marine weather discussion for N Atlantic Ocean NWS ocean prediction center Washington DC 344 PM EDT Mon Mar 27 2017
.Forecast discussion...Major features/winds/seas/significant .Weather for the North Atlantic ocean W of 50w from 30n to 50n.
The latest GOES visible satellite imagery indicates an area of high pres in the W Atlc to the east of the offshore waters and a warm front across nrn nt2 and srn nt1. Ascat wind retrievals from 15z this morning indicates winds to 25 kt in the Gulf of Maine ahead of the warm front. The ascat and imagery also shows a second weak across the srn nt2 waters. The 12z GFS 10m winds are initialized well when compared with the current data, although a tad high across the Gulf of Maine in some locations. The GFS indicates that the front will lift north tonight as low pres develops along the boundary. The 12z models all indicate the system will slowly strengthen, and all show winds remaining below gale force as is moves through the area this evening. The GFS is a bit stronger with the winds as it moves east of the area...with gales developing S of Nova Scotia late tonight into Tue. The previous forecast kept winds below gale force and used 10m GFS winds in the stable environment over nt1. This still looks good, so planning on starting out with the 12z GFS in the next forecast. In addition, the lightning density product indicates a few isolated tstms over the Gulf Stream in nrn nt2. Will add mention to zone anz910 of isolated showers and tstms as a result.
The 12z models are in decent agreement over the short range, though there are a few minor differences with the next low off the coast on Tue night into Wed. The 00z GFS had been slightly faster than the 00z ECMWF with moving the low through the area, but the 12z run trended slower and is now in better agreement with the 12z ECMWF and the rest of the 12z guidance. The 12z GFS also indicates an area of strong cold air advection in the wake of the cold front across the outer waters of nrn nt2 and nt1. The GFS has been indicating a brief period of gales in the cold advection on Thu, and the 12z ECMWF/NAM/Gem all indicate about the same. Only the 12z UKMET is not showing gales, and indicates Max winds of 25 kt. The previous forecast had a brief period of gales early Thu in zone anz910. Confidence is just above average with the good agreement, so planning on continuing with the headline for the next forecast. Otherwise will stay with the 12z GFS through the remainder of the short range.
In the medium range, the 12z models all indicate another developing low pres system will move through the area Sat. There had been larger timing and track differences in the 00z runs of the GFS/UKMET/Gem/ECMWF, but the differences have decreased in the 12z cycle. The 00z ECMWF had been about the same timing as the GFS, but was north with the track. The 12z ECMWF trended south, but is now slightly faster. The 00z UKMET had been slower, but trended faster and is now in decent agreement with the 12z ECMWF. The 00z Gem had been slower as well, and continues to remain slower in the 12z run. The GFS has been about the most consistent solution, and takes the low off the nrn mid Atlc coast Sat. It is also the best compromise solution with regards to the speed, and is favored by wpc medium range guidance. As far as the intensity is concerned, the models all show strong development, and all solutions show gales across the nt1 and far srn nt1 waters with this system...mainly in the SW flow over unstable areas ahead of the front. However, the GFS/ECMWF both indicate gales north of the low center. The previous forecast had marginal gales late Fri night with this system. Confidence with the gales is about average, so planning on continuing previous headlines but will extend them into Sat including north of the low center as a result of the agreement on the intensity. Will also limit winds to 35 kt in deference to the weaker 12z UKMET. Otherwise will stay with the 12z GFS 10m winds for the remainder of the medium range period.
.Seas...The 12z wavewatch and ECMWF wam are both initialized well across the offshore waters...except in the Gulf of Maine where both models are a couple of ft low. The models are in decent overall agreement, so will use a 50/50 blend of the two as a compromise solution.
.Extratropical storm surge guidance...N/A.
.Nt1 New England waters... .anz810...south of New England... gale possible Saturday night.
.Nt2 mid-Atlantic waters... .anz915...Hudson Canyon to the great South Channel... gale possible Saturday night. .Anz920...Baltimore Canyon to the great South Channel... gale possible Saturday. .Anz905...The great South Channel to the Hague line... gale possible Thursday. Gale possible Saturday night. .Anz910...East of the great South Channel and south of 39n... gale possible Saturday into Saturday night. .Anz828...Inner waters from Cape Charles Light to Currituck Beach Light... gale possible Friday night. .Anz925...Outer waters from Baltimore Canyon to Hatteras Canyon... gale possible Friday night into Saturday. .Anz830...Inner waters from Currituck Beach Light to Cape Hatteras... gale possible Friday night. .Anz833...Inner waters from Cape Hatteras to Cape Fear... gale possible Friday night. .Anz930...Outer waters from Hatteras Canyon to Cape Fear... gale possible Friday night into Saturday.
.Forecaster Kells. Ocean prediction center.