North Atlantic Marine Weather Discussion

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AGNT40 KWNM 181328
MIMATN

Marine Weather Discussion for N Atlantic Ocean
NWS Ocean Prediction Center Washington DC
928 AM EDT Mon Jun 18 2018

.FORECAST DISCUSSION...Major features/winds/seas/significant 
.weather for the North Atlantic Ocean W of 50W from 30N to 50N.

Isolated thunderstorm activity was noted via GOES-16 satellite 
imagery this morning over portions of the southern NT2 waters.
The strongest thunderstorms are presently located south of Cape
Lookout and are nearing the southwest portion of ANZ833. Note 
that gusty winds and locally higher seas are possible in and 
near strong thunderstorms. Elsewhere, the 12Z OPC preliminary 
surface analysis depicts 1022 mb high pressure east of the 
offshore waters near 37N66W this morning.

No notable changes to the forecast this morning as the inherited
grids appear reasonable based on current trends. Still expect
strengthening southwest flow over the NT1 waters later today
through tonight ahead of an approaching cold front. Will continue
to carry 30 kt winds tonight with seas building to 11 ft over 
the Gulf of Maine. The stable low-level environment depicted in
model soundings suggests gales remain unlikely overnight.

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PREVIOUS DISCUSSION...

Very tranquil conditions persist across the offshore waters this 
morning. Localized area of winds to around 20 kt noted in ASCAT
overpass between 0130z-0212z currently across southern Baltimore
Canyon associated with a weak surface trough. Otherwise, winds 
are generally 15 kt or less. Overnight regional guidance from the
NAM Nest and NMM initialized these satellite-sensed winds the 
best.

Light winds will continue into the afternoon as surface high near 
37N 67W slowly shifts farther SE of the area, allowing return SW
flow to develop quickly across the offshore waters. An upper 
trough will continue moving E across Quebec and northern New 
England today into Tue, and support a relatively strong cold 
front that will move off the New England coast between 06z-09z 
tonight. Except for the slightly faster 00z GFS, the remainder of
the overnight 00z guidance remains in good agreement with the 
timing of the boundary. 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, echoing previous cycles,
the 00z 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. For near term grids into about 00z 
Wed, plan to use a blended solution between the 00z NAM Nest and 
the 00z NMM, continuing to carry highest winds to 30 kt across 
the Gulf of Maine and the northern portions of Georges Bank. 

The cold front should stall near Currituck Beach Light Wed, with
a weak surface low forming along the front Wed night near the
Delmarva. Low tracks E along the boundary Thu and Thu night, 
pulling the front into the southern waters Fri and Fri night. 
ECMWF has remained the most consistent solution for the past 
couple of days, and with this in mind will run a 1:1 blend of the
12z and current 00z cycle of the ECMWF through the remainder of 
the forecast period. This keeps forecast continuity within OPC 
grids. Worth mentioning the GFS had been largely ignored during 
this time frame with the cold front stalling much farther south 
than any other deterministic model, but both the 18z and now 00z 
runs have trended farther north and are much closer to the 
ongoing ECMWF solutions.

Seas: 00z ECMWF WAM initialized seas better on the 06z sea state
analysis, in particular for a higher area of 3-4 ft seas along
the Gulf Stream adjacent to the NC and SC coasts. With this in
mind, and since the GFS trended too fast with the strong cold
front tonight, will load near term grids through 00z Tue with 
the 00z WAM. Will then generally follow the same line of thinking
as the wind grids; will use a 1:1 blend between the 12z/00z WAM 
for the remainder of the forecast. Highest seas to 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. 



.WARNINGS...Preliminary.

.NT1 New England Waters...
     None.

.NT2 Mid-Atlantic Waters...
     None.

$$

.Forecaster Reinhart/Collins. Ocean Prediction Center.