Marine Weather for HS 100


marine weather discussion for N Atlantic Ocean NWS ocean prediction center Washington DC 743 am EST Mon Dec 10 2018

.Forecast discussion...Major features/winds/seas/significant .Weather for the North Atlantic ocean W of 50w from 30n to 50n.

Low pressure located about 120 nm E-se of Cape Hatteras early this morning is continuing to produce widespread gales over most of the central and southern nt2 waters. This low will track E today and pass E of the waters this evening. A second low is still forecast to develop along a frontal boundary trailing W and SW from the first low, over the se nt2 waters near 32n 74w around or after midnight tonight. This second low will intensify over se nt2 waters Tue morning, before shifting E of these waters Tue afternoon. Storm force winds appear likely just to the W and SW of this second intensifying low Tue into Tue night. For the morning update, we will make only minor adjustments to the ongoing forecast/grids especially closer to TAFB and the coastal WFO waters in deference to their grids/forecasts. No change to the previous hazards will be made for the morning update as well.

Note: some possible delay in our products is possible today as opc upgrades our server later this morning.

Seas...sea heights range from around 21 ft E of Cape Hatteras to 3 to 5 ft over northern nt1 or the northern New England waters according to the latest observations. Little change appears needed to the ongoing forecast for the mid-late morning update. Some adjustments will be made in deference to nearby coastal WFO and TAFB grids over the next few days.

----------------------------------------------------------------- Previous discussion...

The latest NCEP surface analysis and current surface observations show a developing low pressure system across the nt2 offshore waters this morning, and the northerly direction in the winds along the coast indicates the low center to the E of Cape Hatteras. The analysis also indicates that the pressure gradient has tightened between the strengthening low and a high pressure ridge to the NE, with strong easterly flow over the Gulf Stream across central and northern nt2. The current reports indicate winds to gale force to the E and N of the low with buoy 44014 in nt2 gusting to storm force. However, none are in the vicinity of where the 00z GFS/ECMWF showed the highest winds which are indicated in zones to the W of the nrn Outer Banks, mainly in the outer waters over the Gulf Stream. The previous forecast had storm force winds over several of the central nt2 offshore zones, and this seems reasonable when considering the deep mixing indicated by the convective activity in the GOES infrared satellite imagery and the lightning density product which shows the front acting as a focus for convection mainly in the unstable environment over the Gulf Stream. However, with the low moving away from the coast, the models indicate that the winds will briefly drop just below storm force today. Confidence remains high on the storm force winds for 06z this morning as a result of the strong satellite signature, and is also high with the large area of surrounding gales which covers a large portion of nt2. The 00z models are in fairly good agreement on the track and intensity of the low over the next 12 hours, before the 00z GFS diverges from the rest of the guidance on the track and handling of the low center. The 00z ECMWF and UKMET indicate the low will move quickly off the E today in response to a quickly moving shortwave trough passing through area coincident with the right entrance region of a strong upper level jet streak moving quickly to the E. The models then indicate a second low forming over nt2 today and moving slowly E across central nt2 as another shortwaves slides offshore, then shows the low passing E of the offshore waters by Tue night. The GFS has been very inconsistent with the development of the aforementioned features, and takes the second low to the S of the 00z model consensus. The 00z ECMWF is supported a bit better by the rest of the 00z guidance, and shows strong development as the low moves slowly across the Gulf Stream Tue into Tue night while bring the winds back up to storm force in the outer waters. This is supported by the 00z UKMET/Gem solutions, and is close to continuity, so planning on starting out with the 00z ECMWF in the next forecast while boosting the normally conservative winds by 15 percent over the Gulf Stream to account for the deeper mixing.

The 00z models then remain in fairly good agreement Wed with a ridge moving across the waters, before a weaker shortwave tough moves across the nrn zones late Thu. There are some differences on the intensity of the trough, though all solutions show a fairly weak surface reflection. The models then indicate a stronger system approaching the coast from the W on Fri, and there is a fair amount of model spread in the 00z guidance. The 00z ECMWF trended slower from its previous run, and is now where it was in last night's 00z run. It is in somewhat decent agreement with the 00z UKMET, and the 00z GFS is faster than the rest of the guidance while N of the ECMWF solution. The 00z Gem is much further N, and is an outlier solution. The 00z gefs members have a slightly stronger signal for a slower solution, as does the wpc medium range guidance. However, since there is quite a bit of uncertainty in the guidance, confidence is fairly low in any one solution. As a result, am planning on staying near the 00z ECMWF through the medium range period as it maintains continuity fairly well, and has slightly more support than the rest of the 00z guidance. Am also planning on continuing previous gales headlines for late Fri as all of the models indicate strong southerly flow ahead of the associated surface front as it moves into the unstable environment over nt2.

.Seas...The 00z ECMWF wam is initialized within a ft of the current observational data in the offshore waters this morning, including off the nrn Outer Banks where buoy 44086 reported 21 ft at 06z. The model seems representative considering the track and intensity of the low currently off the coast, and matches well with the preferred 00z ECMWF solution through the period. As a result, am planning on using the 00z ECMWF wam in the next forecast.

.Extratropical storm surge guidance...In the strong easterly fetch off the srn mid Atlc coast this morning, the 00z estofs and etss both show a positive surge along the coast from Cape Hatteras to Cape May with highest values near 1.5 ft along the Outer Banks into this afternoon. This seems reasonable considering the strong flow, though might be a tad underdone. The models then show another surge of about a foot on Fri in the strong southerly flow ahead of the second strong low pressure system. However, since the GFS was deemed a bit too fast, the surge is more than likely too fast to come as well. Interests along the mid-Atlantic and southeast U.S. Coasts should monitor the latest advisories or warnings, and forecasts from coastal National Weather Service offices.


.Nt1 New England waters... None.

.Nt2 mid-Atlantic waters... .anz920...Baltimore Canyon to the great South Channel... gale today. Gale Tuesday. Gale possible Wednesday. .Anz905...The great South Channel to the Hague line... gale Tuesday night. Gale possible Wednesday into Wednesday night. Gale possible Friday night. .Anz910...East of the great South Channel and south of 39n... gale Tuesday into Tuesday night. Gale possible Wednesday into Wednesday night. .Anz825...Inner waters from Baltimore Canyon to Cape Charles Light... gale today. .Anz828...Inner waters from Cape Charles Light to Currituck Beach Light... gale today. .Anz925...Outer waters from Baltimore Canyon to Hatteras Canyon... gale today into Tuesday night. Gale possible Wednesday. .Anz830...Inner waters from Currituck Beach Light to Cape Hatteras... gale today into tonight. Gale possible Friday night. .Anz833...Inner waters from Cape Hatteras to Cape Fear... gale today into tonight. Gale possible Friday night. .Anz930...Outer waters from Hatteras Canyon to Cape Fear... gale today into tonight. Storm Tuesday. Gale possible Friday night. .Anz835...Inner waters from Cape Fear to 31n... gale today into tonight. Gale possible Friday night. .Anz935...Outer waters from Cape Fear to 31n... gale today into Tuesday. Gale possible Friday night.


.Forecaster Mills/Kells. Ocean prediction center.

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