Marine Weather for HS 100


marine weather discussion for N Atlantic Ocean NWS ocean prediction center Washington DC 921 am EST Tue Feb 19 2019

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

The GOES visible satellite imagery shows cold air cumulus streaming across the offshore waters this morning in the wake of rapidly intensifying low pressure system now well E of the offshore waters. As noted below, the ascat overpasses indicated gale force winds across the outer offshore waters last night, but the system has moved much further E from the time of the pass taking the stronger winds with it. Current surface observations show winds up to 24 kt in the nrn offshore waters, and the GFS/ECMWF both indicate the winds decreasing in the nrn zones today as high pressure builds over the waters. Further S, the latest NCEP surface analysis shows a stationary front just S of the offshore waters interacting with the aforementioned high pressure building across the area. Current surface reports show winds up to 25 kt along the se coast in the tightening pressure gradient, and the models show the winds continuing at that intensity toady and tonight as the front drifts N into the area while low pressure develops to the W. The GFS/ECMWF are then in somewhat good agreement on a coastal low forming along the front and moving NE along the coast as the inland low approaches the coast while pulling another cold front towards the area. The models are in reasonably good agreement on the timing and intensity of the features, though the GFS is a bit stronger with the winds, mainly over the Gulf Stream. The GFS is showing close to storm in the outer nt2 waters on Thu, while the ECMWF indicated marginal gales. The previous forecast used a compromise solution and had up to 40 kt, and this seems reasonable given the level of model support. As a result, am planning on only minor changes with confidence above average on the gale headlines.

The models then show the gales ending in the offshore waters Thu night as the front moves E of the area. Another high is expected to build over the waters Fri before another low moves over the area Sat. Overall, the GFS/ECMWF agree fairly well on the features, though GFS continues to run a bit stronger with the winds in the offshore waters with the system on Sat indicating a few gales with it. However, the rest of the models are a little weaker, so confidence with gales on Sat is below average for right now. The previous forecast capped winds at 30 kt, and this still seems like a decent compromise so will continue along those lines in the update package.

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Ascat overpasses from last evening did show gale force winds occurring over the outer portion of the northern nt2 waters, S and se of Georges Bank. These winds matched-up quite well with the current opc wind grids over the region. Rapidly intensifying low pressure about 250 nm S of Newfoundland island at 06z this morning will continue to move E away from the region today as high pressure builds E from the Midwest and Great Lakes. The high will reach the coast early tonight, then cross the waters tonight into Wed. A low pressure system will approach from the W and SW by later Wed as a frontal boundary develops near the se and mid-Atlantic coasts. Overall, the 00z models are in good agreement over the region today through Wed. We will populate grids with a 50/50 blend of the previous grids, and 00z namnest winds, which will result in little change from the past few opc forecasts, and confidence levels remaining above average through Wed.

For Wed night, we expect low pressure to form and lift N along the coastal front as the main low crosses the Great Lakes. Southerly winds will likely increase especially over waters near and S of the Gulf Stream Wed night, or similar to the previous opc forecast. Thunderstorms may also develop by Wed night, mainly off the se and southern mid-Atlantic coasts, with the potential for very gusty winds and rough seas near the heavier thunderstorms. For Thu, we expect the coastal low to strengthen and turn E over New England waters with an associated trailing cold front passing E over the region. The threat for gales will persist in advance of and just in the wake of the front as it crosses the waters Thu with the highest chance for gales near and S of the north wall of the Gulf Stream. For Thu night, we expect the gales to shift E of the waters as the intensifying low moves further E away from the waters and high pressure builds E from the Midwest and Great Lakes. The high will then move E over the waters Fri into Sat with improving conditions expected for most areas at that time. The high will then shift E of the waters Sat night as a warm front lifts N over nt2 waters. Overall, the 00z models have remained quite consistent and are in generally good agreement on the above scenario expected to develop over the region for the next few days. For the early morning package, we will use a 50/50 blend of the previous grids and 00z ECMWF winds for Wed night through Fri, and then trend the forecast more toward the consistent 00z ECMWF winds for Fri night through Sat night. Forecast confidence is near to above average over the waters Wed night into Sat night.

Seas...both the 00z wavewatch and 00z ECMWF wam appear to have initialized fairly well over the offshore waters according to the latest observations and altimeter data, with the 00z wavewatch running up to 1 to 2 ft too low mainly over the inner waters off the New England and mid-Atlantic coasts. For the early morning package we will use a 50/50 blend of the previous sea heights and 00z wam sea heights for today through Fri to best match the wind forecast, and then transition the gridded forecast more toward the 00z wam Fri night through Sat night over the waters.

.Extratropical storm surge guidance...With the coastal front setting up off the Georgia and Carolina coasts by later today and tonight, and generating some enhanced east to northeast winds, there is potential for some minor to potentially moderate surge from Charleston to northeast Florida. The estofs is once again showing values around 1 to 1.5 ft tonight, with the etss 1 ft and below. A positive surge will likely expand N along the coast Wed through early Thu, before offshore winds develop over all areas by Thu afternoon. The higher estofs values seem reasonable based on the latest wind forecast. With good model agreement over the region we see no need to deviate significantly from the latest surge guidance. For more details please monitor the latest forecast and information from your local National Weather Service office.


.Nt1 New England waters... None.

.Nt2 mid-Atlantic waters... .anz920...Baltimore Canyon to the great South Channel... gale Wednesday night. Gale possible Thursday. .Anz905...The great South Channel to the Hague line... gale possible Thursday into Thursday night. .Anz910...East of the great South Channel and south of 39n... gale possible Thursday into Thursday night. .Anz925...Outer waters from Baltimore Canyon to Hatteras Canyon... gale Wednesday night. Gale possible Thursday. .Anz830...Inner waters from Currituck Beach Light to Cape Hatteras... gale Wednesday night. .Anz833...Inner waters from Cape Hatteras to Cape Fear... gale Wednesday night.


.Forecaster Kells/Mills. Ocean prediction center.

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