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000
AGNT40 KWNM 171312
MIMATN

Marine Weather Discussion for N Atlantic Ocean
NWS Ocean Prediction Center Washington DC
912 AM EDT Tue Oct 17 2017

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

The latest NCEP surface analysis shows a cold front across the
srn NT2 offshore waters this morning, and a high pres ridge
extending NE to SW along the New England through Mid Atlc coast.
The ridge is interacting with the frontal boundary, and current
sparse wind observations off the SE coast indicate NE flow up to
25 kt. However, the Ascat overpasses from overnight indicated a
few gales in the NE winds which are counter to the flow of the
Gulf Stream. This resulted in an unstable vertical profile which
allowed stronger winds aloft to mix down. The 06Z GFS indicated
that the front will move off to the E today as the ridge
continues to build over the area. The previous forecast had
gales up into 12Z this morning, but will extend them into 18Z
this afternoon as the models typically drop them too quickly, and
the unstable environment should allow for continued mixing up to
that point. In addition, will boost seas as altimeter passes off
the SE coast from 0700 UTC and 1100 UTC indicate the wave models
are initialized low. Cryosat indicated 15 ft in srn NT2 at 0700
UTC which was at least 3 ft lower than what the guidance was
showing.

Otherwise, the 06Z/00Z GFS model runs are in good overall
agreement with the rest of the 00Z guidance with indicating high
pres dominating the pattern in the short range before a weak cold
front passes through NT1 on Thu night and Fri. The previous
forecast stayed close to the 00Z GFS throughout the majority of
the forecast period, so will not be making any significant
changes in the update package as the 06Z GFS has not changed
much.

-----------------------------------------------------------------
PREVIOUS DISCUSSION...

Current Conditions...The 00z ncep surface analysis shows a
strong cold front extending NE to SW across the nt2 area to the
Georgia coast. The analysis also shows a low pres trough oriented
roughly NE to SW and positioned just E of the nt2 area, with a
high pres ridge building E into the nt1 and NW part of the nt2
waters. Latest available ascat hi-res and ascat passes from a few
hours ago show 20 to 25 kt winds in N flow behind the cold front,
and 20 to 30 kt winds in N flow over the northern and central
nt2 waters behind the cold front with a few gusts to 35 kt off
Cape Hatteras. Buoy observations over the past few hours off the
SE coast in N to NE flow have been gusting to the gale force,
including 41004/41022/41033/41008. Lightning density product
data at 07z indicate a line of scattered showers and tstms with
the cold front extending across Blake Ridge and into the far SW
nt2 waters. Am planning to maintain the gale warnings in the
southern nt2 waters into this morning, per earlier coordination
with WFO Charleston.

Models/Forecast...The 00z medium range models are in good
overall agreement across the offshore waters during the forecast
period. 00z ecmwf/gfs appear to be in the best agreement with a
low which is expected to develop near Bermuda on Thu, then move
off to the NE and strengthen Thu night and Fri. Although the 00z
nam 30m solution will be used into this morning to capture the
gales in the nt2 waters behind the cold front, the 00z gfs looks
representative enough to be used for the wind grids through the
rest of forecast period. Am planning to use the 00z gfs 30m for
the wind grids for today and tonight, then switch to using the
00z gfs 10m for Wed through the rest of the forecast period as
the pattern becomes weaker and high pres ridging becomes more
prevalent.

Seas...The 00z wna wavewatch and 00z ecmwf wam both initialized
well over the offshore waters, but the ecmwf wam is more robust
in the nt2 waters for today and tonight and is thus the preferred
model for the wave height grids over this timeframe. The
wavewatch and ecmwf wam are in good overall agreement in the
offshore waters for Wed through the rest of the forecast period,
so the 00z wavewatch will be used starting on Wed.

.Extratropical Storm Surge Guidance...estofs and etss are both
showing a positive surge in the 1.0 to 1.5 ft range along the
northern Florida/Georgia/South Carolina coast for today into
Thu, which looks reasonable given strong NE flow influencing the
region.

.WARNINGS...Preliminary.

.NT1 New England Waters...
     None.

.NT2 Mid-Atlantic Waters...
.ANZ930...Outer Waters from Hatteras Canyon to Cape Fear...
     Gale today.
.ANZ835...Inner Waters from Cape Fear to 31N...
     Gale today.
.ANZ935...Outer Waters from Cape Fear to 31N...
     Gale today.

$$

.Forecaster Kells/Scovil. Ocean Prediction Center.


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