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000
AGNT40 KWNM 180156
MIMATN

.Marine Weather Discussion for N Atlantic Ocean
.NWS Ocean Prediction Center Washington DC
855 PM EST TUE 17 JAN 2017

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

As was noted below, the latest models are in very good agreement
across the west Atlantic for the next few days. Forecast
confidence remains well above average with the gales to develop
Wednesday and Wednesday night as the upper level low currently
near northern Illinois moves toward the mid Atlantic coast and
across the NT2 waters tonight through Wednesday night. Versus
its previous run the 18Z GFS trended slightly stronger with
these gales. With this evenings forecast updates did expand the
gale warning to the outer waters south of Cape Fear. Otherwise
we did not make any significant changes to the previous offshore
forecasts. The 12Z ECMWF WAM is well initialized with wave
heights across the west Atlantic this evening. Although the wave
heights are currently 4 ft or less across the NT1 and NT2 waters
this evening, the 18Z Wavewatch 3 is about 1 ft low north of
Cape Cod Bay, across the Gulf of Maine and, also southeast of
Cape Charles.

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

Overall, the 12Z global models and NAM are in good agreement
over the waters for the next 3 to 5 days. The main weather
features impacting the waters will be intensifying low pressure
forming as a secondary or triple point low early Wednesday,
while the primary low center dissipates over northeast New York
state. This low then tracks east and southeast from the southern
NT1 waters Wednesday into Thursday while intensifying east of
the offshore waters. A second event at the end of Day 5 or
Sunday night as an upper low crossing the southern Plains and
interior southern states spawns a stronger developing low
approaching the mid Atlantic coast.

Before the first event high pressure currently over the southern
waters and high pressure ridging down into the NT1 waters will
recede southeast and northeast respectively into tonight as a
weak cold front in the southern NT1 waters stalls and then
begins to push northeast later tonight as low pressure forms
near Long Island. The low will move east and southeast from near
Long Island by 12Z Wednesday to east of the northern NT2 waters,
near 37N 64W, by 06Z Thursday. Fairly widespread gales appear
likely over portions of the NT2 waters into the far southeastern
NT1 waters Wednesday into Thursday. High pressure will follow
the low, and push east over the region later Thursday into
Friday. For Friday night into Saturday night another low is
expected to pass east across the central and southern NT2
waters, with high pressure building south and southeast over the
waters in the wake of the low later Saturday and Saturday night.
At this time, gale force winds appear unlikely with the late
week low pressure system. For the new forecast, tonight we will
rely on the 12Z GFS 10 meter winds over the offshore waters, and
then later tonight through Saturday night when model agreement
is best, will use the 12Z GFS using a smart tool which places
the stronger first sigma layer winds over unstable areas, and
slightly lower 10 meter winds over stable areas. Then for Sunday
and Sunday night or Day 5 we will use an even blend of the 12Z
GFS and 12Z ECMWF over the region to account for minor
differences in the guidance. Confidence levels in the forecast
are near to above average over the next several days.

.Seas...The 12Z Wave Watch III has initialized a bit too low
over the outer NT1 and northeast NT2 waters where 5 to 6 foot
sea heights have been detected by buoy and altimeter data.
Elsewhere 12Z Wave Watch III and ECMWF WAM have initialized
quite well. There is concern in forecast thet Wave Watch III may
not build the seas enough or fast enough for the areas from the
central and northern NT2 waters and over the NT1 waters
especially associated with the developing low later tonight into
Wednesday night. For the new package we will use the 12Z ECMWF
WAM with its somewhat higher values tonight into Wednesday
night. After 06Z Thursday we will use a 50-50 blend of the
Wavewatch and WAM models, as both models are otherwise in pretty
good agreement over the region out to Sunday night.

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

.WARNINGS...Preliminary.

.NT1 New England Waters...
.ANZ805...Georges Bank west of 68W...
     Gale Wednesday into Wednesday night.
.ANZ900...Georges Bank east of 68W...
     Gale Wednesday into Wednesday night.

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

$$

.Forecaster Clark/Bancroft. Ocean Prediction Center.


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