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AGNT40 KWNM 221415
MIMATN

.Marine Weather Discussion for N Atlantic Ocean
.NWS Ocean Prediction Center Washington DC
915 AM EST THU 22 FEB 2018

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

The winds at NOAA buoy 44066, 75 nm east of the New Jersey coast
and just poleward of the stationary front, increased to 25 kt
last hour. The latest guidance is consistent that these easterly
winds will further increase this evening into tonight. The 06Z
GFS even is showing some winds approaching gale across ANZ820
around 00Z. Blended in some of the higher 00Z HiResW ARW into
the previous OPC wind grids to reflect this. There are some
timing differences between the global models with the cold front
Sun night into Mon night. But otherwise, models are in above
average agreement across the west Atlantic for the next several
days.

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...Previous Discussion...

The latest NCEP surface analysis indicates a cold front over the
NT1 offshore waters this morning, and current surface
observations indicate up to 25 kt in the cold advection behind
the front. In addition, Ascat wind retrievals from last night
indicated up 30 kt ahead of the front with a few gales E of the
offshore waters. The 00Z GFS first sigma winds are initialized
well when compared with the current data, and picked up on the
higher winds near the front. The model indicates the front will
move through the NT1 offshore waters this morning before
stalling over the nrn NT2 waters this afternoon. The 00Z
ECMWF/UKMET/NAM/ GEM all agree well with the GFS on the timing,
though the GFS is a bit stronger with the winds in the cold
advection. The GFS indicates up to 30 kt over nrn NT2 and SW NT1
later today in the NE flow as high pres builds over the nrn
zones. This seems reasonable, so planning on starting out with
the 00Z GFS first sigma winds into 06Z tonight.

The 00Z models all indicate another weaker cold front will move
E across the area Fri night with winds up to 30 kt in SW flow
ahead of the front. This is close to the intensity of the
previous wind grids which went up to 25 kt, though the 00Z
ECMWF/UKMET are both a bit weaker and only show 25 kt. However,
this may be a tad underdone, especially with a developing low
level jet along the front so preferring to trend a little
stronger with the winds near this system. As a result, planning
on using a 2 to 1 blend of the previous grids and the 00Z GFS as
a compromise. This will briefly increase the winds in a few
outer NT2 zones to 30 kt on Fri night.

The 00Z models then indicate a stronger low pres system will
move through the area Sun into Sun night, with the 00Z GFS
showing a brief period of gales in the Gulf of Maine in the SE
flow ahead of the warm front. The GFS indicates another
developing level jet ahead of the warm front, with up to 45 kt
at 925 mb. Despite the stable conditions over the colder waters
in the Gulf of Maine, this should act to induce vertical mixing
in the sheared environment. The 00Z ECMWF only indicates about
25 kt, while the 00Z UKMET/GEM both indicate large areas with 30
kt in the outer waters. The previous forecast had gales in the
Gulf of Maine and Georges Bank for Sun into early Sun night.
Confidence is near average with the gales as a result of the GFS
remaining consistent on this scenario, so planning on staying
with the previous headlines in the next forecast. For the wind
grids, am planning on staying with previous grids to maintain
headlines for late Sun and Sun night. Will then transition to
the 00Z GFS winds from 09Z Sun through the remainder of the
forecast period. However, will boost 10 percent above the
guidance to account for the low wind bias the model has
exhibited this season in cold advection as the models generally
agree on the front moving SE through the area in the medium
range.

.Seas...The 00Z Wavewatch is initialized a little low in the
cold advection in cold advection in NT1, and seems a bit slow
with building seas in the NE flow later today and tonight. As a
result, planning on blending in the 00Z Wavewatch with the
previous wave height grids, but will boost slightly in the the
NE flow. Will continue with this blend through the forecast
period, mainly to maintain continuity while adjusting for the
00Z model trends. Will also boost slightly in cold advection to
account for the low bias of the Wavewatch.

.Extratropical Storm Surge Guidance: The 00Z ESTOFS is almost
twice as high as the 00Z ETSS with the surge forecast to develop
over Long Island Sound Sun in the strong easterly flow. The
ESTOFS shows about a 1.5 ft surge, while the ETSS is near 0.8
ft. These higher values my be underdone, based on the latest
probabilistic ETSS whose mean values are about the same as the
ESTOFS output here.

.WARNINGS...Preliminary.

.NT1 New England Waters...
.ANZ800...Gulf of Maine...
     Gale Possible Sunday into Sunday night.
.ANZ805...Georges Bank west of 68W...
     Gale Possible Sunday.
.ANZ900...Georges Bank east of 68W...
     Gale Possible Sunday.

.NT2 Mid-Atlantic Waters...
     None.

$$

.Forecaster Clark/Kells. Ocean Prediction Center.



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