marine weather discussion for N Atlantic Ocean NWS ocean prediction center Washington DC 1011 PM EDT Thu Apr 25 2019
.Forecast discussion...Major features/winds/seas/significant .Weather for the North Atlantic ocean W of 50w from 30n to 50n.
GOES infrared satellite imagery shows a weak warm front across the nrn nt2 offshore waters this evening, and a strong low pressure system inland over the ern conus. Ascat wind retrievals from 15z earlier today indicated no more than about 15 kt in the offshore waters with the weak warm front and a high pressure ridge to its N, and current surface reports show about the same. The 18z/12z models show the winds slowly increasing in the nt2 waters tonight into Fri as the strong system to the W approaches the area. The models generally agree on the timing of the boundary, and increase the winds in the southerly flow ahead of it with a strong low level jet setting up ahead of it. The guidance has a fairly strong signal for gales developing the southerly flow in the less stable conditions over warmer SSTs, while the GFS has been showing a weak potential for a brief period of storm force embedded within the gales on Fri night. NAM and GFS model soundings both indicate mixed layer winds greater than 50 kt, so there is some support for the storm headlines. However, the bulk of the 12z guidance remains below storm, so confidence is low with anything 48 kt or higher. Confidence with the adjacent gales are well supported, so confidence is well above average with the previous headlines which were based on the GFS gales. As a result, am planning on making only minor adjustments for the pre-frontal headlines. The models then show gales again in the cold advection behind the front, and this has been consistent for the past few days now. As a result of the good agreement of the models on the previous gale headlines, am planning on staying near the previous headlines into Sat.
The models indicate the strongest winds associated with the previously mentioned low pressure system will move E of the area Sat night, before a second system passes E across the nt1 and nrn nt2 waters sun and Sun night. The models show an area of marginal gales with this second system in the offshore waters, with the highest again ahead of the cold front. However, this next system takes a more northerly track, and has less interaction with the Gulf Stream. As a result, confidence with the winds reaching gale force is just below average as a result of the weak signal, so planning on continuing with no warning headlines. Otherwise, the GFS indicates that the subsequent systems will weaker through the medium range period, though some differences on the timing and track develop between the models. As a result, will stay near continuity for the remainder of the forecast.
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For the wind grids, will lean towards the 12z GFS with some minor adjustments through the end of the forecast period Tue night.
Models coming into agreement with strength of southerly flow ahead of a strong cold front to affect the offshore waters Fri into Sat. GFS/UKMET/ECMWF in good agreement with gales in the nt2 offshore waters, and confidence in gales in the nt2 waters ahead of the front is high at this time. GFS hinting at possibility of a few storm force winds popping up in the northern nt1 waters Fri night in the warmer waters of the Gulf Stream, with even GFS 10m winds showing a few storm force winds. UKMET/ECMWF not that strong in the southerly flow, but still hinting at 40 to 45 kt possible. Not confident enough to introduce storm force winds into the forecast at this time, and will raise winds to 45 kt in this package but will need to be watched over the next run or two and if these higher trends continue, storm warnings may need to be issued. Models trending higher with winds in portions of the nt1 waters Fri night into Sat and will introduce brief period of gales for this time period. GFS was stronger with winds as it was showing around 40 kt, but will limit winds to 35 kt in the nt1 waters at this time with moderate confidence. As for the winds behind the front, continue with gales in the northern nt2 waters in the westerly flow as models continue to show unstable conditions behind the front due to cold air advection.
Guidance in fairly good agreement with the timing and strength of next system to affect the region sun and Sun night. GFS may be a bit too slow with the system, but only by about 3 or 6 hours. Models do agree with 30 kt in the southerly flow ahead of the system, with the GFS trying to squeeze some 35 kt winds as it exits the northern nt2 waters Sun night. Will keep any gales associated with this system east of the offshore waters for now and limit winds to 30 kt.
Another system moves across the northern offshore waters Tue and Tue night, but is weaker than previous systems with winds to 25 kt expected.
.Seas...For the wave grids, will lean towards 12z wna wavewatch through the forecast period.
.Extratropical storm surge guidance...N/A.
.Nt1 New England waters... .anz800...Gulf of Maine... gale Friday night into Saturday. .Anz805...Georges Bank west of 68w... gale Friday night. .Anz900...Georges Bank east of 68w... gale Friday night into Saturday. .Anz810...South of New England... gale Friday night.
.Nt2 mid-Atlantic waters... .anz915...Hudson Canyon to the great South Channel... gale Friday night into Saturday. .Anz920...Baltimore Canyon to the great South Channel... gale Friday night into Saturday. .Anz905...The great South Channel to the Hague line... gale Friday night into Saturday. .Anz910...East of the great South Channel and south of 39n... gale Friday night into Saturday. .Anz825...Inner waters from Baltimore Canyon to Cape Charles Light... gale Friday into Friday night. .Anz828...Inner waters from Cape Charles Light to Currituck Beach Light... gale Friday into Friday night. .Anz925...Outer waters from Baltimore Canyon to Hatteras Canyon... gale Friday into Saturday. .Anz830...Inner waters from Currituck Beach Light to Cape Hatteras... gale Friday into Friday night. .Anz833...Inner waters from Cape Hatteras to Cape Fear... gale Friday into Friday night. .Anz930...Outer waters from Hatteras Canyon to Cape Fear... gale Friday into Friday night. .Anz835...Inner waters from Cape Fear to 31n... gale Friday into Friday night. .Anz935...Outer waters from Cape Fear to 31n... gale Friday night.
.Forecaster Kells/achorn. Ocean prediction center.