Hurricane Force Warnings in Effect
Atlantic:  High Seas

North Atlantic Marine Weather Discussion

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AGNT40 KWNM 232011
MIMATN

Marine Weather Discussion for N Atlantic Ocean
NWS Ocean Prediction Center Washington DC
311 PM EST Sat Jan 23 2021

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

A potentially powerful low pressure system could impact the 
offshore waters by Wed night through Thu night. Gale to storm 
force winds now appear more likely with this system Wed through 
Thu night, with hurricane force winds possible, especially near
the Gulf Stream. All marine interests should closely monitor the
latest OPC and coastal forecasts in the coming days, and begin 
to develop avoidance plans.

ASCAT data from this morning indicated a wide swath of 30 kt 
west to northwesterly winds from the New England and northern 
Mid-Atlantic coast east and southeastward over the offshore 
waters. Over the short term, tonight into Mon night, the 12Z 
model guidance is in very good agreement over the offshore 
waters. For this time period, we will rely on a 90 percent 
previous OPC grids, 10 percent 12Z GFS first sigma layer wind 
blend for our refreshed gridded forecast this afternoon. This 
will result in no change to the previous hazards with widespread 
gales likely from the outer central NT2 waters northeastward and 
northward across the northern NT2 and NT1 waters tonight into 
Sun, with gales ending from W to E Sun night over the offshore 
waters as the pressure gradient strong high pressure building E 
toward the eastern states and developing low pressure E of the 
waters weakens. A weakening high pressure ridge will cross the 
region Mon with the next low pressure system and associated 
fronts impacting the waters near and off the Carolina and 
Delmarva coasts Mon night and early Tue. SW gales associated 
with this system still appear likely off the Carolina coast Mon 
night. Forecast confidence is above average tonight into early 
Tue.

Over the medium range, all eyes will begin to focus on a 
potentially significant low pressure system that should impact 
at least parts of the offshore waters Wed night through later 
parts of next week. It does appear that the 12Z model guidance 
has come into a little better agreement verses the 00Z guidance 
from last night, with the GFS and ECMWF trending towards a more 
common solution. As we have been following the more conservative 
ECMWF solution over the past few days, we will again trend the 
OPC gridded forecast closer to the 12Z ECMWF for the afternoon 
package, and use the bias-corrected version of the winds over 
the medium range. Therefore, for now we will go ahead and add 
storm force winds possible mainly near the north wall of the Gulf
Stream by Thu afternoon and night, with conditions then slowly 
improving as the potentially powerful low pressure system moves 
off to the E of the waters later in the upcoming week. Also, 
until better model agreement develops in the coming days, we will
cap winds at 55 kt near the north wall, and make adjustments to 
the forecast in the coming days once even better model agreement 
develops. Both the 12Z ECMWF and 12Z GFS are beginning to show 
the potential for hurricane force winds developing with this 
strong low pressure system by Thu into Fri, and all mariners are 
stronger urged to closely monitor the latest OPC forecast and 
begin to examine avoidance plans over the region for middle to 
later parts of the upcoming week. Forecast confidence overall is 
near average for the afternoon package during the medium range.

.Seas...To best match the wind forecast, we will use a 90 percent
previous grids, 10 percent 12Z Wavewatch blend for tonigh into
early Tue, and then transition grids closer to the 12Z ECMWF WAM
guidance to best match the wind forecast. We will add up to 10 to
15 percent to the grids in and near the gale force wind areas
Tue, then again on Thu. For now, as we are capping winds at 50-55
kt mainly near the north wall of the Gulf Stream by Thu night, 
we will cap waves at 30 ft or so. Again, additional adjustments
are likely over the next few days and all mariners should use
caution and closely monitor the latest forecast.

.EXTRATROPICAL STORM SURGE GUIDANCE...No significant positive surge
is expected for the next few days. A modest positive surge event
could develop by Tue into Wed as onshore winds develop N of a
front and low pressure tracking E and SE along the front mainly
from the northern North Carolina coast northward to the coast of
New Jersey. A potentially more significant positive surge event 
is possible along portions of the Mid-Atlantic and New England 
coast by Thu as a possibly quite significant low pressure system
impacts the region. The exact surge and where the highest surge
will develop has yet to be determined as some variability in the
exact track and intensity of the low still exists. Please monitor
the latest forecast and as always, keep abreast of the latest 
information from local National Weather Service offices.

.WARNINGS...Preliminary.

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

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

$$

.Forecaster Mills. Ocean Prediction Center.