.Marine weather discussion for N Atlantic Ocean .NWS ocean prediction center Washington DC 255 PM EST Tue 21 Nov 2017
.Forecast discussion...Major features/winds/seas/significant .Weather for the North Atlantic ocean W of 50w from 30n to 50n.
This mornings 1415z and 1500z ascat overpasses returned southwest winds to 25 kt extending offshore from near Cape May northeast to Martha's Vineyard as well as across the Gulf of Maine. The 12z models were generally well initialized with these winds, and are in good agreement that these winds will expand eastward across the nt1 and northern nt2 zones tonight as a cold front slowly approaches the coast through early Wed. The 12z GFS and 12z ECMWF then remained stronger than the 12z UKMET/NAM/CMC with the developing surface low expected to track northeast across the outer nt2 zones tonight through Wed evening. Versus its previous run, the 12z GFS trended slightly faster with this feature, but also was further northwest with the track of the low and now is very close to the 12z ECMWF which has shown remarkable run to run consistency with the low. The 12z GFS is also faster than the 12z ECMWF in developing the associated gale and storm force winds. The 12z UKMET as well as the 12z gefs support the slower timing. Will update the wind grids with the 12z ECMWF through Wed night and plan to maintain continuity with the wind hazards, limiting them to the outer nt2 zones as well as anz900 Georges Bank. We have well above average forecast confidence that warnings will be limited to the outer zones, well east from any mid Atlantic coastal zones. The 12z GFS/ECMWF then both show a weaker low will move northeast across the nt2 waters south of Cape Fear late Thu into Fri, with the 12z GFS slightly faster than the 12z ECMWF. Per the ECMWF/UKMET will limit the winds associated with this feature to 25 kt.
The GFS then lacks any run to run consistency with the next developing low forecast to move northeast across the outer nt2 waters Fri night through Sat night, and continued to flip flop between producing gale force winds across these zones. The 12z GFS was again stronger, similar to the 00z run. The ECMWF has been consistently weaker and is supported by the 12z UKMET. Given the difference in the models we are reluctant to go with any winds higher than 30 kt, and will populate the wind grids with the 12z ECMWF through Sat night. The 12z ECMWF is much more amplified than the remaining guidance with the sharp upper level trough moving through New England sun and passing offshore Sun night. At the surface, and to varying degrees, the models all indicate strong northwest winds will develop behind the cold front, with the stronger ECMWF even showing some gales across the nt1 and northern nt2 waters. To tone down these winds and account for some of the forecast uncertainty will use an even blend of the past two runs of the ECMWF for the wind grids which will limit winds to 25 or 30 kt sun/Sun night.
.Seas...Gulf of Maine buoy 44037 and buoy 44025 south of Long Island both reported 8 ft at 18z, which is about 1 ft higher than the 12z wavewatch iii and 12z ECMWF wam. The 12z ECMWF wam then appears slightly too high with the wave heights associated with the developing storm Wed/Wed night. So will use a 75/25 12z ECMWF wam/12z ww3 blend to tone down these seas slightly Wed/Wed night. Thereafter am favoring an even blend of the above guidance.
.Extratropical storm surge guidance...N/A.
.Nt1 New England waters... .anz900...Georges Bank east of 68w... gale Wednesday night.
.Nt2 mid-Atlantic waters... .anz915...Hudson Canyon to the great South Channel... gale Wednesday. .Anz920...Baltimore Canyon to the great South Channel... gale Wednesday. .Anz905...The great South Channel to the Hague line... gale Wednesday. Storm Wednesday night. .Anz910...East of the great South Channel and south of 39n... storm Wednesday. Gale Wednesday night. .Anz925...Outer waters from Baltimore Canyon to Hatteras Canyon... gale Wednesday. .Anz930...Outer waters from Hatteras Canyon to Cape Fear... gale tonight into Wednesday. .Anz935...Outer waters from Cape Fear to 31n... gale tonight.
.Forecaster Clark. Ocean prediction center.