Tropical Storm TALIM Advisory Sun Sep 17

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 20W (TALIM) WARNING NR
31//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL STORM 20W (TALIM), LOCATED APPROXIMATELY 295 NM SOUTH-
SOUTHWEST OF SASEBO, JAPAN, HAS TRACKED EAST-NORTHEASTWARD AT 08
KNOTS OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE
IMAGERY DEPICTS A PARTIALLY EXPOSED LOW LEVEL CIRCULATION CENTER
(LLCC) WITH RELATIVELY WEAK AND SHALLOW CONVECTION ISOLATED TO THE
WESTERN PORTION OF THE SYSTEM. THERE IS HIGH CONFIDENCE IN THE
INITIAL POSITION BASED ON THE EXPOSED LLCC AND A 160546Z 37GHZ SSMI
IMAGE. THE INITIAL INTENSITY IS ASSESSED AT 55 KNOTS WHICH IS BASED
ON MULTI-AGENCY DVORAK ESTIMATES RANGING FROM T2.5 TO T4.5 (35 TO 77
KNOTS), A 160509Z SATCON ESTIMATE OF 52 KNOTS, AND A 160153Z METOP-B
ASCAT IMAGE SHOWING SEVERAL 50 KNOT WIND BARBS APPROXIMATELY 55 NM
WEST OF A WELL DEFINED LLCC. THE EXTENT OF GALE FORCE WINDS EXTENDS
WELL BEYOND PREVIOUS ESTIMATES, EVIDENT IN THE AFOREMENTIONED ASCAT
IMAGE, WITH THE WIND RADII NOW REFLECTING THESE DATA. UPPER-LEVEL
ANALYSIS SHOWS MODERATE VERTICAL WIND SHEAR ASSOCIATED WITH A WELL
ESTABLISHED UPPER-LEVEL RIDGE TO THE SOUTHEAST HINDERING EQUATORWARD
OUTFLOW. POLEWARD OUTFLOW REMAINS ROBUST FEEDING INTO THE MID-
LATITUDE JET WITH A DEVELOPING TROUGH JUST UPSTREAM. DUE TO THE SLOW
TRACK MOTION OF TY 20W OVER THE LAST SEVERAL DAYS, OCEAN UPWELLING
HAS BROUGHT COOLER WATERS TO THE SURFACE HELPING TO WEAKEN THE
SYSTEM. HOWEVER, SSTS BENEATH TS 20W ARE BEGINNING TO WARM AS THE
SYSTEM IS ACCELERATING EAST-NORTHEAST ALONG THE PERIPHERY OF A DEEP-
LAYERED SUBTROPICAL RIDGE (STR) TO THE SOUTHEAST.
3. FORECAST REASONING.
   A. THERE IS NO SIGNIFICANT CHANGE TO THE FORECAST PHILOSOPHY FROM
THE PREVIOUS PROGNOSTIC REASONING MESSAGE.
   B. TS 20W WILL CONTINUE TO ACCELERATE NORTHEASTWARD ALONG THE
NORTHWEST EXTENT OF THE STR FOR THE DURATION OF THE FORECAST. AS THE
SYSTEM TRACKS NORTHEASTWARD CONDITIONS WILL IMPROVE DUE TO WARMER
SSTS AND ENHANCED POLEWARD OUTFLOW AS THE TROUGH DEEPENS AND
APPROACHES TS 20W. SOUTHERLY WIND SHEAR IS EXPECTED TO REMAIN FAIRLY
STRONG OVER THE NEXT 24 HOURS WHICH WILL HELP MITIGATE A BRIEF
INTENSIFICATION PERIOD BEFORE TS 20W MAKES LANDFALL SOUTHEAST OF
SASEBO, JAPAN REACHING A PEAK INTENSITY OF 65 KNOTS. SHORTLY AFTER
TAU 24 TS 20W WILL BEGIN INTERACTING WITH THE APPROACHING TROUGH
WITH SUBSTANTIAL BAROCLINIC SUPPORT. TS 20W WILL TRANSITION INTO A
SIGNIFICANT EXTRATROPICAL LOW BY TAU 48 MAINTAINING GALE FORCE WINDS
WITH EXTENDED REACH, ESPECIALLY IN THE SOUTHEASTERN QUADRANT.
NUMERICAL MODEL GUIDANCE STILL SHOWS RELATIVELY TIGHT GROUPING WITH
A NOTABLE EASTWARD SHIFT IN THE ECMWF AND NAVGEM SOLUTIONS. DESPITE
THIS SHIFT, THERE REMAINS HIGH CONFIDENCE IN JTWC FORECAST TRACK
WHICH IS PLACED NEAR THE MULTI-MODEL CONSENSUS HEDGED SLIGHTLY
TOWARD ECMWF.//
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