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956
AGNT40 KWNM 221201
MIMATN

Marine Weather Discussion for N Atlantic Ocean
NWS Ocean Prediction Center Washington DC
801 AM EDT Mon May 22 2017

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

A relatively quiet weather pattern persists at the moment. High
pressure over the NT1 waters is combining with a stationary front
across the Srn NT2 waters to support a weak (generally 15-20 kt,
or less) ESE gradient N of the front across the NT2 waters. Max
seas throughout Max seas in this gradient are likely only in the
4-6 ft range which are being handled fine by the 06Z Wavewatch
III and 00Z ECMWF WAM models at the moment.

Over the short term, the latest models present no major forecast
problems. The models in general agree that the front will slowly
lift NEwd as a warm front later today into Tue night with a
frontal wave developing on the front and tracking NEwd. The 00Z
ECMWF remains consistent in forecasting the strongest frontal
wave of all of the models. For now would continue to favor the
previous populated 00Z GFS/ECMWF compromise for this fropa and
frontal wave and will continue to expect moderately strong (up to
20-25 kt) associated gradients. Then Tue night into Wed, with
timing differences, the models forecast another surface low to
exit the mid Atlantic coast and track NE across the waters
causing a strengthening Sly gradient to develop to its S (with
gale force boundary layer winds across the NT2 waters primarily
from the gulf stream Swd). The 06Z GEFS Mean indicates that the
06Z GFS may be too fast with this low. Therefore would continue
to favor the previously used 00Z ECMWF solution, which is
supported by the 00Z GFS. So do not plan on making any major
short term changes in the next offshore forecast package.

In the long range, in general the latest global models continue
to agree that the most significant feature will be a cold front
slowly pushing offshore Thu/Thu night, then passing E of the
offshore waters Fri with again a gale force Sly prefrontal
gradient developing across the NT2 waters from the gulf stream
Swd. So with the 06Z GFS providing support, will continue to use
the previously populated 00Z GFS/ECMWF compromise solution for
this fropa, with just some additional minor edits in deference to
the 06Z GFS and 00Z ECMWF.





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

At 06Z surface analysis shows a stationary front across the
southern NT2 waters. High resolution 0050Z and 0230Z ASCAT-A and
0142Z ASCAT-B scatterometer passes confirmed max winds were up to
up to 20-25 kt in the easterly gradient across the central and
north-central NT2 waters with the highest conditions near the
Gulf Stream. The new 00Z models remain consistent in forecasting
the front to begin moving Nwd as a warm front today with the Ely
gradient weakening a bit in response to the high pressure ridge N
of the front weakening while moving east. Then late today
through Tue the models generally agree that the front will return
Nwd as a warm front while a frontal wave tracks NE along the
front with a moderately strong, in the 15-25 kt range, SSE
associated gradient spreading Nwd in the vicinity of the front
and the wave. Therefore, similar to the previous offshore
forecast package, plan on populating our forecast wind grids for
today with the representative 00Z GFS solution by using our smart
tool that will place stronger GFS first sigma level winds in
unstable areas and weaker GFS 10m winds in stable areas (mainly
north of the Gulf Stream). Then as a compromise, will populate
winds with a 50/50 blend of the 00Z GFS first sigma/10m winds and
00Z ECMWF boundary layer (BL) winds tonight and Tue.

Then similar to its previous respective runs, the 00Z GFS
forecasts a surface low with a warm front to move NE off the mid-
Atlantic coast Tue night, then weaken out over the Nrn NT2 and
east of Georges Bank by late Wed/Wed night with gale force
boundary layer (BL) winds forecast to develop in the SWly
gradient immediately S of the low and front. The 00Z NAM
supports this GFS solution, but appears overdone with gale force
gradient north of the low. The 00Z ECMWF and especially
00ZGEM/UKMET all forecast their surface lows to track further NW
then N pulling their warm fronts further N than the GFS. With
the 00Z GEFS Mean indicating that the 00Z GFS track is perhaps
too far S, would favor a solution closer to the 00Z GEM/ECMWF
for this system, and Wed to Wed night the 00Z UKMET which is
also more in line with the latest WPC Medium Range guidance.
Therefore, will populate with 00Z ECMWF BL winds Tue night and
then 00Z UKMET BL winds Wed and Wed night.

Then though they continue to differ in regards to their forecast
track of the associated attendant surface low, the 00Z models in
general agree that a cold front to sweep offshore Thu/Thu night,
then pass E of the offshore waters Fri. In regards to the
forecast timing of this frontal passage, would favor a
compromise between the similar 00Z GFS/ECMWF, which is supported
by the 00Z GEFS Mean. The 00Z UKMET looks like a fast outlier
with the front. In regards to the associated forecast gradients,
would again favor a blended 00Z GFS/ECMWF solution which would
result in possible prefrontal SSWly gales developing across the
NT2 waters S of the Gulf Stream. Therefore, plan on populating
with a 50/50 blend of 00Z GFS first sigma/10m and 00Z ECMWF
boundary layer winds on Thu through Fri night.

.Seas...The 00Z wave models have initialized reasonably well.
With the associated 00Z GFS/ECMWF solutions being similar, will
populate our forecast wave grids with a 50/50 blend of the
similar 00Z Wavewatch III and 00Z ECMWF WAM seas for today
through Tue. Then since the 00Z ECMWF solution will become
favored, will transition to populating with all 00Z ECMWF WAM
Tue night. Then for Wed and Wed night when UKMET us used will
use 75 percent 00Z ECMWF WAM and 25 percent 00Z NWW3 and then on
Thu through Fri night will transition back to populating with a
50/50 blend of the two wave models.

.Extratropical Storm Surge Guidance...N/A.


.WARNINGS...Preliminary.

.NT1 New England Waters...
     None.

.NT2 Mid-Atlantic Waters...
.ANZ920...Baltimore Canyon to the Great South Channel...
     Gale Possible Wednesday into Wednesday night.
.ANZ910...East of the Great South Channel and south of 39N...
     Gale Possible Wednesday.
     Gale Possible Thursday night.
.ANZ828...Inner Waters from Cape Charles Light to Currituck Beach Light...
     Gale Tuesday night.
     Gale Possible Wednesday.
.ANZ925...Outer Waters from Baltimore Canyon to Hatteras Canyon...
     Gale Tuesday night.
     Gale Possible Wednesday.
.ANZ830...Inner Waters from Currituck Beach Light to Cape Hatteras...
     Gale Tuesday night.
     Gale Possible Wednesday.
.ANZ833...Inner Waters from Cape Hatteras to Cape Fear...
     Gale Possible Wednesday night into Thursday.
.ANZ930...Outer Waters from Hatteras Canyon to Cape Fear...
     Gale Tuesday night.
     Gale Possible Wednesday.
     Gale Possible Thursday night.
.ANZ835...Inner Waters from Cape Fear to 31N...
     Gale Possible Wednesday into Thursday.
.ANZ935...Outer Waters from Cape Fear to 31N...
     Gale Possible Thursday into Thursday night.

$$

.Forecaster Vukits/Bancroft. Ocean Prediction Center.



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