marine weather discussion for N Atlantic Ocean NWS ocean prediction center Washington DC 936 am EST Tue Nov 20 2018
.Forecast discussion...Major features/winds/seas/significant .Weather for the North Atlantic ocean W of 50w from 30n to 50n.
A series of lows will pass over the northern waters and that will maintain a persistent tight pressure gradient over the northern waters that will keep elevated winds through most of the forecast period. NCEP weather map has low pressure 1010 mb over Baltimore Canyon with a cold front stretching southwest along the eastern edge of the central and southern outer waters. There are several lows along a frontal boundary that lies across the southeastern states to the mid Atlantic states. Farther west is another frontal boundary with lows and it stretches southwest from Nova Scotia through the Great Lakes into the states just northeast of Texas state. To the east of the waters is high pressure 1033 mb centered near 45n42w. Pressure gradient is just tight over the northern waters especially the far eastern portion where winds are just reaching gale force.
Seas are relatively small across the region with a peak at 7 ft over the far eastern portion of the Baltimore Canyon. Nww3 and ecmwfwave models fit very well the observed seas pattern. There are no major differences between the models in the short term and they both suggest seas will build over the central and northern waters in the short term.
Global models GFS/CMC/ecmwfhr/ukmethr have initialized fairly well the latest synoptic surface map with just small variations on the actual position of the lows along the frontal boundaries. In the short term, models differ slightly on the windspeed and also the areal coverage of winds in gale force range. Will favor model with stronger winds and also that has good coverage of gale force winds. Will not deviate from the previous model choice and so will stay with NAM initially then switch to ecmwfhr.
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Over the short term, we will remain close to the previous grids into this afternoon, as they appear to be very representative of the current winds over the offshore waters based on the latest observations and ascat overpasses from last evening. An ascat overpass did show a few gale force wind returns about 150 nm E of Virginia Beach at 0122z. We will maintain gales just S of the low pressure area producing these stronger winds for most of today as it tracks E-NE over the central, toward the NE nt2 waters, near the north wall of the Gulf Stream. GOES-IR imagery and lightning density data early this morning continue to indicate scattered thunderstorms occurring near the low, and then trailing SW along an associated cold front. The threat for thunderstorms is still forecast to diminish from W to E today, with another chance developing tonight into early Wed near a second cold front. Caution for local wind gusts near gale force and rough seas in and near any of the stronger thunderstorms. Otherwise, by later today into Wed, we will blend in some of the stronger 00z NAM winds to the ongoing grids, but for the most part maintain the previous hazards. The low mentioned above will move E-NE away from the NE nt2 waters tonight, with a second low developing and tracking NE near the New England coast today, moving E from the Gulf of Maine this evening with a small area of gales in the cold air advection to the W of the low pressure center over the Gulf of Maine later today and this evening. The low will intensify as it passes just S of Nova Scotia tonight, with the cold air advection the strongest over the Georges Bank into the NE nt2 waters we will maintain the previous gales over these waters for the early morning package, with good support from most of the 00z guidance. These gales will then likely push E of the offshore waters early Wed as a weak high pressure ridge slides E into the region. Forecast confidence over the short term is slightly above average.
Over the medium range, Wed night through Fri night, the 00z models remain in good agreement over the waters, with a strong Arctic cold front passing se over the waters Wed night, followed by Arctic high pressure building se over the East Coast from the Great Lakes Thu and Thu night. The high will then move se over the New England and northern mid-Atlantic waters Fri into Fri night. For the early morning package, we will use an even blend of the previous grids and boosted 00z ECMWF winds for Wed night through Fri night, with little change in hazards for the early morning package from the past few opc forecasts. Confidence is slightly above average over the region during this time frame. For Sat through Sun night, the 00z models continue to show very poor run-run continuity with regard to the timing, track and intensity of the low pressure system expected to impact the offshore waters. We will trend grids more toward the wpc medium range guidance, which for Sat into Sat night is very close to the 00z ECMWF and 00z UKMET guidance so we will populate using this mix of guidance for early Sat, then later Sat into Sat night respectively. By later Sat night through the rest of the period, wpc is close to the ECMWF ensemble mean, and we will follow along for now, but enhance winds by 10-15 percent to better match the guidance previously used for the forecast. As a result, we will expand gales off the se coast Sat into Sat night, and then as models diverge bring winds back below gale for late Sat night into early next week until better model agreement develops over the coming days.
Please continue to closely monitor the latest opc forecast over the next few days, with forecast confidence falling to below average over the weekend into early next week.
Seas...the previous opc sea height forecast appears to be verifying quite well when compared to the latest observations and altimeter data over the region with sea heights ranging from near 9 ft near the gale force wind area, to 2 to 3 ft closer to the East Coast. For the early morning package, we will rely on the previous grids with a few edits in deference to the nearby coastal WFO and TAFB grids today into Wed evening, and then use a 50/50 blend of the 00z ECMWF wam and 00z wavewatch for later Wed night into Sat over the waters, as it appears that the wam may be a little too high at times, with the wavewatch a little too low. For Sat night into early next week, we will attempt to blend sea heights to match the wind forecast as noted above with manual edits to best match coastal WFO grids.
.Extratropical storm surge guidance...No significant positive surge is expected along the New England and mid-Atlantic coasts during the few days. There is the potential for a possibly significant positive surge event developing next weekend over the region. Please closely monitor the latest opc and NWS coastal marine forecasts over the next few days.
.Nt1 New England waters... .anz800...Gulf of Maine... gale today into tonight. Gale Wednesday night. Gale possible Thursday into Thursday night. .Anz805...Georges Bank west of 68w... gale Wednesday night. Gale possible Thursday into Thursday night. .Anz900...Georges Bank east of 68w... gale tonight. Gale Wednesday night. Gale possible Thursday into Friday. .Anz810...South of New England... gale Wednesday night. Gale possible Thursday into Thursday night. .Anz815...South of Long Island... gale Wednesday night. Gale possible Thursday.
.Nt2 mid-Atlantic waters... .anz915...Hudson Canyon to the great South Channel... gale Wednesday night. Gale possible Thursday into Thursday night. .Anz920...Baltimore Canyon to the great South Channel... gale tonight. Gale Wednesday night. Gale possible Thursday into Thursday night. .Anz905...The great South Channel to the Hague line... gale tonight. Gale Wednesday night. Gale possible Thursday into Friday. .Anz910...East of the great South Channel and south of 39n... gale today into tonight. Gale Wednesday night. Gale possible Thursday into Friday. .Anz828...Inner waters from Cape Charles Light to Currituck Beach Light... gale possible Saturday night. .Anz925...Outer waters from Baltimore Canyon to Hatteras Canyon... gale possible Saturday night. .Anz830...Inner waters from Currituck Beach Light to Cape Hatteras... gale possible Saturday night. .Anz833...Inner waters from Cape Hatteras to Cape Fear... gale possible Saturday into Saturday night. .Anz930...Outer waters from Hatteras Canyon to Cape Fear... gale possible Saturday night. .Anz835...Inner waters from Cape Fear to 31n... gale possible Thursday night. Gale possible Friday night into Saturday night. .Anz935...Outer waters from Cape Fear to 31n... gale possible Thursday night. Gale possible Saturday into Saturday night.
.Forecaster musonda/Mills. Ocean prediction center.