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AGNT40 KWNM 222008
MIMATN

Marine Weather Discussion for N Atlantic Ocean
NWS Ocean Prediction Center Washington DC
408 PM EDT Tue Oct 22 2019

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

The latest GOES visible satellite imagery shows the low clouds
around a low pressure center just SE of the nrn NT2 offshore
waters this afternoon. Ascat wind retrievals from 14Z earlier
today indicated up to 30 kt to the N of the low center as it
interacted with high pressure N of the region over ern Canada.
However, the Ascat indicated the higher winds just E of the
offshore waters, although there was a small area in the data over
nrn NT2 near the Gulf Stream. Current surface reports show no
more than 20 kt, though there are no obs near where Ascat showed
the higher winds. However, the 12Z GFS/ECMWF/W-ARW all indicate
no more than 25 kt in the offshore waters at 18Z as well, and the
guidance indicates that the winds will remain near that intensity
as the low weakens while moving N into the Gulf of Maine
tonight. However, the models also show a second low pressure
moving in from the W, which is expected to absorb the current
system while strengthening the winds ahead of it the SE flow. The
models are in good agreement on the timing of the synoptic
features in the short term, though there are some differences
between the GFS and ECMWF on the intensity of the winds in the SE
flow ahead of the next low. The GFS/ARW indicate an area of
gales for tonight into Wed ahead of the front, which is about 5
to 10 kt stronger than the ECMWF/UKMET solutions. However, there
is a fair amount of support for higher winds mixing down, as the
models are showing a strong low level jet setting up ahead of the
front with 925 mb winds increasing to about 50 kt. Although the
cooler SSTs in the Gulf of Maine normally suppress mixing, the
vertical shear may be sufficient to mix down higher winds from
aloft. In addition, GFS model soundings do indicate mixed layer
winds reaching gale force for tonight, so confidence with the
previous gale warnings is above average as a result of the
marginal support. As such, am planning on maintaining previous
gale headline in the Gulf of Maine for late tonight into Wed.
Will also be populating with the 12Z W-ARW winds into Thu as the
model is well supported by the rest of the 12Z guidance.

The 12Z models indicate that high pressure will build across the
area late Wed and Thu, and the 12Z ECMWF shows the high
continuing over the W Atlc into Fri. The rest of the 12Z models,
aside from the inconsistent GFS, agree fairly well with the
ECMWF on the overall synoptic pattern through the medium range
with only minor differences over the offshore waters. The GFS
becomes an outlier solution as it develops a coastal low Sat,
which is far different from the rest of the guidance and is now a
day slower than the 06Z run. In contrast, the 12Z ECMWF shows a
cold front moving over the area late Sat with the associated low
center moving into the Gulf of Maine late in the day. This
solution is much closer to the consensus of the 12Z guidance, so
planning on switching to the 12Z ECMWF on Thu and continuing with
it through the remainder of the forecast period. Will also be
maintaining no wind hazard headlines beyond Wed as the bulk of
the 12Z guidance shows no clear signal for anything 34 kt or
above, so confidence is low for gales or higher.

Seas...The 12Z Wavewatch and ECMWF WAM agree well over the short
range, before differences develop into the medium range as the
associated atmospheric models start differing. In order to match
up with the wind grids, am planning on using a 50/50 blend in the
short range before relying more heavily on the ECMWF WAM in the
medium range.

.EXTRATROPICAL STORM SURGE GUIDANCE...No significant positive
surge events are expected over the next few days. For more
information, refer to the latest forecasts from coastal National
Weather Service Forecast offices.

.WARNINGS...Preliminary.

.NT1 New England Waters...
.ANZ800...Gulf of Maine...
Gale Wednesday.

.NT2 Mid-Atlantic Waters...
None.

$$

.Forecaster Kells. Ocean Prediction Center.