Marine Interpretation Message
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188
AGNT40 KWNM 130105
MIMATN

Marine Weather Discussion for N Atlantic Ocean
NWS Ocean Prediction Center Washington DC
905 PM EDT Mon Apr 12 2021

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

The latest model guidance indicates that low pressure just east
of the nt2 waters will move slowly east tonight and Tuesday. Gale
force winds are still expected across the outer nt2 waters by
Tuesday. Another low will then move off the mid Atlantic coast by
Thursday with gale conditions developing across portions of the
nt1 and northern nt2 waters by Thursday night. These conditions
will then continue into Saturday. For wind grids will continue to
use the current grids throughout the forecast period. Current
warnings look reasonable and few changes should be needed on the
next offshore waters forecast.

For wave height grids will also continue to use the current grids
throughout the forecast period.

.EXTRATROPICAL STORM SURGE GUIDANCE...The 18Z ETSS and ESTOFS
show a positive surge of 1 to 2 ft, with the ESTOFS being close
to 2 ft, along the Mid-Atlantic and southern New England coasts
tonight into Tue night. This matches up well with the onshore
flow indicated by the atmospheric models. As such, the surge
models seem reasonable. Please monitor products from coastal
National Weather Service offices for detailed water level
information.

-----------------------------------------------------------------
PREVIOUS DISCUSSION...

The GOES visible satellite imagery shows a complex low pressure
system in the W Atlc this evening with areas of showers near the
boundary in the outer offshore waters. The lightning density
product indicates some tstms embedded in the showers, so locally
gusty winds and higher seas can be expected in the vicinity of
these storms. Current surface reports show winds to 25 kt to the
N and W of the system along the coast, which is in line with the
Ascat wind retrievals from 15Z earlier today which showed around
the same. The 12Z GFS/ECMWF are initialized within 5 kt or so of
the data. The models agree fairly well over the short term, and
indicate that the system will move slowly E of the area over the
next 12 to 24 hours. However, the 12Z guidance does show the
trailing cold front moving S across the offshore zones, which
will usher in cold air advection across the W Atlc. The 12Z
models have indicated winds will increase N of the front, with
the higher conditions developing over the warmer SSTs in NT2 as
the cold advection decreases stability. The previous forecast
had gale headlines in the outer NT2 zones for Tue, and this still
seems reasonable since there has been and continues to be a
modest but persistent signal in the guidance for gales. As
such, confidence remains near average on them, so planning on
continuing the previous gale headlines in the next forecast. The
gales are expected to move E of the offshore waters by early Tue
evening, so planning on dropping the gale headlines by then. As
for the wind grids, am planning on starting out with a blend of
the 12Z GFS and ECMWF with the previous grids since the models
agree fairly well over the short term and are not significantly
different from the previous forecast.

The 12Z models then remain in reasonably good agreement over the
remainder of the forecast period on the synoptic pattern,
although there are some differences on the details between the
global models through the medium range period. The 12Z GFS shows
another low pressure system moving across the offshore waters Thu
into Sat, and there has been a modest signal in the model for
gales developing ahead of the front. The rest of the 12Z models
differ some on the timing and intensity, although the agreement
is fairly good with this system considering the range of the
forecast. The models generally show gales developing ahead of the
front, which support the headlines in the previous forecast. As
such, am planning on continuing with the previous gale headlines
Thu into Sat, which were limited to the outer waters. However,
the models do show gales in the inner zones especially in the
Gulf of Maine, where SSTs are roughly +3 C above the historical
average and will allow for deeper mixing in the lower levels. As
such, confidence is near to just above average with the games
here, so planning on adding headlines for them in the next
forecast. As for the wind grids, am planning on continuing the
previous blend of the 12Z GFS and ECMWF with the previous grids
over the remainder of the forecast period as a compromise
solution to the differences between the models.

.SEAS...The 12Z wave guidance is running a little low in the W
Atlc at 18Z, most noticeably in the Gulf of Maine. As such will
be making adjustments to the wave height grids to account for it.
Otherwise, am planning on using a blend of the 12Z GFS Wave
model with the 12Z ECMWF WAM and the previous wave height grids
over the entire forecast period as to match up with the
compromise solution used with the winds.


.WARNINGS...Preliminary.

.NT1 New England Waters...
.ANZ800...Gulf of Maine...
     Gale Possible Friday into Friday night.
.ANZ805...Georges Bank west of 68W...
     Gale Possible Friday.
.ANZ900...Georges Bank east of 68W...
     Gale Possible Friday.

.NT2 Mid-Atlantic Waters...
.ANZ915...Hudson Canyon to the Great South Channel...
     Gale Possible Thursday into Friday night.
.ANZ920...Baltimore Canyon to the Great South Channel...
     Gale Tuesday.
     Gale Possible Thursday into Thursday night.
     Gale Possible Friday night into Saturday.
.ANZ905...The Great South Channel to the Hague Line...
     Gale Possible Thursday night.
.ANZ910...East of the Great South Channel and south of 39N...
     Gale Possible Friday night into Saturday.
.ANZ925...Outer Waters from Baltimore Canyon to Hatteras Canyon...
     Gale Tuesday.
     Gale Possible Thursday.
.ANZ930...Outer Waters from Hatteras Canyon to Cape Fear...
     Gale Tuesday.
     Gale Possible Thursday.

$$

.Forecaster Nolt/Kells. Ocean Prediction Center.



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