marine weather discussion for N Atlantic Ocean NWS ocean prediction center Washington DC 950 am EDT Mon 20 Aug 2018
.Forecast discussion...Major features/winds/seas/significant .Weather for the North Atlantic ocean W of 50w from 30n to 50n.
The latest GOES-16 satellite imagery, lightning data, and cam guidance suggest that there are likely at least marginal gale force winds associated with the widespread thunderstorms across the mid Atlantic offshore waters from Baltimore Canyon to Cape Fear in the vicinity of the stationary front. Therefore, we will continue to explicitly mention these winds in thunderstorms across these inner and outer offshore zones through the afternoon. The models then were generally consistent with the stationary front lifting north across the northern nt2 and nt1 zones as a warm front Tue into Wed, and a cold front expected to move east across the offshore waters Wed evening through Thu night. It still appears that the gales forecast across the northern outer nt2 waters Wed into Wed night are a strong possibility. We will not be making any adjustments to the timing or areas of these warnings, and other than some slight adjustments to the near term wind grids, the grids will remain mostly consistent in this mornings forecast updates.
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For today into early Wed, the 00z models are all in very good agreement over the offshore waters. We will populate grids with the very consistent 00z NAM-nested throughout this short term period as it matches up well with current conditions, and an ascat overpass from last evening around 0207z which indicated moderate E and NE winds up to 20 to 25 kt occurring over most of the New England offshore waters, and SW winds up to 20 kt S of the cold front over southern into central nt2 waters, off the se and southern mid-Atlantic coasts. The cold front is still forecast to stall off the NE N. Carolina coast today into tonight with weak low pressure areas tracking E along the frontal boundary. The front will then lift back N as a warm front Tue and Tue night as low pressure tracks NE from the Great Lakes. One of the main concerns over the next couple of days will continue to be the threat for very gusty winds, potentially exceeding gale force, and very rough seas in and near thunder- storms over the waters. The latest GOES-IR imagery and lightning density data show the stronger thunderstorms near and to the S of the cold front extending from the southern Delmarva and N. Carolina coasts E and NE over central into northern nt2 waters, with a few thunderstorms scattered over southern nt2 waters as well. Forecast confidence levels are above average into early Wed over the offshore waters, with no hazard-level winds expected outside of the stronger thunderstorms.
Over the medium range, Wed into Fri night, the 00z models appear to be coming into better agreement regarding the timing of the cold front forecast to pass E and se over the waters Wed into early Thu. We will continue to populate with the 00z NAM guidance which has good support from the 00z GFS, 00z UKMET, 00z Canadian Gem and 00z ECMWF for Wed into early Thu over the waters. This will result in adding gales to the outer nt2 waters, or zones anz920-910-905 for Wed into Wed night. Current SSTs are above average over most of the mid-Atlantic and New England waters, which will also help support these stronger winds being added to the offshore waters forecast. Additional minor adjustments to these stronger winds could occur over the next day or two. Please closely monitor the latest opc forecast. For later Thu through Fri night we will then populate the forecast with consistent 00z ECMWF, which has changed little from previous cycles. Therefore, the cold front is expected to reach the S. Carolina or Georgia coasts by later Thu or Thu night, and then stall, with high pressure building E over most of the eastern U.S. The high will then slowly build offshore later Thu night into Fri night as the front slowly weakens over the southern nt2 waters. Confidence levels are slightly above average over the medium range.
Seas...sea heights over the offshore waters early this morning are running very close to the previous opc forecast grids, with sea heights ranging from 6-7 feet just off the Jersey Shore, to 8 feet over waters well off the Virginia and N. Carolina coasts, to 3 to 5 feet or so off the se U.S. Coast. For the early morning package, we will remain close to the previous grids today into tonight, with some edits in deference to nearby coastal WFO and TAFB grids. For Tue into early Fri, we will use a 80 percent 00z wavewatch, 20 percent 00z ECMWF wam blend, and continue to add up to 10 percent in and near the gale force wind areas Wed into Wed night. For most of Fri and Fri night we will use a 50/50 blend of the wavewatch and wam models.
.Extratropical storm surge guidance...The 00z etss and estofs models continue to provide for surge values around a half-foot or slightly higher in vicinity of the New Jersey and northern Delaware coasts today into Tue. Otherwise, no significant surge is expected. Monitor the latest forecasts from coastal National Weather Service offices for details.
.Nt1 New England waters... None.
.Nt2 mid-Atlantic waters... .anz920...Baltimore Canyon to the great South Channel... gale possible Wednesday. .Anz905...The great South Channel to the Hague line... gale possible Wednesday into Wednesday night. .Anz910...East of the great South Channel and south of 39n... gale possible Wednesday.
.Forecaster Clark/Mills. Ocean prediction center.