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000
AGNT40 KWNM 260151
MIMATN

.Marine Weather Discussion for N Atlantic Ocean
.NWS Ocean Prediction Center Washington DC
945 PM EDT SAT 25 MAR 2017

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

At 00Z, the stationary front extended off the mid Atlantic coast
north of Cape May. Buoy 44066 north of the front reported 19 G
23 kt last hour. The latest models are consistent in showing
these easterly winds north of the front will increase tonight,
to 25 kt or so. In the medium range, todays models have not come
into any better agreement with the series of upper shortwaves
and eventual closed low moving through the norhteastern US and
New England waters Tuesday night into Thursday. The 18Z GFS even
trended slightly stronger with the upper low and associated
surface low across the New England waters at that time. Needless
to say, forecast confidence remains well below average beyond
day3. Wave heights across the southern New England and northern
mid Atlantic offshore waters are currently about 1 to 2 ft
higher than the 18Z Wavewatch III and 12Z ECMWF WAM. Buoy 44066
off the New Jersey coast reported 6 ft at 00Z. Will make some
minor near term adjustments to the wave height grids, but
otherwise they look reasonable.

----------------------------------------------------------------
...Previous Discussion...

Over the short term, the new 12Z models present no major
forecast problems. Overall, the models share similar timing for
weak cold front to drift S across the Nrn NT2 waters tonight,
stall Sun, then slowly lift back NEwd across the Nrn waters as a
warm front late Sun night into Mon night, with a weak frontal
wave tracking NE across the NT1 waters Mon night. With the
support of the 12Z GEFS Mean, would favor the slightly less
progressive 12Z GFS/ECMWF solution for this fropa vs the
somewhat faster 12Z UKMET/GEM. Therefore, plan on populating our
forecast wind grids for tonight through Tue with the 12Z GFS
solution by using our smart tool that will place stronger GFS
first sigma level winds in unstable areas and weaker 12Z GFS 10m
winds in stable areas.

In the long range, the disparity between the 12Z global models
increases significantly. Versus its previous respective runs, in
response to a digging upper level trof that is forecast to
transition into a closed upper low and pass across the Nrn
waters, the 12Z GFS remains consistent in forecasting an
associated developing surface low to move to the Nrn Mid
Atlantic coast late Tue, track NE across the NT1 waters Tue
night, then intensify NE of the waters Wed into Thu as it
becomes nearly vertically stacked with the closed upper low.
Overall, the 12Z GEFS Mean supports this 12Z GFS solution. The
12Z UKMET/ECMWF only in general support the 12Z GFS, but are
both more progressive and weaker. The 12Z GEM solution looks
like a complete outlier in the long range and will be
disregarded. Believe the 12Z GFS solution is likely too
amplified while the 12Z UKMET/ECMWF are not amplified enough.
Therefore, with not a particularly high level of forecast
confidence, will attempt to develop a compromise solution by
populating with a 50/50 blend of the 12Z GFS first sigma/10m
(time shifted 3 hours slower Tue night through Wed night) and
12Z ECMWF boundary layer winds for Tue night through Thu night.

.Seas...Overall, the 12Z Wavewatch III has initialized the
current seas slightly better than the 12Z ECMWF WAM. With this
in mind and since the 12Z GFS solution will be favored, will
populate our forecast wave grids with the 12Z Wavewatch III for
tonight through Tue. Also of note then, in association with a
gale center expected to pass S then SE of Bermuda, the 12Z
Wavewatch III remains consistent in forecasting long period
associated SE swell to overspread the waters from S to N Mon
night into Tue night, which will enhance the significant seas.
Then as a compromise, for Tue night through Thu night will
transition to populating with a 50/50 blend of the two wave
models, with the same 3 hour time shift with the Wavewatch III.
Will also then boost this blend up 10 percent on average late
Wed through Thu as the somewhat higher 12Z Wavewatch III seas
are preferred in the cold air advection in the Nly gradient.

.Extratropical Storm Surge Guidance...N/A.

.WARNINGS...Preliminary.

.NT1 New England Waters...
     None.

.NT2 Mid-Atlantic Waters...
     None.

$$

.Forecaster Clark/Vukits. Ocean Prediction Center.



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