Tropical Storm HALONG Advisory Wed Jul 30

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 11W (HALONG) WARNING NR
04//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL STORM (TS) 11W (HALONG), LOCATED APPROXIMATELY 191 NM
EAST-SOUTHEAST OF ANDERSEN AFB, HAS TRACKED NORTHWESTWARD AT 05 KNOTS
OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE IMAGERY
(MSI) DEPICTS A CONSOLIDATING LOW-LEVEL CIRCULATION CENTER (LLCC)
WITH CURVED CONVECTIVE BANDING WRAPPING INTO A WELL-DEFINED CENTER.
FOR A BRIEF PERIOD OF TIME, THE MSI DEPICTED A WEAK EYE, HOWEVER,
RECENT IMAGERY INDICATES THAT THIS FEATURE WAS LIKELY SPURIOUS. A
290512Z SSMI 37 GHZ IMAGE, REVEALS IMPROVED CONVECTIVE BANDING OVER
THE SOUTHERN SEMI-CIRCLE AND SHOWS A WELL-DEFINED CENTER, HOWEVER,
THE BANDING IS WEAKER OVER THE NORTHERN SEMI-CIRCLE. THIS IS
EVIDENCED BY THE 282314Z ASCAT IMAGE WHICH SHOWED GALE-FORCE WINDS
(AS HIGH AS 40 TO 45 KNOTS) OVER THE SOUTHERN SEMI-CIRCLE AND WEAKER
WINDS OVER THE NORTHERN SEMI-CIRCLE. THIS ASCAT IMAGE WAS USED TO
DERIVE THE 34-KNOT WIND RADII AT 29/06Z. THERE IS GOOD CONFIDENCE IN
THE CURRENT POSITION BASED ON THE AFOREMENTIONED IMAGERY AS WELL AS
A RADAR FIX AT 29/0630Z. THE INITIAL INTENSITY IS ASSESSED AT 50
KNOTS, HEDGED SLIGHTLY HIGHER THAN THE DVORAK INTENSITY ESTIMATE OF
45 KNOTS, BASED ON THE IMPROVED CONVECTIVE STRUCTURE. UPPER-LEVEL
ANALYSIS INDICATES ENHANCED OUTFLOW SUPPORTED BY A TUTT CELL TO THE
NORTHEAST AND A WEAK TUTT CELL TO THE NORTHWEST. TS 11W IS TRACKING
SLOWLY NORTHWESTWARD ALONG THE SOUTHWESTERN PERIPHERY OF THE
SUBTROPICAL RIDGE (STR).
3. FORECAST REASONING.
   A. NO SIGNIFICANT CHANGES TO THE FORECAST PHILOSOPHY SINCE THE
PREVIOUS PROGNOSTIC REASONING. PEAK INTENSITY HAS BEEN INCREASED
SLIGHTLY AT CPA TO GUAM (TO 65 KNOTS) BUT CPA HAS REMAINED VERY
CONSISTENT.
   B. AS THE MONSOON DEPRESSION (INVEST 96W) TRACKS NORTH-
NORTHWESTWARD TOWARD OKINAWA, THE STR IS FORECAST TO BUILD NORTH OF
THE SYSTEM PROVIDING A WESTWARD TO WEST-NORTHWESTWARD STEERING
INFLUENCE THROUGH TAU 36. AFTER TAU 36, THE STR SHOULD MAINTAIN A
NORTHWEST-SOUTHEAST ORIENTATION, WHICH WILL STEER TS 11W
NORTHWESTWARD THROUGH TAU 72. DYNAMIC GUIDANCE IS IN TIGHT AGREEMENT
WITH A 100 NM SPREAD IN SOLUTIONS NEAR TAU 72. TS 11W IS FORECAST TO
INTENSIFY THROUGH TAU 72 TO A PEAK INTENSITY OF 85 KNOTS.
ENVIRONMENTAL CONDITIONS ARE CURRENTLY FAVORABLE BUT THE OVERALL
SYNOPTIC PATTERN IS COMPLEX WITH TUTT CELLS ENHANCING THE OUTFLOW,
THEREFORE, THERE IS MODERATE UNCERTAINTY IN THE INTENSITY FORECAST.
   C. IN THE EXTENDED TAUS, UNCERTAINTY IN THE TRACK INCREASES
SLIGHTLY AS THE DYNAMIC GUIDANCE DIVERGES. NAVGEM PRESENTS THE MOST
UNREALISTIC SCENARIO WITH A NORTHWARD TRACK INTO THE STR, THEREFORE,
THE JTWC FORECAST FAVORS A NORTHWESTWARD TRACK CLOSER TO ECMWF AND
GFS. TS HALONG SHOULD WEAKEN AFTER TAU 96 AS IT ENCOUNTERS
INCREASING VERTICAL WIND SHEAR ASSOCIATED WITH UPPER-LEVEL NORTHERLY
FLOW ALONG THE EASTERN FLANK OF THE UPPER-LEVEL HIGH. DUE TO THE
INCREASED UNCERTAINTY IN THE TRACK AND INTENSITY FORECAST AT THE
EXTENDED TAUS, THERE IS OVERALL LOW CONFIDENCE IN THE JTWC
FORECAST.//
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