North Atlantic Marine Weather Discussion

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AGNT40 KWNM 260758
MIMATN

Marine Weather Discussion for N Atlantic Ocean
NWS Ocean Prediction Center Washington DC
258 AM EST Wed Feb 26 2020

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

Per IR imagery and GLM data, we've seen a gradual increase in 
convection overnight, primarily along and east of the Gulf Stream
and well advertised in ongoing SREF and NAM guidance. Widespread
thunderstorms remain in the forecast for about the next 36 
hours, and caution continues to mariners for locally very rough 
seas and gusts in excess of gale force in or near any of the 
stronger convection. ASCAT overpasses from late evening provided 
forecast validation with gales south of a low center across 
Baltimore Canyon, centered near 38N69W, which by next forecast 
issuance will have likely moved east of the outer OPC waters. 

Shortwave trough advancing across the central Plains this morning 
will become negative tilted later today into the Ohio Valley, 
digging northeast into a closed upper low across New England 
later Thu into Fri. Northern and southern jet stream interactions
expected to produce a solid 150+ kt jet streak along the eastern
seaboard, promoting surface cyclogenesis from the Mid-Atlantic 
into eastern Quebec along the left exit region of the jet. The 
intensifying low will pull a pair of strong frontal boundaries 
across the OPC waters tonight and Thu. While in large part 00z 
guidance has remained very consistent, there were some notable 
trends that will be accounted for in the next update. Guidance 
unanimously trended stronger with winds ahead of the cold front 
over the southern NT2 waters, and will be expanding headlines 
across Hatteras Canyon in the next forecast issuance. While it is
nearly impossible to pinpoint areas of convection along the 
front or pre-frontal trough, which is likely in part some of the 
cause of the gales, there is enough of a signal to expand these 
headlines with confidence. Across the Gulf of Maine (ANZ800), 
NCEP guidance again held serve with possible storm conditions 
poleward of a strong occluded or warm front lifting across the 
waters Thu, and with the addition of the 00z CMC regional 
guidance, feel comfortable upgrading this to a brief storm 
warning. The UKMET and ECMWF remain noticeably weaker than 
consensus, which is a limiting factor in forecast confidence, but
would rather err on the side of caution. This only represents a 
2-3 kt increase in winds from the 47 kt forecast from previous 
shifts. Thanks to CAR and GYX for the coordination overnight. 

Gales will linger across the northern portions Thu into Fri in
persistent cold air advection, with a series of reinforcing cold
fronts moving offshore. There are then low to moderate chances
for more gale hazards, this time over the southern or central
portions of the Mid-Atlantic offshore waters Sat and Sun as
developing low pressure over the northern NT2 waters pulls
another cold front offshore. Winds are expected to finally
diminish over the waters Sun night as high pressure builds to the
Mid-Atlantic and New England coasts. Overall forecast confidence
through the medium range remains somewhat above average, but too
low to add any gales over the weekend at this time. 

Seas: With leaning NCEP guidance for winds in the near term 
portion of the forecast, will use the WW3 as the basis for the 
significant wave heights through late Thu night. Both sets of 
wave guidance struggle to accurately capture seas across the 
Gulf of Maine in strong easterly flow, such as the case expected 
late Wed night into early Thu. With strong gale and storm 
headlines in the forecast, plan to increase seas as much as 40 
percent above guidance to get forecast values into the 18-22 ft 
range. Otherwise, throughout the vast majority of the medium 
range in persistent W-NW flow, will run a 1:1 blend between the 
WAM and WW3. 

Extratropical Storm Surge Guidance: A brief positive surge, 
around 1 to 2 ft, and slightly higher along the Maine coast, 
still appears possible from Long Island Sound to the Maine coast 
by Wed night into Thu as the increasing easterly winds move 
northward along the coast. For more detailed forecasts and 
information, please see products provided by your local coastal 
National Weather Service forecast offices. 


.WARNINGS...Preliminary.

.NT1 New England Waters...
.ANZ800...Gulf of Maine...
     Gale tonight.
     Storm Thursday.
     Gale Thursday night.
     Gale Possible Friday.
.ANZ805...Georges Bank west of 68W...
     Gale Thursday into Thursday night. 
     Gale Possible Friday.
.ANZ900...Georges Bank east of 68W...
     Gale Thursday into Thursday night. 
     Gale Possible Friday.
.ANZ810...South of New England...
     Gale Thursday into Thursday night. 
     Gale Possible Friday.
.ANZ815...South of Long Island...
     Gale Thursday into Thursday night. 
     Gale Possible Friday.

.NT2 Mid-Atlantic Waters...
.ANZ820...Hudson Canyon to Baltimore Canyon...
     Gale tonight into Thursday night. 
.ANZ915...Hudson Canyon to the Great South Channel...
     Gale Thursday into Thursday night. 
     Gale Possible Friday.
.ANZ920...Baltimore Canyon to the Great South Channel...
     Gale Thursday into Thursday night. 
     Gale Possible Friday.
.ANZ905...The Great South Channel to the Hague Line...
     Gale Thursday into Thursday night. 
     Gale Possible Friday.
.ANZ910...East of the Great South Channel and south of 39N...
     Gale Thursday into Thursday night. 
     Gale Possible Friday.
.ANZ825...Inner Waters from Baltimore Canyon to Cape Charles Light...
     Gale tonight into Thursday night. 
.ANZ828...Inner Waters from Cape Charles Light to Currituck Beach Light...
     Gale tonight.
.ANZ925...Outer Waters from Baltimore Canyon to Hatteras Canyon...
     Gale tonight into Thursday night. 
.ANZ830...Inner Waters from Currituck Beach Light to Cape Hatteras...
     Gale tonight.
.ANZ833...Inner Waters from Cape Hatteras to Cape Fear...
     Gale tonight.
.ANZ930...Outer Waters from Hatteras Canyon to Cape Fear...
     Gale tonight.
.ANZ835...Inner Waters from Cape Fear to 31N...
     Gale tonight.
.ANZ935...Outer Waters from Cape Fear to 31N...
     Gale tonight.

$$

.Forecaster Collins. Ocean Prediction Center.