AGNT40 KWNM 191429
MIMATN

Marine Weather Discussion for N Atlantic Ocean
NWS Ocean Prediction Center Washington DC
1029 AM EDT Sat Sep 19 2020

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

The GOES visible satellite imagery shows a strong cold front
across the offshore waters this morning, and strong high
pressure building E into New England. This setup has created a
hazardous situation, as the pressure gradient N of the front has
tightened as the high is interacting with the front. Ascat from
overnight showed some gales in NT2 N of the front, with the
higher conditions in the unstable conditions over the Gulf
Stream. The 00Z/06Z models all show the gradient remaining tight
across the offshore waters through Mon as the high continues
building over New England as the front drifts to the E. Also,
the models and the last NHC advisory for Hurricane Teddy indicate
the system will move N over the next few days, and pass just E of
the NT2 waters late Mon into Tue. The previous forecast had gales
up in the short range associated with the front, while tropical
storm headlines eventually reach the outer zones in NE NT2 and
far SE NT1 late Mon into Tue. The 06Z models have not changed
significantly from the 00Z cycle into Tue, so confidence with
previous headlines remain above average with the models in good
agreement. As such, am planning on continuing previous headlines
in the update package, although will be making adjustments based
on the 11 AM EDT advisory from NHC when issued.

In addition, the 00Z/06Z wave models show fairly heavy seas building
in the offshore waters in conjunction with the higher winds. A
1030 UTC altimeter pass from just S of Cape Hatteras retrieved
values up to 16 ft in the strong NE flow, and was not in the area
where the models indicated the max values. As such, the guidance
is initialized a tad low, so will stay near previous wave height
grids which were adjusted higher to match up with current
conditions. Otherwise, am not planning on making any significant
changes through the remainder of the forecast period.

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PREVIOUS DISCUSSION...

Mariners should continue to use extreme caution over the next few
days as widespread gales and very rough waves dominate a good
portion of the offshore waters.

Many of the observations off the Mid-Atlantic coast indicate
N and NE wind gusts near and above gale force occurring to the N
and W of a cold front crossing the far eastern outer central and
southern NT2 offshore waters early this morning. The ASCAT
overpasses from last evening also indicated winds over this
region near gale force. Scattered thunderstorms are now moving
mostly E of the offshore waters with the strong cold front, but
there will still be a threat for a few thunderstorms mainly over
the far eastern NT2 and far southern NT2 waters today with gusty
winds and rough seas in and near any thunderstorms. Overall, the
00Z guidance remains in very good agreement and has remained
quite consistent over the region into early Mon. We will
populate grids over this time frame with the 00Z GFS winds and
use the stability tool to place the stronger first sigma layer
winds where the conditions more the most unstable, and then also
add up to 10 percent or so to the winds over the gulf stream,
which will help to maintain the previous hazards for the early
morning package into early Mon. Conditions during the day Mon
through Tue and even into Tue night become more dependent on the
National Hurricane Center's latest advisory for Hurricane Teddy
which is forecast to pass E of the offshore waters at that time,
with tropical storm conditions spreading westward into portions
of the eastern NT1 and NE NT2 waters. Please monitor the latest
NHC information regarding Teddy over the next few days, with
additional adjustments to the ongoing OPC forecast quite possible
at this time.

Otherwise, all mariners should use extreme caution especially in
and near the gale areas, with the strong counterflow to the gulf
stream expected to persist for the next few days, and remain
quite strong for most of the time into early next week along and
off the Mid-Atlantic and SE U.S. coast. This will result in
extremely steep and breaking large waves, and a building large
sea state throughout the weekend and even early next week again
mainly off the Mid-Atlantic and SE coast. The forecast for most
of Mon into Tue night will be adjusted once the 5 AM EDT advisory
from NHC for Hurricane Teddy arrives. For Wed and Wed night, we
still forecast improving conditions as high pressure slides E off
the SE U.S. coast, and for that time frame we will populate
grids with an even blend of the 00Z ECMWF bias corrected winds
and 00Z GFS winds. Forecast confidence into early Mon is above
average, and then closer to average thereafter.

Seas: Sea heights continue to build over the offshore waters this
morning as the N and NE wind field in the wake of the cold front
increases and expands over the area. Sea heights range up to 14
ft or so near the north wall of the gulf stream off the southern
Delmarva coast, to near 6 ft or so over the far northern and
southern portions of the offshore waters. Sea heights will
continue to build especially over the NT2 waters through Sun into
Mon, and then potentially over New England waters by Mon through
Tue night as Hurricane Teddy moves towards Nova Scotia and SE
Canada. Sea heights over 20 ft are likely over a good portion of
the offshore waters by tonight and Sun into next week. For the
early morning package, we will remain close to the previous sea
height grids into Mon, and adjust them in deference to nearby
coastal WFO and TAFB grids, as they indicate the enhanced sea
heights likely over and near the gulf stream through early parts
of next week. Sea heights by Mon night and Tue night will be
adjusted based on the 5 AM NHC Advisory for Teddy, and then by
Wed and Wed night we will use an even blend of the 00Z Wavewatch
and 00Z WAM to match the winds by day 5 and beyond.

Again, all marine interests should continue to closely monitor
the latest NHC advisory information and OPC forecasts through the
weekend.

.EXTRATROPICAL STORM SURGE GUIDANCE...The latest ESTOFS remains
generally consistent in developing a 1 to near 2 ft surge along
the Mid-Atlantic coast from the New Jersey coast southward
through early next week, with another surge possible further N
depending on the track of Hurricane Teddy early next week. The
duration of the surge event could accentuate any potential
coastal flooding problems as it will take place over several high
tide cycles. Also, these surge guidance is likely at least
somewhat underdone in the strong, persistent, NE wind field.
Please see forecasts from local National Weather Service offices
for detailed tide and water level information.


.WARNINGS...Preliminary.

.NT1 New England Waters...
.ANZ805...Georges Bank west of 68W...
Gale Possible Monday into Monday night.
.ANZ900...Georges Bank east of 68W...
Gale Possible Monday.
Tropical Storm Possible Monday night into Tuesday.
.ANZ810...South of New England...
Gale Possible Monday into Monday night.

.NT2 Mid-Atlantic Waters...
.ANZ915...Hudson Canyon to the Great South Channel...
Gale Sunday night.
Gale Possible Monday into Monday night.
.ANZ920...Baltimore Canyon to the Great South Channel...
Gale today into Sunday night.
Gale Possible Monday into Monday night.
.ANZ905...The Great South Channel to the Hague Line...
Gale Sunday night.
Gale Possible Monday.
Tropical Storm Possible Monday night into Tuesday.
.ANZ910...East of the Great South Channel and south of 39N...
Gale today into Sunday night.
Gale Possible Monday.
Tropical Storm Possible Monday night into Tuesday.
.ANZ828...Inner Waters from Cape Charles Light to Currituck Beach Light...
Gale today into Sunday night.
.ANZ925...Outer Waters from Baltimore Canyon to Hatteras Canyon...
Gale today into Sunday night.
Gale Possible Monday into Monday night.
.ANZ830...Inner Waters from Currituck Beach Light to Cape Hatteras...
Gale today into Sunday night.
.ANZ833...Inner Waters from Cape Hatteras to Cape Fear...
Gale today into Sunday night.
.ANZ930...Outer Waters from Hatteras Canyon to Cape Fear...
Gale today into Sunday night.
Gale Possible Monday.
.ANZ835...Inner Waters from Cape Fear to 31N...
Gale today into Sunday night.
.ANZ935...Outer Waters from Cape Fear to 31N...
Gale today into Sunday night.
Gale Possible Monday.

$$

.Forecaster Kells/Mills. Ocean Prediction Center.