AND IMPROVED STRUCTURE OVER THE PAST
SIX HOURS. UPPER-LEVEL ANALYSIS INDICATES THE SYSTEM REMAINS IN A
FAVORABLE ENVIRONMENT WITH LOW VERTICAL WIND SHEAR AND EXCELLENT
OUTFLOW, ENHANCED BY THE TUTT POSITIONED TO THE NORTHEAST. TS 19W IS
TRACKING ALONG THE SOUTHERN PERIPHERY OF A SUBTROPICAL RIDGE (STR).
3. FORECAST REASONING.
   A. DUE TO IMPROVING STRUCTURE AND RAPID CONSOLIDATION, THE
FORECAST INTENSITY HAS BEEN INCREASED THROUGHOUT THE FORECAST
PERIOD. THE SYSTEM IS EXPECTED TO REACH TYPHOON STRENGTH BY TAU 12.
OTHERWISE, THERE IS NO SIGNIFICANT CHANGE TO THE FORECAST TRACK
PHILOSOPHY FROM THE PREVIOUS PROGNOSTIC REASONING MESSAGE.
   B. TS 19W WILL CONTINUE TRACKING WEST-NORTHWESTWARD UNDER THE
STEERING INFLUENCE OF THE STR THROUGH TAU 72. DYNAMIC MODEL GUIDANCE
HAS SLIGHTLY IMPROVED AND REMAINS IN GOOD AGREEMENT WITH A 70-NM
SPREAD IN SOLUTIONS AS THE SYSTEM TRACKS OVER THE MARIANAS.
ENVIRONMENTAL CONDITIONS WILL CONTINUE TO IMPROVE, ALLOWING TS 19W
TO REACH TYPHOON STRENGTH OVER THE NEXT 12 HOURS.
   C. TS 19W IS FORECAST TO TRACK NORTHWESTWARD UNDER STEERING
INFLUENCE OF THE STR THROUGH THE REMAINDER OF THE FORECAST PERIOD.
FAVORABLE CONDITIONS ARE EXPECTED TO PERSIST ALLOWING TS 19W TO
FURTHER INTENSIFY. AFTER TAU 96, A UPPER-LEVEL TROUGH PASSING OVER
SOUTHERN JAPAN CAUSES A BREAK IN THE STR ALLOWING TS 19W TO SHIFT
POLEWARD. DUE TO UNCERTAINTY IN THE SHORT-TERM INTENSITY AND THE
EXTENT OF THE UPPER-LEVEL TROUGH IN THE EXTENDED TAUS, THERE IS
OVERALL LOW CONFIDENCE IN THE JTWC FORECAST.//
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