Tropical Storm DOLPHIN Advisory Tue Sep 22

1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.
   TROPICAL STORM 14W (DOLPHIN), LOCATED APPROXIMATELY 551 NM
SOUTH-SOUTHWEST OF YOKOSUKA, JAPAN, HAS TRACKED NORTHWARD AT 08
KNOTS OVER THE PAST SIX HOURS. ANIMATED MULTISPECTRAL SATELLITE
IMAGERY (MSI) DEPICTS PERSISTENT SYMMETRIC CONVECTION ABOUT THE
CORE OF THE SYSTEM WITH FLARING HOT TOWERS CYCLING NEAR THE CENTER
AND SHEARING OFF TO THE NORTHEAST, LEADING TO A SOMEWHAT ELONGATED
CONVECTIVE MASS. THE INITIAL POSITION IS ASSESSED WITH HIGH
CONFIDENCE BASED ON LATE RECEIPT OF A 220013Z METOP-B ASCAT PASS
WHICH CAUGHT THE CENTER ON THE EDGE OF SWATH, WITH THE COINCIDENT
AMSU-B 89 GHZ MICROWAVE IMAGERY PROVIDING ADDITIONAL SUPPORT FOR
THE HIGH CONFIDENCE POSITION. THE INITIAL INTENSITY IS ASSESSED AT
50 KNOTS WITH HIGH CONFIDENCE BASED ON A DVORAK CURRENT INTENSITY
ESTIMATE OF T3.0 FROM PGTW AND RJTD, SUPPORTED BY AN ADVANCED
DVORAK TECHNIQUE (ADT) CURRENT INTENSITY ESTIMATE OF 3.3 (53
KNOTS), A SATELLITE CONSENSUS ESTIMATE OF 47 KNOTS, AND THE
AFOREMENTIONED ASCAT PASS, WHICH SHOWED A SINGLE 50 KNOT WIND BARB
TO THE SOUTHEAST OF THE CENTER, EMBEDDED IN A LARGE AREA OF 45-50
KNOT WINDS. TS DOLPHIN CONTINUES TO EXHIBIT BOTH TROPICAL AND
SUBTROPICAL CHARACTERISTICS. THE THERMAL STRUCTURE REMAINS
TROPICAL WITH A FIRMLY ENTRENCHED WARM CORE ANOMALY IN THE MID-
LEVELS AND THE CONVECTIVE SIGNATURE HAS BECOME MORE SYMMETRIC OVER
THE PAST SIX HOURS. HOWEVER, THE WIND STRUCTURE AND VORTICITY
STRUCTURE IS ASYMMETRIC. THE SYSTEM REMAINS IN A MARGINALLY
FAVORABLE ENVIRONMENT, WITH ROBUST POLEWARD OUTFLOW, STILL TAPPING
INTO THE DIVERGENT UPPER-LEVEL TROUGH THAT HAS NOW MOVED NORTHEAST
OF THE SYSTEM, WITH MODERATE EQUATORWARD OUTFLOW IN PLACE ON THE
EASTERN SIDE OF THE CIRCULATION. UPPER-LEVEL WESTERLIES BEHIND THE
TROUGH ARE PRODUCING SOME PRESSURE ON THE WEST SIDE, IMPINGING
OUTFLOW IN THIS QUADRANT. THE VWS REMAINS LOW AT 10-15 KTS AND
SSTS REMAIN VERY WARM (29-30 DEG C), SERVING TO OFFSET THE
CONVERGENCE ON THE WESTERN SIDE AND ALLOWING FOR SOME
INTENSIFICATION OVER THE PAST SIX HOURS. THE SYSTEM IS CURRENTLY
MOVING NORTHWARD IN A COL AREA BETWEEN A WEAK STR POSITIONED TO
THE EAST AND A SECOND STRONGER STR LOCATED TO THE WEST, WITH THE
EASTERN STR BEGINNING TO BECOME THE DOMINATE STEERING MECHANISM.
3. FORECAST REASONING.
   A. NO CHANGE TO THE FORECAST PHILOSOPHY SINCE THE PREVIOUS
PROGNOSTIC REASONING MESSAGE.
   B. TS DOLPHIN WILL CONTINUE TRACKING NORTHWARD THROUGH TAU 12
ALONG THE WESTERN PERIPHERY OF THE BUILDING STR TO THE EAST, AND
AFTER ROUNDING THE RIDGE AXIS BETWEEN TAUS 12 AND 24, ACCELERATE
ON A NORTHEASTWARD TRACK THROUGH THE END OF THE FORECAST PERIOD.
OVER THE NEXT 12 TO 24 HOURS, THE SYSTEM IS WILL CONTINUE TO TAKE
ON MORE SUBTROPICAL CHARACTERISTICS, BECOMING FULLY SUBTROPICAL BY
TAU 24 AS IT MOVES OVER COOLER WATER, EXPERIENCES INCREASING VWS
AND BEGINS TO ENTRAIN COOLER AND DRIER AIR.  BY TAU 36 THE SYSTEM
WILL BECOME MORE CLOSELY ASSOCIATED WITH THE POLAR FRONT JET,
EXPERIENCE INCREASING VWS AND BEGIN TO DEVELOP FRONTAL
CHARACTERISTICS, TRANSITIONING TO A FULLY EXTRATROPICAL SYSTEM BY
TAU 48 SOUTH OF HONSHU. UPPER LEVEL MASS CONVERGENCE FROM THE
WEST, COMBINED WITH A DECREASE IN THE POLEWARD OUTFLOW AS THE
TROUGH MOVES OUT OF THE AREA, WILL COMBINE TO KEEP THE INTENSITY
STEADY AT 50 KNOTS FOR THE NEXT 12 HOURS. THEREAFTER, THEY SYSTEM
WILL AGAIN TAP INTO THE DIVERGENT QUADRANT OF THE 200 MB JET OVER
HONSHU, INCREASING THE POLEWARD OUTFLOW, WHICH WILL OFFSET COOLER
WATERS AND INCREASING VWS, LEADING TO A SHORT PERIOD OF
INTENSIFICATION THROUGH TAU 48. THEREAFTER, THE SYSTEM WILL
STEADILY WEAKEN AS IT MOVES RAPIDLY OFF THE NORTHEAST AS A STRONG
EXTRATROPICAL SYSTEM. UPON APPROACH TO THE KANTO PLAIN TS 14W IS
EXPECTED TO BE A 40 TO 45 KT EXTRATROPICAL LOW. NUMERICAL MODEL
SOLUTIONS ARE IN MODERATE AGREEMENT THROUGH TAU 48, WITH A 105 NM
SPREAD BETWEEN THE ECMWF AND NAVGEM OUTLIERS AT TAU 48. CROSS
TRACK SPREAD DRASTICALLY INCREASES BY TAU 72 AS SOME TRACKERS
BEGIN TO LOSE THE VORTEX OR JUMP TO A DEVELOPING LOW IN THE SEA OF
JAPAN, LEADING TO A 350 NM SPREAD AT TAU 72. HOWEVER THE MAJORITY
OF THE TRACKERS ARE MORE TIGHTLY PACKED NEAR THE JTWC TRACK. THE
JTWC FORECAST TRACK IS PLACED ALONG THE EASTERN/SOUTHERN SIDE OF
THE TRACKER ENVELOPE THROUGH TAU 36 AND NEAR THE MULTI-MODEL
CONSENSUS THEREAFTER. BASED ON THE TIGHT GROUPINGS IN THE MODEL
TRACKERS, THERE IS OVERALL HIGH CONFIDENCE IN THE JTWC FORECAST
TRACK.//
NNNN
NNNN