marine weather discussion for N Atlantic Ocean NWS ocean prediction center Washington DC 322 PM EST Wed Dec 13 2017
.Forecast discussion...Major features/winds/seas/significant .Weather for the North Atlantic ocean W of 50w from 30n to 50n.
The morning 1500z ascat overpass indicated widespread gales occurring over most of the offshore waters, except for the far southern nt2 waters. These winds align well with the first sigma layer winds from the 12z GFS. Overall, the 12z models are now in very good agreement over the region tonight into early sun. For this time frame we will rely on the 12z GFS winds and use the smart tool which places the higher first sigma layer winds over the unstable areas and slightly lower 10 meter winds over the stable areas right into early sun. We will make a few minor edits to the grids and forecast in deference to nearby coastal WFO and TAFB grids, and also to maintain most of the previous hazards for the afternoon package.
Gales associated with the strong low pressure system moving N from New Brunswick, Canada will diminish over the waters early tonight. A fast-moving clipper-type low pressure system currently over the Midwest will pass E over southern nt1 waters, or near 40n, Thursday morning. Gale to storm force winds are likely with this low pressure system as it crosses the waters later tonight into Thu. The next low pressure system will then impact the waters Fri into Sat with another period of gale force winds likely especially from central nt2 waters N into southern nt1 waters. Any storm force winds with this system will likely occur well E of the waters Fri night. High pressure will then slowly build E toward the region Sat night with gales ending at that time. The high will then pass E over the waters sun, moving off to the E of the area Sun night. For sun into early Mon we will rely on the previous set of grids which used a blend of the 12z ECMWF and 00z ECMWF from yesterday. For most of Mon through the end of the period we will trend the forecast toward the wpc medium range guidance, and adjust the forecast over the next few days, as the 12z guidance from today is in rather poor agreement over the region early next week. We will boost these winds by 10-12 percent or so, as they typically run a little on the low side especially near and S of the Gulf Stream.
Confidence in the forecast is above average tonight into the weekend, and then below average by Sun night through Mon night with the 12z models showing a wide variety of solutions over the region at that time, and beyond.
.Seas...The latest observations over the offshore waters indicate that the previous grids and forecast have initialized the best over the waters, with the 12z ECMWF wam a little too high and the 12z wavewatch running a little too low over the waters. For the afternoon package, we will rely on the previous grids and forecast for tonight, transition to a 50-50 blend of these two wave models Thu into early sun, fall back to the previous grids and forecast later sun and Sun night to match the winds, and then populate with the 12z wavewatch, but make several manual adjustments to fit the wpc wind grids as noted above by Mon and Mon night over the region.
.Extratropical storm surge guidance...No significant issues with the latest surge guidance is noted at this time.
.Nt1 New England waters... .anz800...Gulf of Maine... gale late today into tonight. .Anz805...Georges Bank west of 68w... gale late today into Thursday. Gale possible Saturday. .Anz900...Georges Bank east of 68w... gale late today into tonight. .Anz810...South of New England... gale late today into Thursday. Gale possible Saturday. .Anz815...South of Long Island... gale late today into tonight. Gale possible Saturday.
.Nt2 mid-Atlantic waters... .anz820...Hudson Canyon to Baltimore Canyon... gale late today into Thursday. Gale possible Saturday into Saturday night. .Anz915...Hudson Canyon to the great South Channel... gale late today into Thursday. Gale possible Saturday into Saturday night. .Anz920...Baltimore Canyon to the great South Channel... gale late today into Thursday. Gale possible Saturday into Saturday night. .Anz905...The great South Channel to the Hague line... gale late today into tonight. Storm Thursday. Gale possible Saturday into Saturday night. .Anz910...East of the great South Channel and south of 39n... gale late today into tonight. Storm Thursday. Gale possible Saturday into Saturday night. .Anz825...Inner waters from Baltimore Canyon to Cape Charles Light... gale tonight into Thursday. .Anz828...Inner waters from Cape Charles Light to Currituck Beach Light... gale tonight into Thursday. .Anz925...Outer waters from Baltimore Canyon to Hatteras Canyon... gale tonight into Thursday. Gale possible Friday night. .Anz830...Inner waters from Currituck Beach Light to Cape Hatteras... gale tonight into Thursday. .Anz833...Inner waters from Cape Hatteras to Cape Fear... gale tonight into Thursday. .Anz930...Outer waters from Hatteras Canyon to Cape Fear... gale tonight into Thursday. Gale possible Friday night.
.Forecaster Mills. Ocean prediction center.