marine weather discussion for N Atlantic Ocean NWS ocean prediction center Washington DC 954 am EDT sun may 20 2018
.Forecast discussion...Major features/winds/seas/significant .Weather for the North Atlantic ocean W of 50w from 30n to 50n.
The preliminary 12z opc-NCEP surface analysis shows a broad south and southwesterly flow over the waters this morning, with a warm front extending S and se from eastern Nova Scotia, and a pair of cold fronts over western New England and the Great Lakes. The 06z GFS is very similar to the 00z cycle which was used for the ongoing forecast. For the morning update we will only adjust grids slightly in deference to adjacent coastal WFO grids and TAFB grids, and also fit the grids to conditions observed right before issuance time later this morning. The latest GOES visible satellite imagery, and radar and lightning data show scattered showers and a few thunderstorms off the se U.S. Coast with areas of rain over southern New England waters and E of the Delmarva coast. The latest sref thunderstorms guidance shows the highest threat for thunderstorms off the se coast today, and with the cold front crossing the area tonight into Mon. Locally very gusty winds and very rough seas are possible in and near any of the heavier thunderstorms, with winds potentially near gale force or higher in the stronger thunderstorms into Mon.
Seas...sea heights will be adjusted to fit an altimeter pass from earlier this morning which indicated seas up to 9 feet off the mid-Atlantic coast. Otherwise, only minor adjustments will be made for the morning update mainly to align opc sea height forecasts with nearby coastal WFO and TAFB gridded sea heights over the region during the next few days.
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High pressure will remain anchored to the east of the southern waters and that will maintain a weak ridge across the southern waters while weak fronts will pass over the northern waters and pressure gradient will remain fairly relaxed through the forecast period. GOES 16 rgb satellite images still show few cloud clusters over most of the region except north of 40n. Convective clouds are still inland along the coasts from the south eastern states into the Virginia coast. The NCEP map at 06z has a stationary front across the north waters along 40n that extends inland. Area of high pressure with several centers is still east of the region and a ridge extends into most of the central and southern waters which is in line with the latest satellite images. Pressure gradient is fairly relaxed and observed maximum winds are only 25 kt in a few areas.
At 500 mb, an upper level ridge cover the region with a short wave just north of the Great Lakes with some energy that will pass east across the northern waters. Models also show that a few more short waves with some energy will pass through the northern waters during the forecast period. The low lever jet will remain to the north of the region and that will keep most of the shear to the north denying any energy to reach the waters. As such, pressure gradient must remain relaxed across the region keeping winds below gale force threshold.
The global models GFS/ecmwfhr/ukmethr/CMC have initialized fairly well the 06z surface observations. In the short term, the models are in a good agreement on keeping high pressure anchored to the east of the southern waters with a weak ridge across the central and southern waters. In the extended period there is an uncreased chance of energy moving into the northern waters that will start to tighten the pressure gradient over the nt1 waters and the Baltimore Canyon. The global models differ slightly in the extended period on the orientation of a low pressure trough that will be associated with a low that will pass north of the region. Otherwise, the general synoptic pattern will remain the same and so will keep consistency with previous model choice and stay with GFS.
.Seas...They are over 6 ft over the southern waters with a peak at 7 ft while seas are less than 6 ft over the rest of the region with smallest seas at 3 ft over the far north of the Maine waters. Nww3 and ecmwfwave models fit well the 06z observed seas pattern. Both wave models also agree in the short term on slightly building seas over the northern waters to peak at 9 ft. The variations in the wave model solution in the extended period are very dismal and so will keep consistency and stay with a 50/50 blend for the seas.
.Extratropical storm surge guidance...N/A.
.Nt1 New England waters... None.
.Nt2 mid-Atlantic waters... None.
.Forecaster Mills/musonda. Ocean prediction center.