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000
AGNT40 KWNM 211410
MIMATN

Marine Weather Discussion for N Atlantic Ocean
NWS Ocean Prediction Center Washington DC
910 AM EST Tue Feb 21 2017

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

Grids: 00Z GFS into the 23/12Z, then a 1:1 blended 00Z GFS/ECMWF
solution thereafter. Discussion follows.

As far as February is concerned, a rather quiet few days on the
horizon as high pressure settles over the West Atlantic through
Wednesday night, resulting in mostly calm winds and flat seas
across the bulk of OPC waters. The high will slowly shift east
of the area Thursday and Thursday night, as low pressure races
quickly east across Quebec and New Brunswick dragging a cold
front into the northern waters. The cold front should only make
it to about 40N by Friday morning, stall, then lift back north as
a warm front Friday night ahead of an approaching strong cold
front. Across the NT2 waters, southern stream closed upper low
will move across Florida Wednesday night and Thursday, lift north
and northeast across the waters Friday, then dissipate or become
absorbed into passing cold front sweeping across the entire area
Saturday and Saturday night.

Models remain in remarkably good agreement throughout most of the
forecast period, leading to high overall forecast confidence.
That being said, marginal gale headlines remain across the
southern and outer zones 930 and 935 along the north quadrant of
anomalous southern stream low Friday afternoon. With 06Z GFS
continuing to output possible gales, and in deference to
forecast continuity, will keep gale headlines in place for now.
With a slightly higher degree of confidence, gales in the
forecast Saturday night across the northern outer zones 905 and
910 ahead of approaching cold front.

Seas: previous shift opted for a 1:1 WW3/WAM blended solution to
iron out subtle differences between the mostly agreeable
significant wave height guidance.

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

Over the short term, an earlier 0152Z high resolution ASCAT-A
scatterometer pass confirmed that max winds in the Nly gradient
across the waters were up to 25-30 kt...highest across the NE
most NT2 waters near the gulf stream. The new 00Z models overall
remain in good agreement that this Nly gradient will steadily
weaken as a high pressure ridge slowly builds offshore today and
tonight, then shifts to a generally weak Sly gradient Wed into
Wed night as the ridge passes E of the offshore waters. So
similar to the previous offshore forecast package, plan on
populating our forecast wind grids with our smart tool that will
place representative 00Z GFS first sigma level winds in unstable
areas and weaker 00Z GFS 10m winds in stable areas for today
through Wed night, with some minor additional edits in deference
to the 00Z UKMET/ECMWF.

In the long range, similar to its previous 18Z run the 00Z GFS
continues to forecast a Srn stream surface low to approach the
NT2 waters from the S Fri, lift NNE into the Srn NT2 waters Fri
night, then dissipate Sat. Overall would favor a compromise 00Z
GFS/ECMWF forecast track for this system. In regards to the Ely
gradient gradient that is forecast to develop N of this low, the
00Z GFS remains consistent in forecasting gale force first sigma
level winds to develop across the outermost Srn NT2 waters Fri
into Fri night, which are supported by the 00Z GEM. With the
usually conservative 00Z ECMWF forecasting solid 25-30 kt
boundary layer winds in this gradient, will go ahead and maintain
the previously forecasted gale warnings, with low/moderate
forecast confidence. Then further out in the long range, the 00Z
GFS/ECMWF now share similar timing for a strong cold front to
sweep offshore late Sat/Sat night, which is more progressive than
the 00Z GEM/UKMET. For now since they are more in line with the
latest WPC Medium Range guidance, would favor a compromise 00Z
GFS/ECMWF forecast timing for this fropa. SO as a compromise in
the long range, will populate with a 50/50 blend of the 00Z GFS
first sigma/10m and 00Z ECMWF boundary layer winds for Thu
through Sat night.

.Seas...A compromise between the slightly higher 00Z ECMWF WAM
and the 00Z Wavewatch III initializes the current seas best at
the moment. With this in mind for the short term, and then since
a compromise 00Z GFS/ECMWF solution will be favored in the long
range, will populate our forecast wave grids with a 50/50 blend
of the 00Z Wavewatch and 00Z ECMWF WAM for today through Sat
night.

.Extratropical storm surge guidance...N/A.


.WARNINGS...Preliminary.

.NT1 New England Waters...
     None.

.NT2 Mid-Atlantic Waters...
.ANZ905...The Great South Channel to the Hague Line...
     Gale Possible Saturday night.
.ANZ910...East of the Great South Channel and south of 39N...
     Gale Possible Saturday night.
.ANZ930...Outer Waters from Hatteras Canyon to Cape Fear...
     Gale Possible Friday.
.ANZ935...Outer Waters from Cape Fear to 31N...
     Gale Possible Friday.

$$

.Forecaster Collins/Vukits. Ocean Prediction Center.



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