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000
AGNT40 KWNM 201949
MIMATN

Marine Weather Discussion for N Atlantic Ocean
NWS Ocean Prediction Center Washington DC
349 PM EDT Fri Apr 20 2018

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

Note: AWIPS data will not be available at opc until 17z on Apr
21, due to planned maintenance.

Current Conditions...The 12z ncep surface analysis shows a 998
mb low centered just E of Nova Scotia, with an associated cold
front extending SW from the low and skirting the far SE part of
the nt2 area and into the Cape Canaveral region. The analysis
also shows a low pressure trough extending E to W across southern
Nova Scotia, the Bay of Funday and Maine. Lightning density
product data at 1740z shows a couple of lines of scattered
showers and tstms ahead of the cold front, mainly S of 40N.

Models/Forecast...A series of low pressure troughs will pass SE
over the nt1 area tonight into Sun night. A strong high pressure
ridge will move SE over the offshore waters tonight into Mon,
then shift E Mon night through Tue night. Low pressure will move
E along the Gulf Coast Sun night through Mon night, track NE
along the SE coast Tue and Tue night, then move N along the mid
Atlantic coast Wed and up into southern New England Wed night.
The low will push a strong warm front N and NE across the
offshore waters Tue through Wed night. A strengthening pressure
gradient between the low and the ridge Sun night through Tue
night will result in winds increasing into the 30 to 40 kt range
over the nt2 waters for the Mon through Tue night period. The
medium range models are in good overall agreement across the
offshore waters for tonight into Tue, so the representative 12z
gfs 10m solution will be used for the wind grids into early Mon
followed by the 12z gfs 10m/30m solution with the stability smart
tool for later Mon into Tue night. There are some timing and
trajectory differences with the low for Tue night through Wed
night. The 12z gem/gfs show a coastal track, while the 12z
ecmwf/ukmet have a more offshore track. The 12z gfs/ukmet are
slower, while the 12z ecmwf/gem are faster. In order to resolve
the model uncertainty, will use a 50/50 blend of the 12z
ecmwf/gfs for Wed through the rest of the forecast period.
Confidence in the gale warnings for Mon through Tue is average,
then degrades to below average for Tue night through Wed night as
the medium range models diverge.

Seas...Both the 12z wna wavewatch and 12z ecmwf wam initialized
well versus the latest buoy observations. The models are in good
agreement over the offshore waters during the forecast period,
except the ecmwf wam builds up the seas more in the SW nt2 waters
for Mon into Tue, then again in the northern nt2 waters for Wed
and Wed night. So will use a 50/50 blend of the 12z wavewatch
and ecmwf wam over the entire forecast period to smooth out the
model differences.

Extratropical Storm Surge Guidance...Latest run of estofs and
etss indicates a positive surge in the 1 to 2 ft range along the
SE coast for late Sun into Tue, expanding along the mid Atlantic
coast for late Tue through Wed, then stretching up into the nt1
waters late Wed and Wed night. Estofs and etss look reasonable
with the surge, given the strong E to SE flow forecast for the
offshore waters for Sun night through Wed night.

.WARNINGS...Preliminary.

.NT1 New England Waters...
     None.

.NT2 Mid-Atlantic Waters...
.ANZ920...Baltimore Canyon to the Great South Channel...
     Gale Possible Tuesday night into Wednesday.
.ANZ910...East of the Great South Channel and south of 39N...
     Gale Possible Wednesday into Wednesday night.
.ANZ828...Inner Waters from Cape Charles Light to Currituck Beach Light...
     Gale Possible Tuesday night.
.ANZ925...Outer Waters from Baltimore Canyon to Hatteras Canyon...
     Gale Possible Tuesday night into Wednesday.
.ANZ830...Inner Waters from Currituck Beach Light to Cape Hatteras...
     Gale Possible Tuesday into Tuesday night.
.ANZ833...Inner Waters from Cape Hatteras to Cape Fear...
     Gale Possible Tuesday into Tuesday night.
.ANZ930...Outer Waters from Hatteras Canyon to Cape Fear...
     Gale Possible Tuesday into Tuesday night.
.ANZ835...Inner Waters from Cape Fear to 31N...
     Gale Possible Monday into Tuesday.
.ANZ935...Outer Waters from Cape Fear to 31N...
     Gale Possible Monday night into Tuesday night.

$$

.Forecaster Scovil. Ocean Prediction Center.


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