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000
AGNT40 KWNM 191247
MIMATN

Marine Weather Discussion for N Atlantic Ocean
NWS Ocean Prediction Center Washington DC
747 AM EST Mon Feb 19 2018

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

Current Conditions...The 06z ncep surface analysis shows a high
pressure ridge over the offshore waters, except for a stationary
front extending E to W across the far southern nt2 waters. The
analysis also shows a hurricane force low centered well E of the
offshore waters near 42N51W. Latest available ascat and ascat
hi-res passes from last night show 20 to 25 kt winds over the
E nt1 and NE nt2 waters, with 15 to 20 kt winds across the
southern nt2 waters. Ascat also indicated a large area of 40 to
50 kt winds in the eastern semicircle of the strong low E of the
offshore waters.

Models/Forecast...Concerning the flow pattern and timing of the
main weather features, the medium range models are in good
overall agreement across the offshore waters through the forecast
period. The ecmwf/gfs have been in the best agreement of the
models into Fri, but with a few intensity differences, thus will
use a 50/50 blend of the 00z ecmwf/gfs for the wind grids over
this timeframe to smooth out the intensity differences. The 00z
ecmwf looks like a good comprimise solution for timing
differences evident among the models for later Fri through the
rest of the forecast period, so the ecmwf will be used
exclusively for the wind grids starting later Fri, except it will
be time shifted six hours slower in deference to the slower 00z
ukmet and wpc medium range forecaster guidance.

Seas...The ecmwf wam and wavewatch are both initialized within a
ft or two of the current observations, and are in good agreement
into early Fri. As a result, will go with a 50/50 blend of the
two models as a compromise for today into early Fri. Then will
use the ecmwf wam with a six hour slower time shift exclusively
for later Fri through the rest of the forecast period, in order
to be consistent with the preferred ecmwf winds.

Extratropical Storm Surge Guidance...N/A.

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

The latest GOES infrared satellite imagery indicates an intense
hurricane force low pressure system well E of the offshore
waters this morning, and cold cumulus extending to the W into
the outer NT2 and far SE NT1 offshore waters in the remaining
cold advection. Ascat wind retrievals from 01Z last night
indicated a few 20 kt barbs in the remaining cold advection, and
current surface observations indicate no more than 15 to 20 kt in
the offshore waters at 0600 UTC with high pres building over the
W Atlc. The 00Z GFS and ECMWF winds are initialized well when
compared with the data, and the models indicate that the winds
will remain light this morning with the high pres over the area.
The 00Z GFS and ECMWF then indicate a weak cold front will
approach the New England coast this afternoon into tonight,
before the weak boundary moves offshore late tonight into Tue.
The GFS is a little stronger than the ECMWF with the SW winds
ahead of the front, and indicates up to 30 kt in the warm
advection over the cold SSTs in the Gulf of Maine. The 00Z ECMWF
only indicates 25 kt, and seems a bit more reasonable when
considering the stable boundary layer over the cold waters in
NT1. As a compromise, am planning on starting out with a 50/50
blend of the GFS and ECMWF, which should act to slightly increase
the areal coverage of 25 kt winds.

The models remain in decent agreement through the short range
into Thu night, and indicate a slightly stronger front will
approach NT1 Wed before moving offshore Wed night. The GFS and
ECMWF remain in decent agreement on the timing of the front,
though the GFS again becomes a bit stronger with the winds ahead
of the front. The models then indicate that the front will
continue SE through the offshore waters before stalling over nrn
NT2 by late Thu as another high builds over New England. The 00Z
ECMWF seems a little too weak with the NE flow behind the front,
while the GFS is a bit stronger. As a compromise, am planning on
continuing previous 50/50 blend through Thu night. The 00Z ECMWF
then indicates another front will pass through the region on Sat,
though is faster than the 00Z GFS. The 00Z UKMET is about 6 hours
slower than the 00Z ECMWF, and is near the timing of the WPC
medium range guidance. As a compromise to the timing differences,
am planning on using the 00Z ECMWF from Fri 12Z onward. However,
will time shift the model 6 hours slower to match up better with
the 00Z UKMET and the WPC medium range guidance.

Seas...The 00Z ECMWF WAM and Wavewatch are initialized within a
ft or two of the current data, and are in good agreement into 12Z
Fri. As a result, planning on starting out with a 50/50 blend of
the two models as a compromise. Will then transition solely to
the 00Z ECMWF WAM after 12Z Fri, but will use the same 6 hour
time shift as used with the 00Z ECMWF winds to slow down the
progression of seas associated with the front on Sat.

Extratropical Storm Surge Guidance...N/A.

.WARNINGS...Preliminary.

.NT1 New England Waters...
     None.

.NT2 Mid-Atlantic Waters...
     None.

$$

.Forecaster Scovil/Kells. Ocean Prediction Center.



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