.Marine weather discussion for N Atlantic Ocean .NWS ocean prediction center Washington DC 330 PM EDT sun 17 Jun 2018
.Forecast discussion...Major features/winds/seas/significant .Weather for the North Atlantic ocean W of 50w from 30n to 50n.
This mornings ascat overpasses covered the offshore waters east of about 74w and indicated winds were 10 kt or less, except across the eastern Gulf of Maine where the southeast winds were up to 15 to 20 kt. The 12z models were well initialized with these generally light winds, and are in above average agreement across the west Atlantic for the next few days. Over the near term, the models are consistent in moving a low pressure trough or weak frontal boundary off the North Carolina coast, which the NAM nest/nmm/arw/hrrr all indicate should enhance the south to southwest winds to 20 kt or so across the waters off Cape Hatteras tonight. Incorporated the 12z NAM nest and 12z nmm into the existing grids through 18z Monday to reflect these details in the forecast winds.
An upper level trough is expected to approach Quebec and northern New England Mon into Tue, and support a relatively strong cold front that will move off the New England coast early Tue. The 12z models remain in well above average agreement with the timing of this front and are also consistent in indicating that the increasing southwest return flow will reach 30 kt across the Gulf of Maine and far northern reaches of Georges Bank Mon evening. Despite the strong low level jet depicted in regional and global guidance - generally 45 to 55 kt - poor mixing over the cooler waters will likely inhibit any gales from making it to the surface. In fact, the 12z NAM nest soundings maintain the strong inversion with the gales limited to about 50m above the surface. We would not be surprised to see some gale force gusts at the elevated stations along the Maine coast, but such observations are unlikely to represent the surface winds. We used a blend of the 12z NAM nest and 12z nmm for the wind grids Mon evening through Tue evening.
The cold front should stall near Currituck Beach Light Wed, then the models diverge somewhat with a developing surface low along the front Wed night/Thu. As has been the case for the last several cycles, the GFS continues to move the front further south than the ECMWF/UKMET Thu, and is further south than the latter models with the low. We will be maintaining forecast continuity and using a blend of the 00z/12z ECMWF for the wind grids Thu through the remainder of the period. The 12z ECMWF appears more reasonable with the stronger east to northeast winds developing poleward of the front across the mid Atlantic waters Thu night into Fri night.
Seas: both the multi-1 ww3 and ECMWF wam appear well initialized with wave heights across the offshore and coastal waters this afternoon. Will use a blend of this guidance in the short term, then generally follow same line of thinking as the wind grids; will use the wam beginning late Mon night. Highest seas to about 11 ft expected Mon night in 30 kt winds across the Gulf of Maine.
Extratropical storm surge guidance: no significant positive surge events are expected during the next several days.
.Nt1 New England waters... None.
.Nt2 mid-Atlantic waters... None.
.Forecaster Clark. Ocean prediction center.