AGNT40 KWNM 200736 MIMATN Marine Weather Discussion for N Atlantic Ocean NWS Ocean Prediction Center Washington DC 336 AM EDT Sat Jul 20 2019 .FORECAST DISCUSSION...Major features/winds/seas/significant .weather for the North Atlantic Ocean W of 50W from 30N to 50N. Over the short term, the 00Z guidance has remained quite consistent, and in very good agreement over the region. An ASCAT overpass from last evening around 0224Z indicated W and SW winds up to 20 kt over the offshore waters. The 00Z NAMNest matched these winds quite well, and we will populate grids with the 00Z NAMNest for today into tonight, will little change from the past few OPC forecasts, as W to SW winds prevail into tonight, with a developing coastal low pressure trough and high pressure ridge along 30N or so dominating conditions into tonight. The latest radar, GOES-IR satellite imagery, and lightning density data all indicate a few isolated to scattered thunderstorms occurring near the N wall of the gulf stream, extending from just off the NE coast of North Carolina E and NE to near 37N 68W, with a few thunderstorms also off the Georgia and southern South Carolina coasts. The latest SREF thunderstorm guidance continues to show the highest chance for thunderstorms, mainly isolated to occasionally scattered in nature, over the central and southern NT2 waters into tonight, with more widespread thunderstorm activity possible later Sun through Mon as a cold front moves into the area. Caution is advised for locally very strong gusty winds, possibly near gale force or higher, and very rough seas in and near any of the heavier thunderstorms. For later tonight through Mon, we will trend the forecast toward the very consistent 00Z ECMWF winds and add up to 10 percent to these winds mainly near the north wall of the gulf stream. This will result in little change from the past few OPC forecasts for the early morning package, with a cold front moving toward the coast later Sun, then passing SE over the NT1, or New England, waters Sun night, and stalling over the New England waters Mon as low pressure develops along the front over New Jersey by 00Z Tue. Gales do not appear likely over the short term part of the forecast, with the main concern continuing to be the locally very strong winds and very rough seas in and near any of the heavier thunderstorms through Mon. Forecast confidence is above average over the short term. Over the medium range, Mon night through Wed night, we will continue to rely on something closest to the 00Z ECMWF guidance and adjust winds upward by 10 percent or so near the north wall of the gulf stream. The 00Z ECMWF is nearly identical to the 12Z cycle, with the ECMWF having good support from the 00Z GFS and 00Z Canadian GEM. We still expect low pressure to move from New Jersey early Mon night to coastal Maine late Mon night, and then cross Nova Scotia during Tue with the trailing cold front moving S and SE over New England and the inner portion of the Mid- Atlantic offshore waters later Tue, with the front slowing as it reaches a line from the NE NT2 waters southwestward to South Carolina coast by later Wed and Wed night, with the potential for weak low pressure forming along the front off the Carolina coast Wed night as high pressure builds E over the Mid-Atlantic states and into New England. At this time, we will not add any gales to the offshore forecast, with widespread winds to 30 kt likely Mon night into Wed, mainly ahead of the cold front and near the low pressure area moving NE over the New England waters. Additional adjustments to the OPC forecast are likely over the next few days. Please closely monitor the latest forecast. Overall, the forecast confidence levels remain above average over the medium range, except below average for any gales occurring over the waters. Caution is still advised over the medium range for the potential for heavy thunderstorms especially near the low pressure area and cold front crossing the waters, with very gusty winds and very rough seas in or near any thunderstorms. .Seas: The previous OPC gridded sea heights, 00Z ECMWF WAM and 00Z Wavewatch guidance are all quite similar across the region early this morning, with the 00Z ECMWF WAM very similar to the 12Z cycle which was used for the previous few forecasts. For the early morning package we will use a 75 percent 00Z WAM, 25 percent previous grid blend, and boost sea heights up to 10-15 percent near the N and W walls of the gulf stream into next week across the area. This should adjust to match the wind forecast over the waters during the next few days with no significant changes from the past few OPC forecasts. Extratropical Storm Surge Guidance: No significant positive surge events are expected during the next few days. .WARNINGS...Preliminary. .NT1 New England Waters... None. .NT2 Mid-Atlantic Waters... None. $$ .Forecaster Mills. Ocean Prediction Center.