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000
AGNT40 KWNM 240218
MIMATN

Marine Weather Discussion for N Atlantic Ocean
NWS Ocean Prediction Center Washington DC
918 PM EST MON JAN 23 2017

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

Cyclogenesis continues just off the Delmarva Coast this evening
as energy transfers from inland low to dominant triple point low
center. Real-time mesoscale analysis (RTMA) shows a widespread
area of pressure falls nearing 6 to 7 mb in the past 3 hours
northeast of the low center off the coasts of NJ and Long Island.
Surface high pressure was analyzed to 1028 mb at 0000 UTC over
Eastern Quebec, and the increasing pressure gradient between these
synoptic features continues to generate strong onshore east to
northeast winds ahead of the associated occlusion and warm front.
As the low continues to lift north and northeast over the next
24-48 hours, this update will primarily focus on expected near
term marine hazards.

Models: developing nor`easter initialized well in recent 18Z 1/4
degree GFS and higher resolution 4KM NAM and HRRR guidance, and
see no glaring discrepancies in the next 48 hours comparing the
past few cycles of the deterministic GFS. The previously used 12Z
GFS track and intensity remains in excellent agreement compared
to both 12Z GEFS and EPS means, and OPC grid preference for the
next couple of days remains with the GFS.

Winds: storm warnings remain in effect for a large portion of the
northern NT2 and inner portions of the NT1 waters. Storm warnings
will gradually end south to north as the low gains latitude
overnight and tomorrow, ultimately ending around 21Z across the
far northern Gulf of Maine as the system moves over Nova Scotia.
With sufficient mixing of strong 925 mb low level jet (upwards of
70kt), in this update will increase surface winds to 55 kt for the
next 6-12 hours in inner zones 815 and 820. Otherwise will retain
previous grids, using a local smart tool that replaces boundary
layer winds with first sigma layer winds in unstable conditions.
We still expect gusts to hurricane force.

Seas: at 00Z buoy 44066 already up to 24 feet, which is 6 feet
above 18Z WW3 output, and 3 feet higher than WAM guidance. Intend
on making significant increases to the wave height grids in the
near term / through 21Z Tuesday based on these trends, and will
boost seas across the Gulf of Maine nearly 30-40 percent above WAM
guidance where output tends to drastically underperform in these
strong easterly flow events. Ultimately will increase seas to
about 28 feet, matching well with NWS Boston and Gray coastal
offices.

Extratropical Storm Surge Guidance: overnight tonight ESTOFS
outputs positive surge values 3-4 feet along the coast from near
Wachapreague, VA, northward to near Woods Hole, MA, indicating
most places along the coast stand a good chance at eclipsing
highest astronomical tides which portends coastal and inland
flooding. Poring over station data, most sites along the mid-
Atlantic coast are running upwards of a 1/2 to a foot higher than
expected guidance, which is not too surprising since actual winds
are slightly higher than what is currently in the models. In
summary, feel that ESTOFS has a good handle on location, but
current 3-4 feet positive max values may be too low.


-----------------------------------------------------------------

Previous Discussion...

Over the short term, the 12Z models remain in very good agreement
that the developing triple point surface low now moving NE off
the N Carolina coast will track NNE up the mid Atlantic coast
tonight into early Tue while intensifying into a nor`easter...
continue slowly NE across the NT2 waters later Tue/Tue
night...then move off the NE Wed. In regards to the forecast track
of this low, the 12Z GFS solution looks representative since its
supported best by the 12Z GEFS Mean and 12Z UKMET/ECMWF. In
regards to the associated forecast gradients, would prefer the
slightly stronger 12Z NAM/GFS/GEM solutions. Therefore plan on
populating our forecast wind grids for tonight through Wed night
with our smart tool that will place stronger 12Z GFS first sigma
level winds in unstable and weaker 12Z GFS 10m winds in stable
areas. So since these 12Z GFS winds are very consistent do not
plan on any significant short term timing and/or areal coverage
changes to the previously forecasted gale/storm warnings with this
system.

In the long range, versus its previous respective runs, the 12Z
GFS remains consistent in forecasting a cold front to push SE
across the waters Thu/Thu night, which overall is supported by the
other 12Z global models, with gale force associated winds mainly
near the gulf stream across the NT2 waters. So as a compromise,
would favor a blended 12Z GFS/ECMWF solution for this fropa and
with this in mind will populate our wind grids with a 50/50 blend
of the 12Z GFS 10m/first sigma level winds and 12Z ECMWF boundary
layer (BL) winds on Thu into Fri.

Then by late Fri through Sat night to varying degrees the 12Z
models all forecast a broad upper trough to persist near the E
coast while several embedded short wave troughs rotate through its
base. At the surface, this upper level pattern will play out with
a series of surface troughs passing SE across the waters which
will in turn maintain a moderate strong (generally up to 25-30 kt)
WNW gradient throughout much of the waters. So in an attempt to
smooth out their differences and to develop a compromise, plan on
populating with a 33/33/33 blend of the 12Z GFS first sigma winds
and 12Z UKMET/ECMWF BL winds for late Fri through Sat night.

.Seas...The higher 12Z ECMWF WAM has initialized the current seas
better than the 12Z Wavewatch III and as a result will populate
our forecast wave grids with the 12Z ECMWF WAM for tonight. Then
for a compromise and since a blended 12Z GFS/ECMWF solution will
often be used, will transition to populating with a 50/50 blend of
the 12Z Wavewatch III and 12Z ECMWF for Tue through Sat night.

.Extratropical Storm Surge Guidance...In the strong Ely gradient
forecast to shift Nwd across the Nrn waters tonight Tue, the 12Z
ESTOFS remains consistent in forecasting a slightly more
significant surge (up to 3-4 FT,which at times may be too low) to
spread N up the coast from Delaware to SW New England than
forecast by the 12Z ETSS. Would recommend continuing to favor the
higher 12Z ESTOFS solution.


.WARNINGS...Preliminary.

.NT1 New England Waters...
.ANZ800...Gulf of Maine...
     Gale tonight.
     Storm Tuesday.
     Gale Tuesday night.
.ANZ805...Georges Bank west of 68W...
     Storm tonight.
     Gale Tuesday.
     Gale Possible Thursday night.
.ANZ900...Georges Bank east of 68W...
     Gale tonight into Tuesday.
     Gale Possible Thursday night.
.ANZ810...South of New England...
     Storm tonight.
     Gale Possible Thursday night.
.ANZ815...South of Long Island...
     Storm tonight.
     Gale Tuesday night.
     Gale Possible Thursday night.

.NT2 Mid-Atlantic Waters...
.ANZ820...Hudson Canyon to Baltimore Canyon...
     Storm tonight.
     Gale Tuesday into Tuesday night.
     Gale Possible Thursday night.
.ANZ915...Hudson Canyon to the Great South Channel...
     Gale tonight into Tuesday night.
     Gale Possible Thursday night.
.ANZ920...Baltimore Canyon to the Great South Channel...
     Gale tonight into Wednesday.
     Gale Possible Thursday into Thursday night.
.ANZ905...The Great South Channel to the Hague Line...
     Gale tonight into Tuesday.
     Gale Possible Thursday night.
.ANZ910...East of the Great South Channel and south of 39N...
     Gale tonight into Wednesday.
     Gale Possible Thursday into Thursday night.
.ANZ825...Inner Waters from Baltimore Canyon to Cape Charles Light...
     Gale Tuesday into Tuesday night.
.ANZ828...Inner Waters from Cape Charles Light to Currituck Beach Light...
     Gale Tuesday into Tuesday night.
     Gale Possible Thursday.
.ANZ925...Outer Waters from Baltimore Canyon to Hatteras Canyon...
     Gale tonight into Wednesday.
     Gale Possible Thursday into Thursday night.
.ANZ830...Inner Waters from Currituck Beach Light to Cape Hatteras...
     Gale Tuesday into Tuesday night.
     Gale Possible Thursday.
.ANZ833...Inner Waters from Cape Hatteras to Cape Fear...
     Gale Possible Thursday.
.ANZ930...Outer Waters from Hatteras Canyon to Cape Fear...
     Gale Tuesday into Tuesday night.
     Gale Possible Thursday into Thursday night.
.ANZ835...Inner Waters from Cape Fear to 31N...
     Gale tonight into Tuesday.
     Gale Possible Thursday.
.ANZ935...Outer Waters from Cape Fear to 31N...
     Gale tonight into Tuesday.
     Gale Possible Thursday.

$$

.Forecaster Collins/Vukits. Ocean Prediction Center.


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