Marine Weather for HS 100


marine weather discussion for N Atlantic Ocean NWS ocean prediction center Washington DC 349 am EDT Tue Apr 24 2018

.Forecast discussion...Major features/winds/seas/significant .Weather for the North Atlantic ocean W of 50w from 30n to 50n.

The GOES-E infrared satellite imagery shows showers along a frontal boundary along the se coast this morning, while the lightning density product shows some embedded tstms in the convection over the srn nt2 offshore waters. Current surface observations show winds up to 40 kt along the se coast, while the ascat wind retrievals from around 0200 UTC last night indicated about the same with the highest winds in the convection. The 00z GFS winds are initialized within 5 kt of the current data this morning, and the model indicates that the front will slowly move E across the area today through Wed as the associated low center moves NE along the coast. The 00z ECMWF is in good agreement with the GFS on the timing and track of the low and front, and indicates gales as well, though slightly weaker than the GFS. The GFS is showing a few areas close to storm force over nt2, mainly over the Gulf Stream later today. The models are all showing a strong low level jet setting up ahead of the front, though the GFS is by far the strongest solution and shows the strongest mixed layer winds in model soundings with winds on the cusp of storm force over the central and srn nt2 later today. However, even the higher resolution regional models such as the arw and nmm are capping sustained winds near 45 kt, and the 00z GFS has trended slightly weaker from the previous run. As a result, confidence with storm force is just below average at this time with the bulk of the guidance keeping sustained winds below storm and the trends in the GFS signalling a weaker solution. However, would not rule out the possibility of higher gusts with the current convective activity ongoing. For the next forecast, am planning on starting out with the 00z GFS 10m winds, favoring the first sigma winds in unstable areas while capping them at 45 kt. Will also continue the mention of higher gusts possible in some of the southern zones. Also planning on maintaining previous gale headlines with above average confidence, but will make some adjustments based on the overall trends noted in the 00z guidance.

The 00z models then indicate a weak high pres ridge will pass quickly across the area Thu night into Fri, before a weaker low pressure system moves through the region later Fri into Sat. There is a fair amount of spread in the model guidance with the overall track and intensity of this next system, and the 00z GFS has trended a little faster from previous runs. The 00z ECMWF/Gem are both to the se of the GFS, while the 00z UKMET is much weaker. The 00z ensemble guidance is showing a slower signal than indicated by the GFS, and is near the previous run which is also close to continuity. Confidence is currently low in the guidance as a result of the large spread, so planning on using a solution that does not diverge much from the previous forecast since no clear trend is evident at this time. For the wind grids, am planning on using the 00z GFS 10m winds exclusively starting from 12z Fri, while time shifting it 6 hour slower to stay near the previous forecast.

.Seas...Sentinel altimeter data from 03z indicated wave heights to 21 ft off the se coast, with the highest near the aforementioned convective activity. The 00z ECMWF wam is initialized much closer to the data than the 00z wavewatch, and builds seas higher than the wavewatch as the current system moves NE across the waters. For the wave heights, am planning on using a 2:1 blend of the ooz ecwmf wam with the 00z wavewatch into 12z Fri, while boosting near the highest winds as they progress NE in the forecast. Will then transition to the 00z wavewatch beyond that point to match the preferred 00z GFS, but will employ same time shift as used with the winds.

.Extratropical storm surge guidance...The 00z estofs is showing a higher positive surge along the se coast today with values near 2 ft in the strong se flow. The models then indicate the surge will continue N along the coast Wed into Thu with values just under a foot over most locations N of Cape Hatteras. The guidance seems reasonable with the expected winds along the coast.


.Nt1 New England waters... .anz810...south of New England... gale Wednesday into Wednesday night. .Anz815...South of Long Island... gale Wednesday.

.Nt2 mid-Atlantic waters... .anz915...Hudson Canyon to the great South Channel... gale Wednesday into Wednesday night. .Anz920...Baltimore Canyon to the great South Channel... gale tonight into Wednesday. .Anz905...The great South Channel to the Hague line... gale Wednesday into Wednesday night. Gale possible Thursday. .Anz910...East of the great South Channel and south of 39n... gale Wednesday into Wednesday night. .Anz825...Inner waters from Baltimore Canyon to Cape Charles Light... gale tonight. .Anz828...Inner waters from Cape Charles Light to Currituck Beach Light... gale today into tonight. .Anz925...Outer waters from Baltimore Canyon to Hatteras Canyon... gale today into Wednesday. .Anz830...Inner waters from Currituck Beach Light to Cape Hatteras... gale today into tonight. .Anz833...Inner waters from Cape Hatteras to Cape Fear... gale today into tonight. .Anz930...Outer waters from Hatteras Canyon to Cape Fear... gale today into tonight. .Anz835...Inner waters from Cape Fear to 31n... gale today. .Anz935...Outer waters from Cape Fear to 31n... gale today into tonight.


.Forecaster Kells. Ocean prediction center.

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