Tropical Storm FRANCISCO Advisory 8月5日

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 09W (FRANCISCO) WARNING
NR 13//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL STORM (TS) 09W (FRANCISCO), LOCATED APPROXIMATELY 470 NM
EAST-SOUTHEAST OF SASEBO, JAPAN, HAS TRACKED WEST-NORTHWESTWARD AT
16 KNOTS (KTS) OVER THE PAST SIX HOURS. THE LOW LEVEL CIRCULATION
CENTER (LLCC) IS BEING OBSCURED BY A SMALL (ROUGHLY 110 NM WIDE)
CENTRAL DENSE OVERCAST IN ANIMATED ENHANCED INFRARED SATELLITE
IMAGERY WITH DRIER AIR WRAPPING AROUND THE PERIPHERY FROM THE SOUTH.
THERE IS GOOD CONFIDENCE IN THE INITIAL POSITION BASED ON A 041703Z
ATMS 88 GHZ MICROWAVE IMAGE. THE INITIAL INTENSITY OF 50 KTS FALLS
BETWEEN MULTI-AGENCY DVORAK FIXES FROM T3.0-T3.5 (45-55 KTS). THE
ENVIRONMENT IS MARGINALLY FAVORABLE WITH LOW (05-10 KNOTS) VERTICAL
WIND SHEAR (VWS), WARM (28-29 CELSIUS) SEA SURFACE TEMPERATURE
(SST), AND FAIR RADIAL OUTFLOW BEING OFFSET BY DRY AIR ENTRAINMENT
FROM AN AREA OF UPPER-LEVEL CONVERGENCE TO THE SOUTHWEST. TS 09W IS
TRACKING ALONG THE SOUTHERN PERIPHERY OF A SUBTROPICAL RIDGE (STR).
3. FORECAST REASONING.
   A. THERE IS NO CHANGE TO THE OVERALL FORECAST PHILOSOPHY SINCE
THE PREVIOUS PROGNOSTIC REASONING MESSAGE.
   B. THROUGH TAU 36, TS 09W WILL CONTINUE TO TRACK NORTHWESTWARD
AND PASS NEAR SASEBO JUST PRIOR TO TAU 30. ADDITIONALLY, THE SYSTEM
WILL ROUND THE STR AXIS BETWEEN TAU 36 AND 48, MAKE LANDFALL NEAR
BUSAN, KOREA NEAR TAU 40, AND BEGIN EXTRATROPICAL TRANSITION (ETT)
AS IT BEGINS INTERACTING WITH THE MID-LATITUDE BAROCLINIC ZONE
AROUND TAU 72. MODEL GUIDANCE IS IN EXCELLENT AGREEMENT THROUGH TAU
36. AFTER TAU 36, SPREAD REMAINS GOOD BUT BEGINS TO GRADUALLY
INCREASE DUE TO MINOR DIFFERENCES IN THE STRENGTH AND POSITION OF
THE STR. SLIGHT INTENSIFICATION IS EXPECTED UNTIL LANDFALL OVER
KYUSHU AROUND TAU 24. AFTER TAU 24, THE SYSTEM IS EXPECTED TO WEAKEN
DUE TO LAND INTERACTION. HOWEVER, THE CONTINUED FAST FORWARD SPEED
SHOULD MINIMIZE THE AMOUNT OF WEAKENING OVER KYUSHU PRIOR TO PASSING
NEAR SASEBO. BASED ON THE OVERALL EXCELLENT AGREEMENT OF THE MODELS
AND THE STEADY PRESENCE OF THE STR, CONFIDENCE IN THIS PORTION OF
THE JTWC TRACK FORECAST IS HIGH.
   C. AFTER TAU 72, TS 09W WILL CONTINUE TRACKING EAST-NORTHEASTWARD
UNTIL COMPLETING ETT SOMETIME BETWEEN TAU 96 AND 120. THROUGHOUT
THIS PERIOD, COOL SST AND HIGH VWS SHOULD WEAKEN THE SYSTEM. TAKING
INTO ACCOUNT THAT ALONG-TRACK SPREAD IN THE MODEL GUIDANCE TYPICALLY
INCREASES SIGNIFICANTLY AFTER A SYSTEM BECOMES EMBEDDED IN THE MID-
LATITUDE WESTERLIES, THERE IS RELATIVELY GOOD AGREEMENT IN THE
GUIDANCE, MAKING FOR FAIR CONFIDENCE IN THE EXTENDED TRACK
FORECAST.//
NNNN
NNNN