North Atlantic Marine Weather Discussion

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AGNT40 KWNM 270715

Marine Weather Discussion for N Atlantic Ocean
NWS Ocean Prediction Center Washington DC
315 AM EDT Fri Apr 27 2018

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

Over the short term, little change will be made to the ongoing
OPC forecast, and we will populate the grids with a 50/50 blend 
of the old grids and with the 00Z GFS first sigma layer winds
for today into Sat, with any gales occurring either E of the
waters later Sat, where the pressure gradient will be the 
strongest, or in and near any scattered to numerous thunder- 
storms that move over especially NT2 waters early today, then
over most of the region later today, tonight into Sat. The
latest GOES16 IR satellite imagery, radar, and lightning 
products show scattered thunderstorms from E and S of Cape Fear
northward to just E and NE of Cape Hatteras early this morning, 
with additional activity further inland from Maryland southward 
to South Carolina. We will attempt to highlight winds to gale 
force in those zones most likely impacted by the stronger
thunderstorms today, which appears to be from near the Delmarva
southward to S of Cape Fear. Caution is advised for very gusty
winds, and very rough seas in and near any of the stronger 
thunderstorms that cross the waters today into Sat. Low pressure
over far southern Virginia early this morning is still forecast
to track NE, and reach a position near Long Island later today,
and then continue NE along the New England coast tonight,
reaching Maine and SE Canada Sat. A warm front extending E from
the low will lift N over the waters today, followed by a weak
trailing cold front extending S and SW from the low. Confidence
levels remain above average over the region during the short
term, with very good model agreement noted.

Over the medium range, we will trend the forecast and grids more
toward the 00Z ECMWF guidance as it appears to be a good median
solution, and has remained the most consistent over the past few
days. For now, we will not boost the ECMWF winds, as it now
brings stronger winds mainly E of the waters Sat night and again
Mon night into Tue, with marginal gales E of the offshore waters
at those times, which it did not indicate in previous cycles. If
the trend continues we may need to add some gales to the outer
NT2 waters Sat night, and possibly again Mon night into Tue. For
now, we feel that it is best to cap maximum winds at 30 kt over
the waters, and continue to monitor future model guidance. 
Overall, the main weather features will be a series of cold
fronts or low pressure troughs passing E and SE over the New 
England and mid-Atlantic waters Sat night into Tue night, while
a large high pressure area builds SE from the midwest toward the
SE states late Sun and Sun night, and then slowly moves E over
the southern portions of the NT2 waters Mon into Tue night. Most
of the 00Z guidance now indicate stronger lows forming on one of
the fronts E of the northern NT2 and NT1 waters Sat night into
Sun, and again form another low in this same general area late
Mon night into Tue. Again, should this trend continue gales may
need to be added to the outer offshore waters well off the New
England and potentially mid-Atlantic coast Sat night, and
possible again Mon night or Tue. Please closely monitor the 
latest OPC forecast. Confidence over the medium range portion
of the forecast is near average.

Seas...Sea heights range from 10-11 feet over the outer New
England and NE NT2 waters, to around 4-5 feet closer to the 
coastal waters off the mid-Atlantic and SE coast early this 
morning, with seas heights already re-building to 7-8 feet off 
the South and North Carolina coasts early this morning, per the 
06Z OPC RA1 sea state analysis. It appears as if the 00Z ECMWF
WAM guidance has initialized the best early this morning over 
the region based on the latest observations and altimeter data. 
For the early morning package we will remain close to the WAM 
guidance with a few manual edits in deference to nearby coastal 
WFO and TAFB grids through the weekend into early next week.

.EXTRATROPICAL STORM SURGE GUIDANCE...No major deviation from the
latest ESTOFS guidance appears needed through the weekend into
early next week, with no significant surge events anticipated.


.NT1 New England Waters...

.NT2 Mid-Atlantic Waters...


.Forecaster Mills. Ocean Prediction Center.