Marine Weather for HS 100


marine weather discussion for N Atlantic Ocean NWS ocean prediction center Washington DC 828 PM EDT Thu Mar 23 2017

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

Update...the 18z NCEP surface analysis shows a large high pres ridge moving E over all of the coastal/offshore waters, and a strong 994 mb low centered over srn Newfoundland. Latest available ascat hi-res and ascat passes from this morning show 25 to 35 kt winds in NW flow over the Georges Bank zones and the NE part of the nt2 waters in the tight pres gradient between the low and the ridge, and 20 to 25 kt winds in NE flow across the SW part of the nt2 area.

Models...the medium range models are in good overall agreement across the offshore waters for tonight into Fri, so the GFS 10m solution will be used for the wind grids over this timeframe. The GFS continues to look overdone with the strength of the SW flow over the nt1 and nrn nt2 waters for later Fri and Fri night, and the GFS is also faster than most of the other models for Mon and Mon night. Thus, the more representative ECMWF will be used for later Fri through Mon night. The models are in poor agreement regarding the timing and trajectory of a low which is expected to move off the mid Atlantic coast Tue into Tue night, but since the GFS looks like the best median model solution, it will be used for Tue through the rest of the forecast period.

Seas...the wna wavewatch initialized 2 to 4 feet too low over the Gulf of Maine and Georges Bank waters, so the more robust ECMWF wam is preferred for tonight. The wavewatch/wam are in decent agreement over the offshore waters for Fri through Mon night with only minor differences noted, so a 50/50 blend of these models will be used for the sea height grids during that timeframe. A somewhat modified/capped wna wavewatch will be used exclusively for Tue through the rest of the forecast period, in order to be consistent with the preferred GFS model.

Extratropical storm surge guidance...N/A.

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

There was an ascat pass at about 1445z with a swath across the far ern waters of Georges Bank and into the far ern waters of the nrn mid Atlantic waters. Winds were at bit stronger than grid values in this region with 35 kt while we had 30 kt in this area. There was a ship observation just W of this area which had 25 kt although could not find any qc history with this observation. In any case the area of gales should have moved E of the waters several hours ago.

In the early afternoon at 18z high pressure was centered over the Delmarva Peninsula and will be moving E into the offshore waters through tonight and Friday. The center of high pressure moves E of the offshore waters by Friday afternoon while becoming weaker. With regards to winds over the offshore waters winds become light at 15 kt or less throughout most of the region by 8 am Friday. By late Friday a warm front will move NE towards the wrn New England waters. Gem/UKMET/GFS are consistent with having winds to 30 kt by late Friday with the approaching warm front. Models are consistent with low pressure developing N of the New England waters Friday night and strengthening while passing E of the waters. Associated cold front moves S over the New England waters late Friday night into Saturday...then crossing into the nrn mid Atlantic waters later on Saturday before stalling over the nrn mid Atlantic through about Sunday night. Models are similar with high pressure building in from the NW over the New England waters late Saturday into Saturday night...then settling across the area Sunday...before passing E of the New England waters Sunday night and Monday. By Monday an upper shortwave will move across the PA/NY state and then E into the offshore waters late Monday and Monday night while becoming weaker. As this occurs the stalled front moves back to the N over the New England waters with weak low pressure dissipating as it moves E into the waters by early Tuesday. By late Tuesday and Tuesday night models diverge with low pressure that approaches and crosses into the waters. Prefer the GFS which is slower than the ECMWF with moving the low pressure into the waters. There is some agreement from the UKMET on a slower solution. Also the weather prediction center has accepted the idea of the slower progress of low pressure moving E into the waters.

For the grids plan to favor the GFS initially through early Friday...then use the ECMWF through about Monday night...then use GFS from early Tuesday into Tuesday night. The GFS seems overly strong with Ely winds by late Tuesday and Tuesday night over the New England waters...and will limits winds since no other guidance is as strong with winds over the nrn New England waters.

Seas...for seas earlier observations from 14 and 15z just along and E of the New England waters showed 17 ft with buoy 44011 and 20 ft with buoy 44024. These observations were much better depicted by the ECMWF wam over the . Over Georges Bank the ECMWF wam matched with the ECMWF wam...but was about 3 to 4 ft lower just E of the New England waters with the 20 ft seas. By comparison the wwiii was about 4 ft too low with 44011 and about 8 ft too low with buoy 44024. Will use the ECMWF wam across the offshore for tonight....then use a 50/50 blend of the wwiii and ECMWF wam from Friday into Monday...then use the wwiii although will cut seas down by late Tuesday with seas seeming too high over the New England waters.

.Extratropical storm surge guidance...N/A.


.Nt1 New England waters... None.

.Nt2 mid-Atlantic waters... None.


.Forecaster Scovil/Rowland. Ocean prediction center.

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