marine weather discussion for N Atlantic Ocean NWS ocean prediction center Washington DC 322 PM EST Tue Dec 12 2017
.Forecast discussion...Major features/winds/seas/significant .Weather for the North Atlantic ocean W of 50w from 30n to 50n.
A complex low pressure system over the eastern Great Lakes and western New England will move NE tonight with an associated strong cold front sweeping E and se over the offshore waters. A 1523z ascat overpass indicated a large area of SW winds up to 30 kt or so over nt2 waters and S and se winds to 25 kts over nt1 waters. There were a couple of 35 kt barbs near the edge of the pass over central nt2 waters which may have been impacted by a few thunderstorms in that region this morning.
Over the short term, we will refresh the grids and forecast using the 12z GFS tonight into Thu night (using the stability tool with places the stronger first-sigma layer winds over the unstable waters and slightly lower 10 meter winds over the stable waters) as it fits the ongoing forecast and latest observations rather well, and is in good agreement with non-GFS models over the next few days. This will lead to gale force winds developing over all offshore waters tonight into Wed, with storm force winds developing over far NE nt2 waters later tonight as the strong front passes E over these waters which are near the north wall of the Gulf Stream. Thunderstorms have become fairly widespread this afternoon and extend from NE nt2 waters or just S of Georges banks SW over the outer portion of the central nt2 waters, E of Cape Hatteras. Thunderstorms will remain likely over this region into tonight near and ahead of the strong cold front. Caution for strong wind gusts near and exceeding gale to storm force and very rough seas in and near the stronger thunderstorms tonight. Conditions will only improve briefly Wed night ahead of the next low pressure system that will impact the waters Thu as it tracks E along 40n or so. This system will allow gales to return to central and northern nt2 waters Thu into Thu night, with a period of storm force winds over NE nt2 waters once again by 18z Thu or so. The 12z GFS backed-off on these winds slightly so we have manually forced them back into the forecast as the 12z GFS may be a little underdone regarding winds over these waters at that time. Confidence levels are somewhat above average over the region tonight through Thu night with decent model agreement through this period.
For Fri through Sat night, we will use a 50-50 blend of the 12z GFS stronger first sigma layer winds and 12z ECMWF guidance over the region, as yet another developing low passes NE over the region. This blend will also tend to maintain gales as was noted in the previous few opc forecasts, with confidence levels near average with gales developing over only nt2 waters Fri night into Sat night. For sun and Sun night, we will transition the offshore forecast toward the 12z ECMWF guidance as high pressure moves E over the waters sun, passing E of the waters Sun night as this solution appears to fit rather well with the latest medium range guidance from wpc. The next cold front will approach the region from the W Sun night. For now, we will keep winds below gale force for Sun night as this is the very end of the forecast package, and we would prefer better model agreement before adding any hazards to the forecast.
.Seas...The latest observations indicate the the 12z wavewatch may be a little too low initially, while the 12z ECMWF wam is a little too high. The previous grids and forecast appear to be close to the initial conditions over the waters this afternoon. For the afternoon package we will rely on the previous grids and forecast for tonight into Thu night, transition to a 50/50 blend of the wavewatch and wam by Fri into Sat night, and then use a 75 percent wam/25 percent wavewatch blend thereafter, as we lowered the winds from the ECMWF guidance late in the period, and this blend will lower the sea heights forecast somewhat which will better match the wind forecast.
.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 tonight into Wednesday night. .Anz805...Georges Bank west of 68w... gale Wednesday into Wednesday night. .Anz900...Georges Bank east of 68w... gale Wednesday into Wednesday night. .Anz810...South of New England... gale tonight into Wednesday night. .Anz815...South of Long Island... gale tonight into Wednesday night.
.Nt2 mid-Atlantic waters... .anz820...Hudson Canyon to Baltimore Canyon... gale tonight into Wednesday. Gale Thursday. .Anz915...Hudson Canyon to the great South Channel... gale tonight into Thursday. Gale possible Saturday. .Anz920...Baltimore Canyon to the great South Channel... gale into Thursday. Gale possible Friday night into Saturday night. .Anz905...The great South Channel to the Hague line... storm tonight. Gale Wednesday into Wednesday night. Storm Thursday. Gale possible Thursday night. Gale possible Saturday into Saturday night. .Anz910...East of the great South Channel and south of 39n... gale late today. Storm tonight. Gale Wednesday into Wednesday night. Storm Thursday. Gale possible Thursday night. 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 late today into Thursday. .Anz925...Outer waters from Baltimore Canyon to Hatteras Canyon... gale late today into Thursday. Gale possible Friday night into Saturday. .Anz830...Inner waters from Currituck Beach Light to Cape Hatteras... gale late today into Thursday. .Anz833...Inner waters from Cape Hatteras to Cape Fear... gale late today into tonight. Gale Wednesday night into Thursday. .Anz930...Outer waters from Hatteras Canyon to Cape Fear... gale late today into Thursday. Gale possible Friday night. .Anz835...Inner waters from Cape Fear to 31n... gale late today into tonight. .Anz935...Outer waters from Cape Fear to 31n... gale late today into tonight. Gale possible Friday night.
.Forecaster Mills. Ocean prediction center.