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000
AGNT40 KWNM 230107
MIMATN

Marine Weather Discussion for N Atlantic Ocean
NWS Ocean Prediction Center Washington DC
907 PM 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.

The latest model guidance indicates that low pressure currently
over the southeastern U.S. will move into the northern nt2 waters
by Tuesday night while strengthening. Southerly winds currently
up to 20 knots across the offshore waters will increase to
minimal gales by Tuesday night across portions of the nt2 waters.
The gales will then continue into early Wednesday. Another low
will then move into the Mid Atlantic region Wednesday night with
gales again expected in the nt2 waters ahead of the associated
cold front. The gales will then continue into Friday as the
surface low moves northeast across the nt1 waters. Winds should
then diminish across the offshore waters by Saturday. For wind
grids will continue to use the current grids throughout the
forecast period. Current warnings look reasonable and few changes
should be needed on the next offshore waters forecast.

For wave height grids will also continue to use the current grids
throughout the forecast period.

Extratropical storm surge guidance...n/a.

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

Over the short term, the new 12Z models have come into somewhat
better agreement in regards to what is expected to be a complex
synoptic pattern. The models all forecast the warm front now
extending off the N Carolina coast to lift slowly NEwd tonight
into Tue night. Then, with generally minor timing and/or track
differences, the models also foreast a low to develop on the
front tonight, then track NE across the Nrn NT2 and NT2 waters
Tue/Tue night with only moderately strong (generally up to 20-25
kt) associated gradients. Overall, would favor a solution closest
to the slightly more consistent 12Z UKMET/ECMWF (the 12Z GFS
looks a little too slow with the frontal low) for this warm fropa
and its low. Therefore, will populate our forecast wind grids
with the 12Z ECMWF boundary layer (BL) winds for tonight/Tue.

Then the 12Z models have converged towards a more similar
solution for another surface low to move to the mid Atlantic
coast late Tue, track NE across the NW NT2 waters Tue night, then
pass NE across Georges Bank Wed while pulling a trailing cold
front across the Nrn/central NT2 waters. In the SWly gradient in
advance of this front, similar to its previous respective runs,
the 12Z GFS/NAM/GEM all forecast gale force boundary layer (BL)
winds to develop forecast to develop across the NT2 waters
primarily from the gulf stream Swd. With the usually conservative
12Z UKMET/ECMWF also forecasting more limited gale force BL
winds, have relatively high forecast confidence that gale
warnings will be warranted. So as a compromise, plan on
populating with a 50/50 blend of 12Z GFS first sigma/10m winds
(time shifted 3 hours slower to line up better) and 12Z ECMWF
boundary layer winds on Tue night and Wed, with some subsequent
additional edits mainly to maintain the continuity of the
previously forecasted gale warnings.

In the long range, though they differ somewhat in regards to
their forecast tracks of the associated attendant surface low
tracking inland across the NE conus, the 12Z global models
overall share similar forecast timing for a cold front to push
offshore late Wed night into the far SW NT2 waters, continue
slowly offshore Thu/Thu night, then pass E of NE most NT2 waters
early Fri. Overall, would favor the similar 12Z GFS/UKMET/ECMWF
forecasting timing, while the 12Z GEM looks a little too
progressive. In regards to the associated forecast gradients with
this front, again all of the 12Z global models forecast gale
force BL winds to develop in the Sly prefrontal gradient across
the NT2 waters (primarily from the gulf stream Swd) late
Wed/early Wed night, and then persist through Thu night.
Therefore, have moderate to high forecast confidence in these
gales forming. So on Wed night through Fri night, plan on
continuing to populate with a 50/50 blend of 12Z GFS first
sigma/10m winds (time shifted 3 hours faster again to line up
better) and 12Z ECMWF boundary layer winds. Then prefer the 12Z
ECMWF solution on Sat/Sat night, so will populate with all 12Z
ECMWF BL winds then.

.Seas...The 12Z Wavewatch III or 12Z ECMWF WAM have both
initialized the current seas well. Since the 12Z ECMWF solution
will be favored initially, will populate our forecast wave grids
with 12Z ECMWF WAM seas for tonight and Tue. Then since a blend
of their associated 12Z GFS/ECMWF solutions will be used, will
populate a 50/50 blend of the similar 12Z Wavewatch III and 12Z
ECMWF WAM seas for Tue night through Fri night (with the
Wavewatch III seas time shifted the same as was done with the GFS
winds). Then since the 12Z ECMWF will become favored on Sat/Sat
night, will populate with all 12Z ECMWF WAM seas then.

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

$$

.Forecaster Nolt/Vukits. Ocean Prediction Center.



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