Tropical Storm FRANCISCO Advisory Wed Aug 07

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 09W (FRANCISCO) WARNING
NR 19//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL STORM (TS) 09W (FRANCISCO), LOCATED APPROXIMATELY 47 NM
SOUTHEAST OF BUSAN, SOUTH KOREA, HAS TRACKED NORTHWESTWARD AT 18
KNOTS OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE
IMAGERY SHOWS THE SYSTEM REMAINS INTACT AS IT EXITED KYUSHU INTO THE
TSUSHIMA STRAIT; HOWEVER, THE CENTRAL CONVECTION APPEARS TO BE
ERODING AS EVIDENCED BY WARMING TOPS AND ELONGATION ALONG THE
NORTHERN FLANKS. THE INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE
BASED ON A DEFINED LOW LEVEL CIRCULATION ON A COMPOSITE RADAR LOOP
FROM NORTHERN KYUSHU. THE INITIAL INTENSITY OF 50 KNOTS IS HELD
SLIGHTLY LOWER THAN AGENCY FIXES TO REFLECT THE RAPID WEAKENING
TREND. THE INITIAL POSITION AND INTENSITY ARE SUPPORTED BY NEARBY
SURFACE OBSERVATIONS INCLUDING THOSE FROM TSUSHIMA ISLAND, 10 NM TO
THE WEST. ENVIRONMENTAL ANALYSIS SHOWS TS 09W HAS DRIFTED INTO
INCREASING SOUTHEASTERLY VERTICAL WIND SHEAR (20 TO 25 KNOTS) CAUSING
A SLIGHT FORWARD TILT. THE VWS IS PARTLY OFFSET BY EXCELLENT POLEWARD
OUTFLOW AND MARGINAL SST (26 CELSIUS). THE CYCLONE IS TRACKING UNDER
THE INFLUENCE OF A SUBTROPICAL RIDGE (STR) LOCATED TO THE EAST-NORTHEAST.
3. FORECAST REASONING.
   A. THERE IS NO CHANGE TO THE OVERALL FORECAST PHILOSOPHY SINCE THE
PREVIOUS PROGNOSTIC REASONING MESSAGE.
   B. TS 09W WILL CONTINUE TO TRACK NORTHWESTWARD THROUGH TAU
12 UNDER THE STR, MAKING LANDFALL NEAR BUSAN WITHIN SIX HOURS. AFTER
TAU 12, IT WILL BEGIN TO ROUND THE STR AXIS AND TURN NORTHWARD THEN
NORTHEAST- TO EAST-NORTHEASTWARD, DRAG ALONG THE EASTERN SOUTH KOREAN
MOUNTAIN RANGE, THEN CROSS THE SEA OF JAPAN (SOJ) BEFORE MAKING
LANDFALL OVER HOKKAIDO BY TAU 72. INCREASING VWS, LAND INTERACTION,
AND COOLING SSTS IN THE SOJ WILL CONTINUE TO RAPIDLY ERODE THE
SYSTEM. CONCURRENTLY, BY TAU 36, IT WILL BEGIN EXTRA-TROPICAL
TRANSITION IN THE SOJ AND MAINTAIN A LARGE WIND FIELD. BY TAU 72, TS
09W WILL BECOME A COLD CORE LOW AFTER IT MAKES LANDFALL IN HOKKAIDO.
NUMERICAL MODEL GUIDANCE REMAINS IN TIGHT AGREEMENT, LENDING HIGH
CONFIDENCE IN THE JTWC FORECAST TRACK.//
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