AGNT40 KWNM 050140 MIMATN Marine Weather Discussion for N Atlantic Ocean NWS Ocean Prediction Center Washington DC 840 PM EST Thu Mar 4 2021 .FORECAST DISCUSSION...Major features/winds/seas/significant .weather for the North Atlantic Ocean W of 50W from 30N to 50N. The latest buoy and ship observations show winds gusting to gale force and slightly above along and off the coast of Maine and Massachusetts, with the 00Z preliminary OPC-NCEP surface analysis indicating a low pressure trough moving SE over the Gulf of Maine and a cold front extending from just S of Cape Hatteras, east and northeastward across the central NT2 waters this evening. Based on the latest observations and guidance we see no need to make major changes to the ongoing OPC forecast for the evening update, with gales over the Gulf of Maine and Georges Bank slowly diminishing by midnight or after, and then developing further to the SW and S off the southern New England and Mid- Atlantic coast, and the north wall of the Gulf Stream as indicated earlier with strong cold air advection. These gales will then likely slowly diminish later Fri and Fri night as the pressure gradient and advection over this region begins to slowly weaken. For the evening update, a few minor edits will be made mainly for initial conditions and in deference to nearby coastal WFO and TAFB grids over the next few days. Seas...Significant wave heights range from 10 ft or so over the eastern Gulf of Maine waters to 3 ft or so over the far western part of the inner waters, from the Delmarva southward according to the latest obervations and 00Z RA1 OPC sea state analysis. No major changes appear needed for the evening update, although we will add around a foot or so to the grids over portions of the New England waters this evening based on the latest observations. A few manual edits will also be made over the next few days in deference to nearby coastal WFO and TAFB grids. ----------------------------------------------------------------- PREVIOUS DISCUSSION... Cold air advection continues to increase in the wake of a cold front clearing E of the northern and central waters this afternoon, with buoys along the northern Mid-Atlantic and New England coasts reporting sustained 8-min winds into the mid and upper 20s, with several stations gusting at or above gale force. Overall the forecast remains consistent for the next forecast cycle; gales are likely to begin around 00z this evening closer to the coastal areas, then spread more to the outer zones and atop the Gulf Stream by later tonight into Fri. With SSTs still running upwards of +5C, and with prior events significantly over-performing compared to model guidance, we continue to have above average confidence in gales, despite the marginal signal in the guidance. Will update the near term grids blending the latest wind-bias corrected 12z ECMWF into the ongoing forecast, adjusting for the Gulf Stream influences. Modest NW flow continues into the weekend as a series of weaker low pressure troughs move across the waters. 12z models agree a southern stream low likely develops S of the area Sat, passes S of the waters Sat night, then intensifies NE into the open ocean Sun and Sun night as a strong high builds to the Eastern Seaboard. The preferred 12z ECMWF trended a little more robust with the wind field in the increasing pressure gradient, suggesting gales are possible later Sun and Sun night across the outer portions of the southern waters, particularly again atop the Gulf Stream. But that said the ECMWF is considerably on the stronger side of guidance envelope, including even the Canadian and higher first sigma winds from the GFS. Will continue to lean toward this higher end ECMWF guidance through the weekend, and with no support in the other models yet, limit winds to 32 kt and below gale for now. Bears watching. High pressure then settles offshore Mon through Tue night, as a couple of weak fronts move across the northern portions. Winds look to remain well below hazard criteria here. Will trend the forecast from 12z ECMWF toward the NBM output for the end of the medium range. Seas: With the wind grid preference closest to the 12z ECMWF, will base the significant wave heights on the 12z WAM in the upcoming forecast package. Will continue to increase seas in strong NW flow in the near term, adjusting both for the Gulf Stream and hazard level winds, ultimately increasing the seas into the 12 to 16 ft range (about 33 percent above guidance). Otherwise, will lean close to the WAM for the remainder of the grids, and then trend toward a multi-cycle and multi-model blend at the end of the medium range where the NBM was preferred. Extratropical Storm Surge Guidance: No significant positive surge events are expected during the next several days. Please monitor products from coastal National Weather Service offices for detailed water level information. .WARNINGS...Preliminary. .NT1 New England Waters... .ANZ800...Gulf of Maine... Gale tonight. .ANZ805...Georges Bank west of 68W... Gale tonight. .ANZ810...South of New England... Gale tonight. .ANZ815...South of Long Island... Gale tonight. .NT2 Mid-Atlantic Waters... .ANZ820...Hudson Canyon to Baltimore Canyon... Gale tonight. .ANZ915...Hudson Canyon to the Great South Channel... Gale tonight. .ANZ920...Baltimore Canyon to the Great South Channel... Gale tonight into Friday. .ANZ905...The Great South Channel to the Hague Line... Gale Friday. .ANZ910...East of the Great South Channel and south of 39N... Gale tonight into Friday. $$ NOTICE TO CUSTOMERS: Public comments are being accepted until March 12, 2021 on a proposal to discontinue this Marine Weather Discussion (MIM) text product. More information, including how to submit feedback, can be found at https://www.weather.gov/media/notification/pns21-09opc_mim.pdf /all lower case letters/ .Forecaster Mills/Collins. Ocean Prediction Center.