08W(AMPIL) forecast to intensify significantly next 72H//07W(SON-TINH)//09W//06W(MARIA)//05L(ERNESTO) 1303utc

JTWC IS ISSUING 6HOURLY WARNINGS ON 07W, 08W, 09W. 3HOURLY SATELLITE BULLETIN ARE ISSUED ON THE REMNANTS OF 06W, ON 07W, 08W, 09W.

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION: ANIMATED MULTISPECTRAL SATELLITE IMAGERY (MSI) DEPICTS A STILL VERTICALLY TILTED VORTEX, WITH THE LLCC LOCATED NEAR THE NORTHERN EDGE OF THE MASS OF DEEP THUNDERSTORMS. VISIBLE IMAGERY SUGGESTS THAT THE TILT IS ABOUT 40 NM, AND THAT THE VORTEX IS NOW PRECESSING, WITH THE TILT NOW MORE SOUTHWARD COMPARED TO SOUTHWESTWARD SIX HOURS AGO. THE PRECESSION COULD BE CONTRIBUTING TO THE TEMPORARY SLOWDOWN IN FORWARD MOTION OVER THE PAST FEW HOURS. THE OVERALL SATELLITE PRESENTATION HAS NOT CHANGED MUCH, SO THE INTENSITY IS HELD AT 40 KT. THE CENTER OF CIRCULATION IS PASSING WEST OF IWO TO, WHERE OBSERVED SUSTAINED WINDS HAVE NOT YET EXCEEDED 16 KT. HEALTHY EQUATORWARD OUTFLOW ALOFT IS NOTED, WITH POLEWARD OUTFLOW A LITTLE WEAKER THAN SIX HOURS AGO.

FORECAST REASONING. SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO THE FORECAST FROM THE PREVIOUS WARNING. FORECAST DISCUSSION: TROPICAL STORM 08W (AMPIL) IS TRACKING NORTHEASTWARD ALONG THE SOUTHERN RIM OF THE LARGE-SCALE MONSOON GYRE PATTERN IN THE NORTHWEST PACIFIC. AMPIL'S CIRCULATION IS VERTICALLY TILTED DUE TO LIGHT NORTHEASTERLY SHEAR, CAUSED BY NEAR-CALM UPPER-LEVEL WINDS OVERLAYING SOUTHWESTERLY LOWER-LEVEL BACKGROUND FLOW. LIGHT TO MODERATE NORTHEASTERLY OR NORTHERLY SHEAR IS EXPECTED TO PERSIST FOR 36-48 HOURS, WHICH MAY DAMPEN THE STORM'S RATE OF ORGANIZATION, BUT IS NOT STRONG ENOUGH TO PREVENT INTENSIFICATION. THE GFS, HAFS-A, AND ECMWF MODELS INITIALIZED THE VORTEX TILT WELL, AND AGREE ON GRADUAL ALIGNMENT OF THE VORTEX DURING THE NEXT 24-48 HOURS. THE EXACT TIMING OF THIS ALIGNMENT WILL DETERMINE THE PACE OF INTENSIFICATION FOR THE FIRST 48 HOURS, WITH QUICKER ALIGNMENT LEADING TO QUICKER INTENSIFICATION AND VICE VERSA. THE JTWC FORECAST FOLLOWS A CLIMATOLOGICAL INTENSIFICATION RATE IN THE SHORT-TERM, BRINGING AMPIL TO 75 KT IN 48 HOURS AS IT TRACKS WITHIN 130 NM NORTHWEST OF THE ISLAND OF IWO TO. AFTER 48 HOURS, AMPIL WILL INTERACT WITH A DECAYING UPPER-LEVEL LOW (ULL) SOUTHEAST OF HONSHU IN A WAY THAT WILL REDUCE VERTICAL SHEAR AND POTENTIALLY CAUSE FAVORABLE SUPERPOSITION OF THE ULL WITH THE STORM. THIS ENVIRONMENTAL EVOLUTION, COUPLED WITH PASSAGE OVER 30-31 DEGREE CELSIUS SEA SURFACE TEMPERATURES THAT ARE RUNNING 2-3 CELSIUS WARMER THAN CLIMATOLOGY, SHOULD LEAD TO AN INCREASE IN THE INTENSIFICATION RATE BETWEEN 48 AND 72 HOURS. THE JTWC FORECAST BRINGS AMPIL TO A PEAK INTENSITY OF 100 KT BY 72 HOURS. DURING THE 36-72 HOUR PERIOD, THE TRACK IS EXPECTED TO BEND TOWARD THE NORTH AS AMPIL PRESSES AGAINST THE WESTERN PERIPHERY OF A DEEP-LAYER STEERING RIDGE EAST OF JAPAN. MODELS ARE IN GOOD AGREEMENT THAT THIS RIDGE WILL BE CENTERED NEAR THE LATITUDE OF TOKYO DURING THIS TIME, LEADING TO A NEAR-NORTHWARD STEERING CURRENT UNTIL THE STORM REACHES THE SAME LATITUDE. THIS COULD BRING AMPIL CLOSE TO OR OVER HONSHU BEFORE IT TURNS NORTHEASTWARD AROUND THE RIDGE AND INTO THE JET STREAM. THERE REMAINS SIGNIFICANT UNCERTAINTY AS TO WHETHER AMPIL WILL MAKE LANDFALL IN JAPAN, LARGELY DUE TO TRACK UNCERTAINTY IN THE FIRST 48 HOURS CAUSED BY THE VORTEX ALIGNMENT PROCESS. THE JTWC FORECAST TAKES AMPIL CLOSE TO THE COASTLINE OF CHIBA PREFECTURE AS A STRONG TYPHOON. PLEASE NOTE THAT THE POINT OF CLOSEST APPROACH TO JAPAN CURRENTLY FALLS BETWEEN TWO FORECAST POINTS NEAR THE APEX OF TRACK CURVATURE, AND THUS THE STORM MAY PASS CLOSER TO JAPAN THAN THE INTERPOLATED FORECAST TRACK DEPICTS. AFTER 96 HOURS, AMPIL WILL INTERACT WITH THE MID-LATITUDE JET AND BEGIN EXTRATROPICAL TRANSITION WHILE TURNING NORTHEASTWARD OVER COOLER WATERS.

MODEL DISCUSSION: DYNAMICAL MODELS ARE GRADUALLY COMING INTO CLOSER AGREEMENT ON THE TRACK THROUGH 72 HOURS. THE JTWC FORECAST LEANS CLOSE TO A CONSENSUS OF THE GFS, GFS ENSEMBLE MEAN, ECMWF, ECMWF ENSEMBLE MEAN, AND HAFS-A. THE JTWC INTENSITY FORECAST IS CLOSE TO THE MULTI-MODEL CONSENSUS THROUGH 48 HOURS, BUT HIGHER THAN THE CONSENSUS BETWEEN 48 AND 96 HOURS, SHOWING A PEAK INTENSITY CLOSER TO THE PREDICTIONS OF HAFS-A, HWRF, COAMPS-TC, AND GFS THAN SOME OF THE WEAKER STATISTICAL MODELS.