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AGNT40 KWNM 301210

Marine Weather Discussion for N Atlantic Ocean
NWS Ocean Prediction Center Washington DC
810 AM EDT Thu Mar 30 2017

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

As the low pressure center SE of Nova Scotia continues to
intensify, the Nly gradient in its wake is likely still
supporting winds up to gale force across the far SE NT1 and far
NE NT2 waters at the moment. Max seas over this area are likely
in the low/mid teens which are being handled slightly better by
the 00Z ECMWF WAM versus the 06Z Wavewatch III at the moment.

Over the short term, the latest models forecast marginal gales to
continue across the far NE NT2 waters today, then become subgale
tonight as the strong low is forecast to move off to the E which
will allow its associated Nly gradient to weaken from W to E into
Fri. Then late Fri, the models have converged towards a similar
forecast track for the next developing surface low to approach
the Delmarva, then track E across the far Nrn NT2 waters Sat into
Sat night. So with the 06Z GFS remaining very consistent, see no
reason to make any major changes to the previously populated 00Z
GFS solution for this system.

In the long range, the most signficant forecast problem will
become how strong will a Sly gradient associated with a warm
fropa become Mon night across the NT2 waters. Per the 06Z/00Z GFS
in particular, can not rule out the possibility of gales
developing in this gradient, especially in the vicinty of the
gulf stream. But with this being day 5, for now still believe it
will be wise to continue to use the previously populated
GFS/ECMWF compromise and hold off on possible warnings.


The 0050Z and 0140Z Ascat overpasses confirmed gales across
southeastern Georges Bank (ANZ900) as well as the ANZ905 waters
south of Georges Bank, which was in line with the 00Z GFS first
sigma level winds. Based on the most recent model guidance, will
be carrying these gale warnings over the above zones through
much of the morning. The rapidly intensifying surface low east
of Georges Bank was centered near 44N59W at 06Z. As the vigorous
upper level trough continues to dig southeast south of Nova
Scotia this morning, and then phases with the strong upper low
lifting northeast out of the subtropics this evening, will see
the rapid deepening of the surface low and the significant
expansion of the gale to potentially hurricane force winds today
into Friday. the 00Z models are consistent that a north to south
oriented high pressure ridge will drift east across the NT1 and
NT2 waters today into Friday.

The 00Z models then are in general agreement that the wrapped up
closed upper level low currently over the Central Plains and
approaching the Mid Mississippi Valley will move eastward and
emerge off the mid Atlantic coast late Friday night/early
Saturday morning. The 00Z GFS/UKMET/CMC are ever so slightly
more progressive than the 00Z ECMWF/NAM. The 00Z models have
come into much better agreement with the track of the assoicated
surface low to move off the New Jersey coast late Friday night
and pass just south of Long Island Saturday. Also, compared to
its previous few runs, the 00Z GFS has is a bit stronger with
the low and its associated winds, which is a preferred trend.
However, the 00Z ECMWF continues to be about 4 to 6 mb deeper
than the 00Z GFS (EMSL field) with the central pressure of the
surface low. Nonetheless, the GFS and ECMWF winds are
comparable. By late Saturday night and early Sunday, the 00Z GFS
appears to drop the gales across the southeastern NT1 and far
northeastern NT2 waters too quickly. For wind grids through
Friday night, will use our smart tool which will incorporate the
00Z GFS first sigma level over areas with unstable low levels,
and 10m winds over stable areas. Then due to the model
differences noted above, elected to use an even blend of the 00Z
GFS first sigma level winds and 00Z ECMWF surface winds Saturday
through Sunday. Some minor adjustments were made to these
blended winds to keep continuity with the gales forecast this
weekend. The guidance is consistent with another high pressure
ridge passing east across the waters Sunday night into Monday
night. Later Monday and Monday night, would favor a compromise
00Z GFS/ECMWF solution for a warm front to lift Nwd across the
NT2 waters with a strengthening pre frontal gradient developing.
So for this compromise, will transition to populating with a
50/50 blend of the 00Z GFS first sigma/10m and 00Z ECMWF surface
winds at that time. For now will limit these southerly winds to
30 kt given the inherent forecast uncertainty at day5,
especially in these southerly flow events such as is forecast.

.Seas...Within the strong to gale force northerlies across the
outer offshore waters this morning, the 00Z ECMWF WAM did appear
to better initialized than the 00Z Wavewatch as indicated by a
23Z/29 Altika altimeter pass. Will conintue to use 50/50 blend
of this guidance through the near term. The 00Z ECMWF WAM is on
average 3 to 4 ft higher than the 00Z Wavewatch III late Friday
through Saturday night. Again a 50/50 blend seems justified
here, and will populate with this blend through the remainder of
the forecast period given our preference for the GFS/ECMWF blend
for winds in the medium range.



.NT1 New England Waters...
.ANZ805...Georges Bank west of 68W...
     Gale Friday night.
     Gale Possible Saturday into Saturday night.
.ANZ900...Georges Bank east of 68W...
     Gale Possible Saturday into Saturday night.
.ANZ810...South of New England...
     Gale Friday night.
     Gale Possible Saturday into Saturday night.
.ANZ815...South of Long Island...
     Gale Friday into Friday night.
     Gale Possible Saturday into Saturday night.

.NT2 Mid-Atlantic Waters...
.ANZ820...Hudson Canyon to Baltimore Canyon...
     Gale Friday into Friday night.
.ANZ915...Hudson Canyon to the Great South Channel...
     Gale Friday night.
     Gale Possible Saturday into Saturday night.
.ANZ920...Baltimore Canyon to the Great South Channel...
     Gale Friday night.
     Gale Possible Saturday into Saturday night.
.ANZ905...The Great South Channel to the Hague Line...
     Gale today.
     Gale Friday night.
     Gale Possible Saturday into Sunday.
.ANZ910...East of the Great South Channel and south of 39N...
     Gale Friday night.
     Gale Possible Saturday into Sunday.
.ANZ925...Outer Waters from Baltimore Canyon to Hatteras Canyon...
     Gale Friday into Friday night.
     Gale Possible Saturday into Saturday night.
.ANZ930...Outer Waters from Hatteras Canyon to Cape Fear...
     Gale Friday.


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