Marine Weather for HS 100

Forecast

marine weather discussion for N Atlantic Ocean NWS ocean prediction center Washington DC 1004 PM EDT Fri Oct 19 2018

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

A cold front will move east across the waters and winds will increase ahead of the front with highest winds near the Gulf Stream in the short term. GOES 16 rgb geocolor satellite images show mostly clear over the waters but clouds are now entering the offshore waters and that is analyzed well on the current NCEP weather map. The last scatterometer pass was about 15z as described below in previous discussion but latest buoy and ship observations indicate 30 kt maximum winds. The latest NCEP weather map has high pressure just east of the central waters and it extends a weak ridge across most of the region. Inland frontal boundary near the Midwest states will approach the waters in the short term.

Seas are initially less than 6 ft over the region but will quickly build to over 6 ft with peaks around 12 ft by the issuance time. Nww3 and ecmwfwave have initialized well the observed seas pattern and both wave models agree well in the short term on swiftly building seas as the front approaches the waters. Unlike the winds, ecmwfwave will build the seas faster than nww3 over the northern waters. Since we are leaning toward ECMWF for winds will also use ecmwfwave for seas.

The latest run of models GFS/ukmethr/ecmwfhr/CMC have initialized well the latest synoptic surface observations with just minor differences on the actual position of the front inland that is moving east toward the waters and these differences increase in the short term. Models show enhanced winds near the Gulf Stream. GFS is rather fast and has storm force winds just east of the region while ecmwfhr though slower in moving the front than GFS, is weaker and does not show any storm force winds near the waters. For consistency and farther collaboration, will retain most of the official forecast winds and will stay with ECMWF in the extended period.

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

The latest NCEP surface analysis shows high pressure along the mid Atlc coast this afternoon, and a strong low pressure well E of the offshore waters. GOES visible satellite imagery shows cold cumulus streaming over the Atlc in the cold advection behind the front, though it is mainly E of the offshore waters with the main area of cold advection E of the region. Ascat overpasses from 14z and 15z this morning along with the latest surface observations show no more than 20 kt in the offshore waters, and the 12z GFS/ECMWF winds are initialized well when compared with the data. The models are in good agreement on the high moving E of the area tonight as a strong cold front currently in the Great Lakes region approaches the area from the NW. The 12z models then indicate that the winds will increase in the nrn zones in the southerly flow ahead of the front tonight into Sat as a strong low level jet sets up ahead of it with model 925 mb winds increasing up to 55 kt by Sat. The previous forecast had gales in the southerly flow over nt1, and at this time confidence is about average as the conditions seem marginal for sufficient mixing to bring sustained gales to the surface in nt1. However, the models also indicate lower static stability over nt2 as the front moves se while a low develops NE along the front. The 12z GFS/ECMWF/UKMET all show a stronger signal for higher winds developing in the unstable environment over the Gulf Stream, with winds reaching storm force in the far NE nt2 waters by Sat night for a brief period. The previous forecast had widespread sustained gales over the nrn waters with a small area of marginal storm force. This is supported by the 12z models, so planning on staying near the previous grids with this system as the guidance has been consistent with this solution.

The 12z models then indicate another strong cold front will move across the offshore waters Tue into Wed, with another round gales in the southerly flow ahead of the front. There are, however, some timing and intensity differences between the 12z global models with the ECMWF and GFS diverging the most from each other. The 12z ECMWF takes the associated surface low to the S of the GFS, and is about 12 hours slower with the front moving through the offshore waters. The 12z UKMET/Gem are somewhere in between with the timing, though closer to the ECMWF solution. The wpc medium range guidance is a compromise solution, and that seems reasonable given the differences. As a result, am planning on using the 12z ECMWF for the winds, but will time shift them 6 hours faster as a compromise. As far as the wind intensities are concerned, there is a somewhat strong signal in the guidance for sustained winds reaching gale force over nt2 for a brief period. Confidence is about average on the gales, so will continue previous headlines in the next forecast. Otherwise, will stay near the 12z ECMWF through the medium range.

Seas...the previous wave height grids are initialized well and are supported by the 12z wave guidance. Will be making some adjustments to them based on current data, but otherwise will be staying near the previous grids in the short range. Will then transition to the 12z ECMWF wam in the medium range to match up with the preferred winds from the 12z ECMWF, but will be time shifting the wave guidance 6 hours faster to account for the timeshift used with the winds.

.Extratropical storm surge guidance...No significant positive surge events appear likely over the region for the next few days.

.Warnings...Preliminary.

.Nt1 New England waters... .anz800...Gulf of Maine... gale possible Wednesday. .Anz805...Georges Bank west of 68w... gale tonight. Gale possible Wednesday. .Anz900...Georges Bank east of 68w... gale tonight into Saturday night. Gale possible Tuesday night. .Anz810...South of New England... gale tonight. .Anz815...South of Long Island... gale tonight. Gale Sunday.

.Nt2 mid-Atlantic waters... .anz820...Hudson Canyon to Baltimore Canyon... gale tonight. Gale Sunday. .Anz915...Hudson Canyon to the great South Channel... gale tonight into Saturday. Gale Sunday. .Anz920...Baltimore Canyon to the great South Channel... gale Saturday into Sunday. .Anz905...The great South Channel to the Hague line... gale tonight into Saturday. Storm Saturday night. Gale Sunday. Gale possible Tuesday night. .Anz910...East of the great South Channel and south of 39n... gale Saturday. Storm Saturday night. Gale Sunday. Gale possible Tuesday night. .Anz825...Inner waters from Baltimore Canyon to Cape Charles Light... gale Sunday. .Anz828...Inner waters from Cape Charles Light to Currituck Beach Light... gale Sunday. .Anz925...Outer waters from Baltimore Canyon to Hatteras Canyon... gale Saturday into Sunday. .Anz830...Inner waters from Currituck Beach Light to Cape Hatteras... gale Saturday. Gale Sunday. .Anz833...Inner waters from Cape Hatteras to Cape Fear... gale Saturday. Gale Sunday. .Anz930...Outer waters from Hatteras Canyon to Cape Fear... gale Saturday into Sunday.

$$

.Forecaster musonda/Kells. Ocean prediction center.

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