marine weather discussion for N Atlantic Ocean NWS ocean prediction center Washington DC 842 am EDT Mon Apr 24 2017
.Forecast discussion...Major features/winds/seas/significant .Weather for the North Atlantic ocean W of 50w from 30n to 50n.
No major changes to the previous and ongoing opc forecast appears necessary from the morning update. The 06z GFS is very similar to the 00z version which was used for the forecast over the next few days.
Low pressure over southern South Carolina and another low lifting north from the northern Bahamas will combine near the South Carolina coast later today or early tonight, with the low lifting north and northeast thereafter. Widespread gales will accompany this low pressure system as it crosses the region later this morning into Wednesday night. No changes to the previous headlines will be made for the morning update. Rain, showers, and strong thunderstorms will also accompany the low as it crosses the waters during the next few days. Currently, the latest radar, satellite and lightning data indicates showers and locally heavy thunderstorms over most of the southern and central nt2 waters moving off to the north. Wind gusts exceeding gale force and very rough seas can be expected in or near the stronger thunderstorms throughout today, tonight and into the middle of the week. Only minor adjustments to the previous grids and forecast will be made for the morning update.
Seas...again, no major changes appear necessary for the morning update. We will adjust grids and the forecast slightly to fit initial conditions and nearby WFO and TAFB forecasts. Currently, sea heights range from 3 to 5 feet over nt1 offshore waters, or off the New England coast to 5 to 8 feet from around the Delmarva southward.
----------------------------------------------------------------- Previous discussion...
Over the short term, as one would hope as the event draws nearer the new 00z models are now overall in good agreement in regards to both their forecast tracks of a significant surface low tracking NNE near the E coast tonight through Wed and its associated forecast gradients. In response to a closed upper low forecast to move towards the se coast, the 00z models remain consistent in forecasting a surface low to lift N into the far SW nt2 waters and merge with another low near the S Carolina coast by late today with associated ESE gales overspreading the srn nt2 waters. Then tonight into Wed the models agree that the surface low will become vertically stacked with the upper low and track slowly NE to off the mid Atlantic coast with the associated gales spreading NE across the nt2 waters. In regards to the forecast track of this low, would favor the more consistent 00z GFS solution, which is supported best by the 00z UKMET/gefs mean. In regards to the associated forecast gradients, believe the 00z GFS solution looks representative. Therefore, plan on populating our forecast wind grids with our smart tool that will place stronger 00z GFS first sigma level winds in unstable areas and weaker 00z GFS 10m winds in stable areas (which will be primarily from the Gulf Stream nwd) for today through Wed with some additional minor edits in deference to the 00z UKMET/ECMWF. So per these winds do not anticipate making any significant timing and/or areal coverage changes to the previously forecasted high confidence gale warnings.
In the long range, as the 00z models forecast the upper low to weaken, to varying degrees they all forecast the associated surface low to also weaken as it tracks to just S of Long Island Wed night (with its associated winds becoming subgale), then dissipate Thu. Overall, would favor the somewhat faster dissipation forecast by the 00z GFS/ECMWF. Therefore after continuing to populate with 00z GFS first sigma/10m winds Wed night, as a compromise will populate with a 50/50 blend of 00z GFS 10m and 00z ECMWF boundary layer winds on Thu/Thu night. Then late Fri/Fri night, with the 00z gefs mean indicating that the 00z GFS is too progressive, will favor the weaker and less progressive 00z ECMWF solution for a weak cold front to approach the New England coast. So will transition to populating with all 00z ECMWF bl winds on Fri/Fri night.
Seas...overall, the 00z wavewatch has initialized the current seas slightly better than the 00z ECMWF wam. With this in mind, and since the 00z GFS will be favored, will populate our forecast wave grids with the 00z wavewatch iii for today through Wed night. Then since a blended 00z GFS/ECMWF solution will become favored, will transition to populating with a 50/50 blend of the two wave models on Thu/Thu night. Then Fri/Fri night, since the 00z ECMWF will become favored, will populate with all 00z ECMWF wam seas.
.Extratropical storm surge guidance...As the strong Ely gradient is forecast develop N of the low pressure center late today and then shift nwd up the mid Atlantic coast tonight into Tue night, the 00z estofs continues to forecast a more significant surge to develop on the coast than forecast by the 00z etss. Overall, would favor the higher 00z estofs solution.
.Nt1 New England waters... None.
.Nt2 mid-Atlantic waters... .anz920...Baltimore Canyon to the great South Channel... gale Tuesday into Tuesday night. Gale possible Wednesday. .Anz910...East of the great South Channel and south of 39n... gale Tuesday night. Gale possible Wednesday into Wednesday night. .Anz825...Inner waters from Baltimore Canyon to Cape Charles Light... gale Tuesday. .Anz828...Inner waters from Cape Charles Light to Currituck Beach Light... gale tonight into Tuesday. .Anz925...Outer waters from Baltimore Canyon to Hatteras Canyon... gale tonight into Tuesday night. Gale possible Wednesday. .Anz830...Inner waters from Currituck Beach Light to Cape Hatteras... gale tonight into Tuesday. .Anz833...Inner waters from Cape Hatteras to Cape Fear... gale today into Tuesday. .Anz930...Outer waters from Hatteras Canyon to Cape Fear... gale today into Tuesday. .Anz835...Inner waters from Cape Fear to 31n... gale today into tonight. .Anz935...Outer waters from Cape Fear to 31n... gale today into tonight.
.Forecaster Mills/vukits. Ocean prediction center.