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AGNT40 KWNM 181242

Marine Weather Discussion for N Atlantic Ocean
NWS Ocean Prediction Center Washington DC
742 AM EST Sun Feb 18 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 1007
mb low centered about 195 nm E of Cape May, which is expected to
move E and rapidly intensify. A cold front extends SW from the
low into the Cape Hatteras region, with a warm front extending E
from the low and across the NE nt2 waters. Latest available ascat
and ascat hi-res passes from last night show 25 to 30 kt winds
over the northern nt2 waters, with 20 to 25 kt winds over the
southern nt1 waters. Lightning density product data at 1220z
shows scattered showers and tstms over zone 910 in the NE nt2

Models/Forecast...The medium range models are in good overall
agreement across the offshore waters during the forecast period
regarding the flow pattern and timing of the main weather
features. The 00z ecmwf appears to have the best handle on the
conditions associated with the rapidly intensifying low tracking
NE across the northern nt2 waters this morning, based on strong
upper level support evident with this low, and the 00z ecmwf
supports hurricane force winds for this morning in zone 905 in
the far NE part of the nt2 area. The ecmwf/gfs have been in the
best agreement through the forecast period but with a few
intensity differences, so will use a 50/50 blend of the 00z
ecmwf/gfs for the wind grids for this evening through the rest of
the forecast period. Confidence is above average for a hurricane
force wind warning E of the offshore waters this afternoon.

Seas...Will adjust the previous wave height grids for today
upwards in order to match the trend with the ecmwf winds. A
50/50 blend of the 00Z ecmwf wam/wavewatch will be used this
evening through the rest of the forecast period, in order to
match up with a 50/50 blend of the ecmwf/gfs being used for the
wind grids.

Extratropical Storm Surge Guidance...N/A.


The latest NCEP surface analysis indicates low pres off the mid
Atlc coast over the nrn NT2 offshore waters, and current surface
reports indicate up to 30 kt across the W Atlc. Ascat wind
retrievals from 01Z last night indicated up to 30 kt near the low
pres system, with the highest winds over NT2 in the southerly
flow ahead of the associated front over the Gulf Stream. The 00Z
GFS/ECMWF/UKMET/NAM winds are all initialized low when compared
with the Ascat, though all of the models indicate that the low
will rapidly intensify over the next 12 to 24 hours as it moves
through the nrn NT2 waters. The models have been consistently
indicating winds will increase to storm force over the Gulf
Stream by early today in NE NT2, though the new ECMWF indicates a
small area of hurricane force winds by 15Z today in the strong
cold advection just W of the low center over far NE NT2. The
guidance has been trending stronger with this system, and a GFS
model cross-section indicates a strong stratospheric intrusion
will develop to the S of the low center later today. This is
indicative of stronger winds aloft mixing down, and the models
all indicate a very strong shortwave trough associated with this
developing system that will start tilting negatively early this
morning. Couple all this with the low wind bias the models have
had this winter, and the result is above average confidence with
a brief period of hurricane force winds in the eastern offshore
waters for a brief period today. As a result, planning on staring
out with the previous wind grids, but will incorporate the 00Z
ECMWF for today and start a hurricane force wind warning for 15Z
today. The models then all indicate the system will become even
more intense to the E of the offshore waters today into Mon, with
winds 75 kt or higher in the GFS and ECMWF solutions. Confidence
is well above average for the hurricane force warning E of the
area as the models have been consistent on this scenario, and are
all above the minimum threshold of 64 kt.

Otherwise, the 00Z GFS and ECMWF agree somewhat well through the
forecast period on the synoptic pattern, and all indicate high
pres will briefly build over the area later today into Mon. The
models then indicate that a front will slowly approach the
offshore waters Tue and Wed before moving offshore Thu. There had
been timing differences in previous runs of the GFS and ECMWF,
but the 00Z models are in decent agreement on the timing.
However, the GFS remains a bit stronger with the winds ahead of
the front over the colder waters in the Gulf of Maine, and seems
a little overdone for warm advection over a stable environment.
ON Thu however, the 00Z ECMWF seems a little weak with the NE
flow behind the front as is moves S through the area. As a
result, planning on using a 50/50 blend of the 00Z GFS and ECMWF
through the majority of the forecast period as a compromise to
the intensity differences between the two solutions.

Seas...Planning on adjusting previous wave height grids for today
to match the upward trend in the ECMWF model winds. Will then use
a 50/50 blend of the 00Z Wavewatch and ECMWF WAM from tonight
through the remainder of the forecast period to account for the
minor differences between the two solutions which are in good
overall agreement.

Extratropical Storm Surge Guidance...N/A.


.NT1 New England Waters...
.ANZ800...Gulf of Maine...
     Gale today.
.ANZ805...Georges Bank west of 68W...
     Gale today.
.ANZ900...Georges Bank east of 68W...
     Storm today.

.NT2 Mid-Atlantic Waters...
.ANZ915...Hudson Canyon to the Great South Channel...
     Gale today.
.ANZ920...Baltimore Canyon to the Great South Channel...
     Gale today.
.ANZ905...The Great South Channel to the Hague Line...
     Hurricane Force today.
.ANZ910...East of the Great South Channel and south of 39N...
     Gale today.
     Storm today.


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