North Atlantic Marine Weather Discussion

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AGNT40 KWNM 201400
MIMATN

Marine Weather Discussion for N Atlantic Ocean 
NWS Ocean Prediction Center Washington DC 
900 AM EST SUN 20 JAN 2019 

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

Gale force winds have likely developed this morning across the 
Mid-Atlantic offshore waters, and are expected to become more 
widespread this afternoon and evening. Recent observations 
across the Gulf of Maine are also supporting the presence of 
gale force winds. In addition, recent buoy reports are 
indicating wave heights in the 11 to 14 ft range extending 
across the Gulf of Maine to just north of Cape Cod Bay. The 
latest models continue to consistently advertise storm force 
winds developing across the northern outer NT2 zones, and as a 
result our confidence with these hazards. Also, the latest model 
soundings support a deep enough mixed layer to get some storm 
force winds to the surface over these warmer Gulf Stream waters 
this afternoon into this evening. The GFS and ECMWF have been 
consistent with the strengthening low level jet, to 65 to 85 kt 
across these outer zones. The 00Z ECMWF was then stronger than 
the 00Z/06Z GFS with peak winds through the mixed layer in the 
strong cold air advection Mon afternoon and Mon night. The 
previous offshore wind grids appear on target and we will not be 
making significant changes with this mornings forecast updates.  


Both the 06Z Wavewatch and 00Z ECMWF WAM are at least a few ft 
too low with the wave heights across the Gulf of Maine this 
morning. Across the mid-Atlantic offshore waters, a blend of the 
aformentioned models would best capture the current sea state 
this morning. The 00Z ECMWF WAM appears slightly too high, while 
the latest Wavewatch is a few ft low here as well. Water levels 
from the Virginia tidewater area north to Woods Hole and 
Nantucket, including Long Island Sound, are running about 1.5 ft 
to 2 ft higher than predicted levels which suggest that the ETSS 
and to a somewhat lesser extent, the ESTOFS, are underdone with 
the storm surge impacting the coast this morning.    

---------------------------------------------------------------
...Previous Discussion...

Over the short term, today through Mon, we will not make major 
adjustments to the ongoing OPC forecast and hazards with the 00Z 
model guidance remaining very consistent, and in good overall 
agreement over the next 24-48 hours. We will populate grids with 
a 90 percent previous grid, 10 percent Warw blend, and make a 
few minor edits to maintain the previous hazards. ASCAT 
overpasses from last evening between 0055Z and 0235Z indicated 
maximum winds around 30 kt off coast from southern New England 
southward. A strong low pressure center is still forecast to 
track NE from West Virginia early this morning, to near NYC by 
midday, to the Gulf of Maine by 00Z Mon. An associated warm 
front will continue to move N from the northern NT2 waters 
today, with an increase in thunderstorms likely S of the warm 
front, and ahead of the an Arctic cold front which trails S and 
SW from the low center. The latest radar, GOES-IR satellite 
imagery, and lightning data show scattered thunderstorms already 
developing from E of Delaware Bay, to E of Cape Hatteras and 
then extending SW to coastal Georgia and north Florida. The 
thunderstorm activity will likely increase over the offshore 
waters S of 40N or so today, with a few thunderstorms even N of 
40N near the warm front, with most of the thunderstorms moving E 
of the waters tonight as the Arctic front clears the region. 
Widespread gale to storm force winds are likely across the 
waters today into Mon, along with strong wind gusts locally near 
to exceeding storm force and very rough seas in and near any of 
the stronger thunderstorms. There also remains the chance for 
storm force winds developing near the north wall of the Gulf 
Stream by later Mon in the very strong cold air advection in the 
wake of the Arctic front. For now, it appears as if the best 
chance for storm force winds will be Mon evening, with 
additional adjustments to the forecast likely over the next day 
or so. Caution is advised for all of the offshore waters during 
the next 24-48 hours, with forecast confidence levels slightly 
above average. 

Over the medium range, we will trend the forecast toward the 
more consistent, and mostly in the middle of the 00Z model 
guidance, 00Z ECMWF model winds, and use the boost tool over the 
waters Mon night into Tue night. This will result in similar 
hazards to the past few OPC forecast, except to add storm force 
winds for a time early Mon night over the outer NT2 zone of 
ANZ910, which is near the north wall of the Gulf Stream, and has 
a good chance for seeing storm force winds in the strong cold 
air advection over this region. There is some chance for storm 
force winds over the adjacent zones Mon night, but for now we 
will only show them for this zone, and continue to evaluate 
future guidance. The strong cold air advection will persist into 
Tue into Tue night over the waters while slowly shifting 
eastward as high pressure builds from the Ohio Valley E and SE, 
reaching the coast by Tue evening, and overspreading the waters 
later Tue night. The high will then move E away from the waters 
Wed as the next low pressure system pushes E from the Midwest. S 
and SW winds will develop and increase over the waters Wed, then 
increase further ahead of the approaching low pressure system 
Wed night with gale force winds developing over central and 
southern NT2 waters, which is very similar to the past few OPC 
forecasts. For Thu, we expect developing low pressure to move 
from near the Jersey Shore NE to the Maine coast, and then move 
toward the Canadian Maritimes Thu night with a trailing cold 
front passing E and SE over the waters. For now, it appears that 
gales will occur ahead of the front, with a chance for storm 
force winds as well, especially near the Gulf Stream. For now, 
we will keep winds below storm force, and continue to monitor 
the guidance over the next few days. Gales do not appear likely 
in the cold air advection in the wake of the front at this time 
as the advection will be limited as the associated upper level 
trough weakens over the western North Atlantic, and re-develops 
further W back over the Great Lakes and Plains States. Forecast 
confidence is near average over the medium range time frame. 

Seas...The 00Z Wavewatch appears to be initialized about 1-2 ft 
too low over the waters early this morning, while the 00Z ECMWF 
WAM is running up to 2 ft too high, with the previous grids 
running close to the latest observations over the offshore 
waters. Sea heights range from around 10 ft off the SE coast to 
8 ft off the New England coast early this morning. For the early 
morning package, we will use a 75 percent previous grid, 25 
percent 00Z WAM blend for most of today into Tue night, and then 
transition more toward the 00Z WAM For Wed through Thu night to 
best match the wind forecast. We will also reduce sea heights up 
to 15-20 percent for Thu and Thu night over the waters, as was 
done in the previous few OPC forecast, as these forecast sea 
heights appear to better match the wind forecast later in the 
week. 

.EXTRATROPICAL STORM SURGE GUIDANCE: The 00Z ESTOFS and ETSS 
both show a positive surge greater than 1.5 ft along the 
northern mid-Atlantic and New England coasts today with the 
increasing easterly, then southerly flow ahead of the developing 
coastal low. Our confidence is a bit low in the surge models, 
with the GFS winds looking a bit underdone especially in the 
easterly flow. The ESTOFS continues to be up to a foot higher 
than the ETSS which appears more likely; however, we are still 
concerned that even these values are still underdone. The 
positive surge values will then diminish tonight as winds become 
offshore and increase with an increasingly negative surge 
developing later tonight through Mon. Another positive surge may 
develop by later Wed and Thu ahead of the next low pressure 
system as southerly winds increase over the waters. Please 
monitor the latest advisories, warnings, forecasts and 
statements from coastal National Weather Service forecast 
offices for more details. 

.WARNINGS...Preliminary. 

.NT1 New England Waters...
.ANZ800...Gulf of Maine...
     Gale today.
     Gale Monday night.
     Gale Possible Tuesday.
     Gale Possible Thursday into Thursday night. 
.ANZ805...Georges Bank west of 68W...
     Gale today into Monday night. 
     Gale Possible Tuesday.
     Gale Possible Thursday into Thursday night. 
.ANZ900...Georges Bank east of 68W...
     Gale today into Monday night. 
     Gale Possible Tuesday into Tuesday night. 
     Gale Possible Thursday into Thursday night. 
.ANZ810...South of New England...
     Gale today into Monday night. 
     Gale Possible Tuesday.
     Gale Possible Thursday into Thursday night. 
.ANZ815...South of Long Island...
     Gale today into Monday night. 
     Gale Possible Tuesday.
     Gale Possible Thursday.

.NT2 Mid-Atlantic Waters...
.ANZ820...Hudson Canyon to Baltimore Canyon...
     Gale today into Monday night. 
     Gale Possible Thursday.
.ANZ915...Hudson Canyon to the Great South Channel...
     Gale today into Monday night. 
     Gale Possible Tuesday.
     Gale Possible Thursday into Thursday night. 
.ANZ920...Baltimore Canyon to the Great South Channel...
     Storm today into tonight. 
     Gale Monday into Monday night. 
     Gale Possible Tuesday.
     Gale Possible Thursday into Thursday night. 
.ANZ905...The Great South Channel to the Hague Line...
     Storm today into tonight. 
     Gale Monday into Monday night. 
     Gale Possible Tuesday into Tuesday night. 
     Gale Possible Thursday into Thursday night. 
.ANZ910...East of the Great South Channel and south of 39N...
     Storm today into tonight. 
     Gale Monday.
     Storm Monday night.
     Gale Possible Tuesday.
     Gale Possible Thursday into Thursday night. 
.ANZ825...Inner Waters from Baltimore Canyon to Cape Charles 
Light...
     Gale today into Monday night. 
     Gale Possible Thursday.
.ANZ828...Inner Waters from Cape Charles Light to Currituck 
Beach Light...
     Gale today into Monday night. 
     Gale Possible Wednesday night into Thursday night. 
.ANZ925...Outer Waters from Baltimore Canyon to Hatteras 
Canyon...
     Storm today.
     Gale tonight into Monday night. 
     Gale Possible Tuesday.
     Gale Possible Wednesday night into Thursday night. 
.ANZ830...Inner Waters from Currituck Beach Light to Cape 
Hatteras...
     Gale today into Monday night. 
     Gale Possible Wednesday night into Thursday night. 
.ANZ833...Inner Waters from Cape Hatteras to Cape Fear...
     Gale today into tonight. 
     Gale Possible Wednesday night into Thursday night. 
.ANZ930...Outer Waters from Hatteras Canyon to Cape Fear...
     Gale today into Monday night. 
     Gale Possible Thursday into Thursday night. 
.ANZ835...Inner Waters from Cape Fear to 31N...
     Gale today into tonight. 
     Gale Possible Wednesday night into Thursday night. 
.ANZ935...Outer Waters from Cape Fear to 31N...
     Gale today into tonight. 
     Gale Possible Thursday into Thursday night. 

$$ 

.Forecaster Clark/Mills. Ocean Prediction Center.