Tropical Storm SIX Advisory Tue Aug 11

MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TROPICAL STORM 06W (SIX)
WARNING NR 007//
RMKS//
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL DEPRESSION 06W (SIX), LOCATED APPROXIMATELY 109 NM NORTH
OF IWO TO, HAS TRACKED WESTWARD AT 12 KNOTS OVER THE PAST SIX HOURS.
ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A FULLY
EXPOSED LOW LEVEL CIRCULATION CENTER (LLCC) WITH FLARING CONVECTION
SHEARED TO THE EAST OF THE LLCC. THE INITIAL POSITION IS PLACED WITH
HIGH CONFIDENCE BASED ON THE EXPOSED LLCC IN THE VISIBLE SATELLITE
IMAGERY. THE INITIAL INTENSITY OF 25 KNOTS IS ASSESSED WITH HIGH
CONFIDENCE BASED ON DVORAK CURRENT INTENSITY ESTIMATES OF T1.5 (25
KNOTS) FROM BOTH PGTW AND RJTD, AND A RAW ADT ESTIMATE OF 1.5. TD 06W
REMAINS IN A VERY MARGINAL ENVIRONMENT WITH MODERATE TO STRONG (20-25
KNOTS) VWS, HIGH SSTS NEAR 30 DEG C AND WEAKLY DIVERGENT UPPER-LEVEL
OUTFLOW. TD 06W CONTINUES TO TRACK WESTWARD ALONG THE SOUTHERN
PERIPHERY OF A DEEP-LAYER STR LOCATED TO JUST SOUTHEAST OF TOKYO.
3. FORECAST REASONING.
   A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS
PROGNOSTIC REASONING MESSAGE.
   B. TD 06W WILL CONTINUE TRACKING WESTWARD ALONG THE SOUTHERN
PERIPHERY OF THE STR THROUGH TAU 24 BEFORE TURNING MORE WEST-
SOUTHWEST AS THE SYSTEM WEAKENS, COMING UNDER THE INFLUENCE OF THE
LOWER LEVEL FLOW PATTERN. BY TAU 72, THE SYSTEM WILL LIE BETWEEN
OKINAWA AND MINAMI DAITO JIMA, HAVING SLOWED SIGNIFICANTLY AS IT
APPROACHES A WEAK STEERING ENVIRONMENT INDUCED BETWEEN SUBTROPICAL
RIDGES TO THE NORTHEAST AND NORTHWEST. INTENSITY IS FORECAST TO
REMAIN FLAT THROUGH TAU 48 UNDER THE COMPETING INFLUENCES OF HIGH
SSTS AND MODERATE WESTWARD OUTFLOW OFFSET BY MODERATE TO STRONG VWS.
THERE LIKELY WILL BE SHORT DURATION FLUCTUATIONS ABOVE AND BELOW 25
KNOTS AS CONVECTION FLARES AND DISSIPATES, BUT OVERALL INTENSITY WILL
REMAIN STEADY THROUGH TAU 48. AFTER THIS POINT AND THROUGH TAU 72,
THE SYSTEM WILL BEGIN DISSIPATING AS VWS BECOMES DOMINANT OVER THE
OUTFLOW.
   C. BY TAU 96, TD 06W IS FORECAST TO SLOW, BECOMING NEARLY QUASI-
STATIONARY SOUTH OF OKINAWA UNDER THE INFLUENCE OF A WEAK LOW-LEVEL
STEERING PATTERN. AT THE SAME TIME, TD 06W IS EXPECTED TO CONTINUE
WEAKENING AS A TROPICAL CYCLONE BY TAU 96 AS INCREASING VWS AND LACK
OF UPPER-LEVEL OUTFLOW WILL COMBINE TO  DISSIPATE THE SYSTEM BY TAU
96 JUST SOUTH OF OKINAWA NUMERICAL MODEL GUIDANCE ALL AGREE ON THE
GENERAL FORECAST, BUT DIFFER IN THE EXACT TRACK, WITH A 100 NM SPREAD
AT TAU 48, WITH SPREAD ABOUT 150 NM BY TAU 96. THE OFFICIAL JTWC
FORECAST LIES TO THE NORTH OF THE MULTI-MODEL CONSENSUS, CLOSER TO
THE GROUPING OF JGSM, ECMWF AND UKMO MODEL TRACKERS. DUE TO THE
MODERATE SPREAD IN THE MODEL SOLUTIONS, THERE IS FAIR CONFIDENCE IN
THE JTWC FORECAST TRACK.//
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