Tropical Storm FRANCISCO Advisory 8月3日

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 09W (FRANCISCO) WARNING
NR 05//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL STORM (TS) 09W (FRANCISCO), LOCATED APPROXIMATELY 233 NM
WEST-SOUTHWEST OF MINAMI TORI SHIMA, HAS TRACKED NORTHWESTWARD AT 14
KNOTS (KTS) OVER THE PAST SIX HOURS. THE LOW LEVEL CIRCULATION
CENTER (LLCC) IS BEING OBSCURED BY DEEP CONVECTION IN ANIMATED
ENHANCED INFRARED (EIR) SATELLITE IMAGERY WHICH ALSO SHOWS A LARGE
AREA OF SUBSIDENCE IS INHIBITING CONVECTION TO THE SOUTHWEST OF THE
LLCC. DESPITE THE OBSCURATION IN THE EIR, THERE IS GOOD CONFIDENCE
IN THE INITIAL POSITION, WHICH FALLS BETWEEN THE PGTW AND RJTD
DVORAK FIX POSITIONS. THE INITIAL 40 KT INTENSITY IS HEDGED SLIGHTLY
ABOVE MULTI-AGENCY DVORAK ESTIMATES OF T2.5 (35 KTS) TO REFLECT THE
CONSISTENT STRUCTURE OF THE SYSTEM SINCE A 020747Z SMAP IMAGE SHOWED
A PEAK WIND OF 44 KNOTS. THE ENVIRONMENT IS MARGINAL, DESPITE GOOD
EASTWARD OUTFLOW, WARM (29-30 CELSIUS) SEA SURFACE TEMPERATURE, AND
MODERATE (15-20 KT) VERTICAL WIND SHEAR, DUE TO THE PRESENCE OF A
TUTT CELL TO THE SOUTHWEST THAT IS BRINGING SUBSIDENCE AND SHEAR TO
THAT PORTION OF THE SYSTEM. TS 09W IS TRACKING ALONG THE SOUTHWEST
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. THAT SAID, THE ALONG-
TRACK SPEED HAS INCREASED SLIGHTLY IN THE EARLY TAUS TO REFLECT
RECENT STORM MOTION AND ALIGN WITH THE MODEL CONSENSUS TRACK.
   B. THROUGH TAU 72, TS 09W IS FORECAST TO TRACK GENERALLY
NORTHWESTWARD UNDER THE STEERING INFLUENCE OF THE AFOREMENTIONED
STR. AT TAU 72, SPREAD IN THE MODEL GUIDANCE IS ABOUT 215 NM, THOUGH
SEVERAL MODEL SOLUTIONS ARE CLUSTERED NEAR THE JTWC TRACK FORECAST.
TS 09W SHOULD INTENSIFY SLOWLY THROUGH TAU 36 DUE TO THE CONTINUED
INFLUENCE OF THE TUTT CELL. AFTER TAU 36, THE TUTT CELL IS EXPECTED
TO WEAKEN AND TRACK WESTWARD, ALLOWING TS 09W TO INTENSIFY AT A
FASTER RATE, REACHING 80 KTS AS IT MAKES LANDFALL OVER KYUSHU, JAPAN
AROUND TAU 72.
   C. BEYOND TAU 72, TS 09W WILL GRADUALLY TURN POLEWARD AS IT
STARTS TO ROUND THE STR AXIS. THE SYSTEM WILL WEAKEN SIGNIFICANTLY
AS IT CROSSES KYUSHU DUE TO INCREASED FRICTIONAL EFFECTS. WITH THE
EXCEPTION OF NAVGEM AND GFS, WHICH RECURVE THE SYSTEM SOONER THAN
THE OTHER MEMBERS, MODEL GUIDANCE IS IN FAIR AGREEMENT. OVERALL,
THERE IS FAIR CONFIDENCE IN THE JTWC FORECAST TRACK. //
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