marine weather discussion for N Atlantic Ocean NWS ocean prediction center Washington DC 855 PM EST Sat Feb 24 2018
.Forecast discussion...Major features/winds/seas/significant .Weather for the North Atlantic ocean W of 50w from 30n to 50n.
The NCEP surface analysis indicates a weak stationary front across the offshore waters, and a high pres ridge to the N over New England with a Second Ridge to the S across the srn nt2 offshore waters. Current surface observations indicate generally 15 kt or less over the offshore waters, except over the ern Gulf of Maine where winds are still being reported up to 25 kt in some remaining cold advection over anomalously warm SSTs. The 18z GFS and 12z ECMWF/UKMET/NAM/Gem winds were all initialized about 5 kt low in the cold advection, which is not surprising with the low bias the models have had this winds with cold advection, especially with the warmer SSTs in the W Atlc. The previous forecast started out with 25 kt at 00z, then decreased them later tonight as the models all indicate the cold advection will move E of the area. The models then indicate stationary front across the nrn nt2 waters will start lifting N as a warm front on sun, ahead of a shortwave trough moving into the ern conus. The models all indicate an increase in the winds between the warm front and the departing ridge, with the GFS consistently indicating gales across the Gulf of Maine for several days now. Most of the models are indicating at least 30 kt, so confidence in the previous gale headlines for sun into Sun night remains near average. Planning on continuing previous headlines as a result.
The models then remain in good overall agreement through Tue, before the GFS/Gem become slower with a weak system through the Gulf of Maine on Wed. The 12z ECMWF/UKMET are a touch faster, which was preferred by the previous forecast. As a result of the model spread, confidence in any one solution is low right now, so planning on staying near continuity. However, the 12z/18z models come back into good agreement on Thu, with a much stronger system expected to move into the wrn Atlc. The GFS/Gem/UKMET/ECMWF all indicate a strong cold front will move offshore, and generally agree well on it despite some minor timing differences. They also agree on the track of the low, which is now shown to exit the nrn mid Atlc coast on Thu night. In addition, the models are all indicating at least gale force winds winds will develop ahead of this system, as a strong low level jet is forecast to develop just ahead of the front with GFS/ECMWF 925 mb winds indicating up to 75 kt over nt1 by Thu night. The GFS has been indicating storm force over nt1 by Thu night, but confidence is somewhat low as a result of the forecast range and the lack of support from the rest of the models. However, confidence with minimal gale force winds is above average as a result of the strong consensus. As a result, planning on adding gales to the update package for Thu night, and will generally populate with the 12z ECMWF from Tue night Onward.
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Current conditions...the 12z NCEP surface analysis shows a 1007 mb low centered about 200 nm E of Cape Sable, with a cold front extending SW from the low towards zone 910 in the NE part of the nt2 area, and a warm front extending S from the low into the waters E of 60w. The analysis shows a warm front extending roughly W to E across the northern nt2 waters. The analysis also indicates high pressure ridging over the central and southern nt2 waters associated with a 1028 high centered E of the nt2 area near 32n69w. Latest ascat and ascat hi-res passes from a few hours ago show 20 to 30 kt winds in W to NW flow over the eastern part of Georges Bank and in the far NE part of the nt2 waters.
Models/forecast...the frontal low pressure system will move off to the E this evening while strengthening. A warm front will move off the mid Atlantic coast sun. A developing low will move NE over the nt1 area late sun and Sun night, then move off to the NE Mon while strengthening. Another warm front will shift E across the nt1 area Wed and Wed night. The medium range models are in good overall agreement across the offshore waters for tonight through Tue, with only a few minor intensity differences noted, so will use the previous wind grids which are bases on a 50/50 blend of the 00z ECMWF/GFS during this timeframe in order to smooth out the intensity differences, with the blend boosted upwards 15 percent for sun and Sun night to enhance the se flow over the Gulf of Maine and Georges Bank zones. The GFS becomes somewhat of an outlier solution later in the forecast period, since it is the only model to bring a cold front se over the nt1 waters on Wed and Wed night. So will use the more representative 00z ECMWF for Tue night through the rest of the forecast period. Have average confidence in the Gale Warning in the nt1 waters for sun and Sun night.
Seas...both the ECMWF wam and wavewatch initialized within one or two feet of the most recent observations in the offshore waters, although the wavewatch has been a bit underdone with the seas in the outer zones of the northern nt2 waters. However, the models are in good agreement through Tue in the offshore waters, so will go with the previous wave height grids, which are based on a 50/50 blend of the 00z ECMWF wam/wavewatch for this timeframe to smooth out some minor differences. Then will go exclusively with the 00z ECMWF wam for Tue night through the rest of the forecast period, in order to match up with the preferred 00z ECMWF wind grids.
Extratropical storm surge guidance...the models indicate E to se flow in the 20 to 30 kt range ahead of a warm front over the nt1 area on sun. Estofs has a pos surge in the 1.0 to 1.5 ft range along the New Jersey and New England coasts for sun into Sun night, while etss is a notch lower with a positive surge in the 0.5 to 1.0 ft range. Continue to belive that the etss is a bit underdone with the strength of this surge.
.Nt1 New England waters... .anz800...Gulf of Maine... gale Sunday into Sunday night. Gale possible Thursday night. .Anz805...Georges Bank west of 68w... gale Sunday. Gale possible Thursday night. .Anz900...Georges Bank east of 68w... gale Sunday into Sunday night. Gale possible Thursday night. .Anz810...South of New England... gale possible Thursday night. .Anz815...South of Long Island... gale possible Thursday night.
.Nt2 mid-Atlantic waters... .anz915...Hudson Canyon to the great South Channel... gale possible Thursday night. .Anz920...Baltimore Canyon to the great South Channel... gale possible Thursday night. .Anz905...The great South Channel to the Hague line... gale possible Thursday night. .Anz910...East of the great South Channel and south of 39n... gale possible Thursday night. .Anz828...Inner waters from Cape Charles Light to Currituck Beach Light... gale possible Thursday night. .Anz925...Outer waters from Baltimore Canyon to Hatteras Canyon... gale possible Thursday night. .Anz830...Inner waters from Currituck Beach Light to Cape Hatteras... gale possible Thursday night. .Anz833...Inner waters from Cape Hatteras to Cape Fear... gale possible Thursday night. .Anz930...Outer waters from Hatteras Canyon to Cape Fear... gale possible Thursday night. .Anz835...Inner waters from Cape Fear to 31n... gale possible Thursday night. .Anz935...Outer waters from Cape Fear to 31n... gale possible Thursday night.
.Forecaster Kells/Scovil. Ocean prediction center.