Tropical Storm HALONG Advisory Fri Aug 01

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 11W (HALONG) WARNING NR
12//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL STORM (TS) 11W (HALONG), LOCATED APPROXIMATELY 230 NM
WEST-NORTHWEST OF NAVSTA GUAM, HAS TRACKED WEST-NORTHWESTWARD AT 08
KNOTS OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE
IMAGERY (MSI) REVEALS A TIGHTLY WRAPPED LOW LEVEL CIRCULATION CENTER
(LLCC) WITH BUILDING DEEP CONVECTION ACROSS THE SOUTHERN SEMI-CIRCLE
THAT IS STARTING TO OBSCURE THE LLCC. A 310454Z AMSU-B MICROWAVE
IMAGE SHOWS THE CONVECTION HAS BEEN ABLE TO BUILD AND BECOME MORE
ATTACHED TO THE LLCC WHICH SUGGEST THE STRONG VERTICAL WIND SHEAR
(VWS) HAS SLIGHTLY WEAKENED. THE INITIAL POSITION IS BASED UPON MSI
LOOP WITH GOOD CONFIDENCE DUE TO THE WELL DEFINED NATURE OF THE
LLCC. THE INITIAL INTENSITY HAS BEEN MAINTAINED AT 45 KNOTS DUE TO
THE TIGHTLY WRAPPED STRUCTURE AND DVORAK CURRENT INTENSITY ESTIMATES
OF THE SAME VALUE FROM PGTW AND RJTD. UPPER LEVEL ANALYSIS, ALONG
WITH WATER VAPOR IMAGERY, DEPICTS STRONG (25 TO 30 KNOTS) VWS
CONTINUES TO ACT UPON THE SYSTEM, WHICH IS OFFSETTING VIGOROUS
EQUATORWARD OUTFLOW. TS 11W IS TRACKING WESTWARD ALONG THE SOUTHERN
PERIPHERY OF THE SUBTROPICAL RIDGE (STR) TO THE NORTH.
3. FORECAST REASONING.
   A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS
PROGNOSTIC REASONING MESSAGE.
   B. TS 11W IS EXPECTED TO TRACK WEST-NORTHWESTWARD UNDER THE
STEERING INFLUENCE OF THE STR THROUGH TAU 48. RECENT GUIDANCE SHOWS
THE STR WILL BUILD WESTWARD AS THE MONSOON DEPRESSION (INVEST 96W)
TRACKS TOWARD SOUTH KOREA. AFTER TAU 48, THE MONSOON DEPRESSION WILL
BEGIN TO INTERACT WITH THE MID-LATITUDE FLOW, EVENTUALLY BEING
ABSORBED WITHIN THE WESTERLY JET AND TRACKING OVER THE SEA OF JAPAN.
THIS WILL CAUSE THE STR TO SHIFT, ALLOWING FOR A MORE NORTHWESTWARD
TRACK PAST TAU 72. THE PERSISTENT VWS WILL PREVENT A RAPID
INTENSIFICATION THROUGH TAU 48. CURRENT INDICATIONS ARE THAT AS THE
SYSTEM MOVES TO THE WEST, THE UPPER LEVEL ENVIRONMENT WILL SEE
MARGINAL IMPROVEMENTS, ALLOWING A DECREASE IN VWS AND A PERIOD OF
QUICKER INTENSIFICATION THROUGH TAU 72.
   C. TS HALONG IS EXPECTED TO TRACK SLOWLY NORTH-NORTHWESTWARD
ALONG THE WESTERN PERIPHERY OF THE STR IN THE EXTENDED TAUS AND
SLIGHTLY WEAKEN AS IT TRACKS INTO NORTHERLY UPPER-LEVEL FLOW AND
INCREASING VWS ASSOCIATED WITH A BROAD UPPER-LEVEL HIGH TO THE
NORTHWEST. NUMERIC MODEL GUIDANCE IS IN FAIRLY TIGHT AGREEMENT
THROUGH TAU 48 AND SLIGHTLY DIVERGES AFTER WHICH WITH SOME
DISAGREEMENT IN THE EXTENT OF THE RIDGE BUILDING FURTHER TO THE
WEST. DUE TO THIS UNCERTAINTY IN THE MOVEMENT OF THE RIDGE, THERE IS
OVERALL LOW CONFIDENCE IN THE JTWC FORECAST.//
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