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000 AGNT40 KWNM 231936 MIMATN Marine Weather Discussion for N Atlantic Ocean NWS Ocean Prediction Center Washington DC 336 PM EDT Mon Oct 23 2017 .FORECAST DISCUSSION...Major features/winds/seas/significant .weather for the North Atlantic Ocean W of 50W from 30N to 50N. The latest GOES water vapor satellite imagery shows a vigorous shortwave trough inland over the SE CONUS moving to the E. The latest NCEP surface analysis indicates the associated surface low pres system just E of the upper trough, and the Ascat from 14Z indicated winds up to 20 kt in the SE flow ahead of the approaching system in the srn and central NT2 offshore waters. However, the Ascat missed areas right along the SE coast, and recent surface reports show winds up to 20 kt and up to 25 kt just W of the offshore waters. The 12Z GFS/ECMWF 10m/surface winds are initialized well when compared with the current data, and the models indicate the winds will increase in the offshore waters tonight into Tue night as the front is expected to approach to the coast and increase the pressure gradient from the interaction with high pres E of the offshore waters. The 12Z models are all indicating at least marginal gales by late Tue night, mainly in the unstable environment over the Gulf Stream. The models are also indicating a small area of gales extending into NT1 by Wed as both the 12Z GFS/ECMWF show a strong low level jet setting up ahead of the front with 925 mb winds in the 60 to 65 kt range. The vertical wind speed shear should induce some turbulent mixing, and should be enough to mix gales down to the surface for at least a brief period. Confidence in gales for NT2 is high as a result of the less stable environment, and about average for NT1 as the strong low level jet should be enough to break through the stable boundary layer over the cold shelf waters with SSTs currently in the upper 50s to low 60s. For the wind grids, am planning on starting out with the 12Z GFS 10m winds into 12Z Wed, but will use first sigma winds in unstable areas to account for the deeper mixed boundary layer. In the medium range, the 12Z models all indicate the aforementioned front will pass E of the offshore waters by Thu night. The 12Z GFS has trended a little faster with the timing, while the 12Z ECMWF is a tad slower. The models also differ on the timing of a low developing along the front to the E of the area, and the 12Z GFS becomes a northerly outlier with the track. The 12Z ECMWF is supported a bit better by the rest of the 12Z guidance, so planning on transitioning to the 12Z ECMWF at 12Z Wed. The models also indicate another low, possibly a tropical cyclone, will move into the srn waters on Sat. However, there is quite a bit of spread on the track, and not much of a consensus between the models. As a result, will continue with the 12Z ECMWF through the remainder of the forecast period, but confidence is somewhat low. Seas...The 12Z Wavewatch and ECMWF WAM both initialized well over the offshore waters, and are in good agreement through Tue night. As a result, am planning on using a 50/50 blend of the two solutions as a compromise. Will then transition to the 12Z ECMWF WAM to reflect the trends of the preferred 12Z ECMWF winds. .Extratropical Storm Surge Guidance...N/A. .WARNINGS...Preliminary. .NT1 New England Waters... .ANZ800...Gulf of Maine... Gale Wednesday. .NT2 Mid-Atlantic Waters... .ANZ920...Baltimore Canyon to the Great South Channel... Gale Tuesday night into Wednesday. Gale Possible Wednesday night. .ANZ905...The Great South Channel to the Hague Line... Gale Possible Thursday. .ANZ910...East of the Great South Channel and south of 39N... Gale Tuesday night into Wednesday. Gale Possible Wednesday night into Thursday. .ANZ925...Outer Waters from Baltimore Canyon to Hatteras Canyon... Gale Wednesday. .ANZ930...Outer Waters from Hatteras Canyon to Cape Fear... Gale Tuesday night. $$ .Forecaster Kells. Ocean Prediction Center.

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