marine weather discussion for N Atlantic Ocean NWS ocean prediction center Washington DC 857 am EDT Thu Apr 26 2018
.Forecast discussion...Major features/winds/seas/significant .Weather for the North Atlantic ocean W of 50w from 30n to 50n.
The 12z surface analysis indicated occluded/cold front over the far southeast New England offshore waters and far northeast mid Atlantic waters, with a secondary cold front over the western waters. Satellite imagery and lightning data indicate thunderstorms over far eastern Georges Bank zone, as well as the northeast nt2 zones just ahead of front. Overall, the current wind grids continue to look on track and do not plan on making any major changes with the morning update. Will also leave existing warning headlines which keep gales in above mentioned zones into the early afternoon before decreasing later in the afternoon. The 12z sea state analysis indicated that the observed seas matched up well with the ECMWF wam values, and also do no plan on making any changes to the wave grids.
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Over the short term, an evening ascat overpass from around 0210z indicated gales occurring over NE nt2 waters, or similar to the ongoing forecast. For the short term, we will populate grids with an even blend of the old grids, and 00z high resolution warw as the warw appears to be initializing quite well over the region early this morning. We will make a few manual edits in deference to the previous hazards and nearby coastal WFO and TAFB grids. Overall, this blend will result in little change over the waters today through Fri from the previous opc forecast. Gales occurring ahead of a cold front moving E over the region will likely push E of the waters by later this morning, or early afternoon at the latest. Low pressure near Long Island at 06z has a cold front extending S over the waters and a warm front extending se over the outer nt2 waters. IR satellite imagery and lightning data indicate scattered thunderstorms occurring near and just E of the cold front over the outer nt2 waters. The thunderstorms may produce winds in excess of gale force for a time as they track E and NE over NE nt2 and possibly near Georges banks or the se nt1 offshore waters this morning, with the activity shifting E of the waters this afternoon. The next low pressure system is expected to then move from the Gulf states to the Carolinas tonight, reach the Delmarva coast by midday Fri, and southern New England or around Long Island Fri evening. For now, we will keep winds sub-gale with this system with any gale force winds likely limited to the vicinity of thunderstorms that develop near and E of the low tonight through Fri. Confidence in the forecast for today into Fri is above average.
For the medium range, Fri night through Mon night, the 00z global models are in pretty good agreement over the region. We will populate the grids with a 50/50 blend of the previous grids and 00z ECMWF guidance as it has remained quite consistent from the 12z cycle which was used for the previous forecast. This will also result in little change from the previous opc forecast for the early morning package. We still expect the low near Long Island Fri evening to move to near the Maine coast later Fri night, and then to New Brunswick, Canada on Sat. A series of cold fronts will then move E and se over the waters Sat into Sun night. The 00z ECMWF wants to now develop more of a low on one of these fronts as it crosses the waters Sat night. It appears as if the low will remain weak, and we will keep winds below gale force over the region throughout the medium range portion of the forecast, or similar to the past few opc forecasts. A large high pressure area will slowly build over the eastern U.S. Sun into Sun night, and then expand E off the se coast Mon and Mon night. Overall, confidence over the medium range portion of the forecast is slightly above average.
Seas...as has been the case over the past couple of days, the latest ECMWF wam guidance seems to be more in line with latest observations, and also in line with an earlier altimeter pass over the waters, with the 00z wavewatch initially too low over especially waters off the southern New England and mid-Atlantic coasts. We will, therefore, remain close to the 00z ECMWF wam guidance over the waters today into early next week. Per the 06z ra1 opc sea state analysis, sea heights range from near 22 feet over the outer northern nt2 waters near 38n 69w, to 6 feet or less off the se U.S. Coast.
.Extratropical storm surge guidance...The 00z estofs guidance continues to show values slightly higher than the etss guidance near the mid-Atlantic and New England coasts today. These slightly higher values appear reasonable for today, with improving conditions likely by tonight. A weak low moving up the coast later tonight into Fri night may produce some minor surge issues, and we see no need to deviate too much from the latest estofs guidance over region into the weekend. Please monitor the latest information from local coastal National Weather Service offices for details.
.Nt1 New England waters... .anz900...Georges Bank east of 68w... gale today.
.Nt2 mid-Atlantic waters... .anz905...the great South Channel to the Hague line... gale today.
.Forecaster kosier/Mills. Ocean prediction center.