Marine Weather for HS 100

Forecast

marine weather discussion for N Atlantic Ocean NWS ocean prediction center Washington DC 835 PM EDT Sat Apr 29 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 cold front approaching the New England and Long Island coasts from the NW, with a large high pres ridge extending W over the nt2 waters, and a robust pres gradient over the nrn and central nt2 waters between the cold front and the ridge. Latest available ascat hi-res and ascat passes from this morning show 20 to 25 kt winds in SW flow over the nrn and central nt2 zones, with mainly 10 to 20 kt winds indicated elsewhere in the offshore waters.

Models...the medium range models are in good overall agreement for tonight through Wed, so the representative GFS 10m/30m solution with the stability smart tool will be used for the wind grids for this timeframe. The models are showing timing differences for the Wed night through Thu night timeframe, with the ECMWF/UKMET models trending faster and the Gem/GFS models trending slower. Since the ECMWF was favored previously for Wed night through the rest of the forecast period, am planning to stay with it until a model consensus emerges. So will use a boosted version of the ECMWF for Wed night through the rest of the forecast period, in deference to the stronger Gem/GFS solutions. Confidence with the gale warnings for Mon night and Tue is considered to be average to good.

Seas...the wna wavewatch and ECMWF wam both initialized well over the coastal and offshore waters versus the latest observations. The models are in good overall agreement for tonight through Wed with only minor differences noted, so a 50/50 blend of the wna wavewatch and ECMWF wam will be used for the sea height grids for this timeframe. Then will use the ECMWF wam exclusively for Wed night through the rest of the forecast period, in order to be consistent with the ECMWF, which is the favored model solution for that period.

Extratropical storm surge guidance...N/A.

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

Over the short term, the new 12z models overall remain consistent and in reasonably good agreement. The models continue to share similar forecast timing for a cold front to push se across the nt1 waters tonight, become quasi-stationary across the nrn nt2 waters (near 38n) sun, then return slowly NNE across the nrn waters as a warm front Sun night into Mon night with a gradually strengthening associated sly gradient developing throughout much of the waters. Then with only slight timing differences, the 12z models forecast a cold front to move offshore late Sun night, then continue slowly se across the nt2 waters Mon into Mon night while gradually weakening. Similar to its previous respective runs, the 12z GFS/NAM/Gem remain consistent in forecasting the sswly gradient in advance of the cold front to strengthen to gale force Mon night into Tue across the nt2 waters primarily from the Gulf Stream swd. With the usually conservative 12z UKMET/ECMWF forecasting solid 25-30 kt boundary layer (bl) winds in this gradient, continue to have above average forecast confidence in these gales developing. Therefore plan on populating our forecast wind grids with the respresentative 12z GFS solution for tonight through Tue using our smart tool that will place stronger 12z GFS first sigma level winds in unstable areas and weaker 12z GFS 10m winds in stable areas (which will be over the majority of the waters). So per these winds do not anticipate making any significant timing and/or areal coverage changes to the previously forecasted gale warnings on Mon night/Tue.

In the long range, with minor timing differences, the 12z models all forecast a secondary cold front to sweep offshore Tue night/Wed with the 12z GFS remaining consistent in forecasting the strongest associated gradients (up to 25 or 30 kt). For now as a compromise will populate with a 50/50 blend of the 12z GFS first sigma/10m and 12z ECMWF bl winds on Tue night into Wed night. Then further out in the long range, the 12z global models continue to have timing differences in regards to the next developing surface low forecast to move towards the mid Atlantic coast Thu night. For now, with not a particularly high level of forecast confidence, will favor the more progressive 12z UKMET/ECMWF solutions versus the slower 12z GFS/Gem. Therefore will populate with all 12z ECMWF bl winds on late Wed night through Thu night.

Seas...other than being slightly too high across the nt1 waters, the 12z wavewatch iii and 12z ECMWF wam models have both initialized the current seas elsewhere equally well. With this in mind and since their associated 12z GFS and 12z ECMWF solutions are similar, will populate our forecast wave grids with a 50/50 blend of the 12z wavewatch iii and 12z ECMWF wam for tonight into Wed night. Then since the 12z ECMWF solution will become favored, will transition to populating with all 12z ECMWF wam seas late Wed night through Thu night.

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

.Warnings...Preliminary.

.Nt1 New England waters... None.

.Nt2 mid-Atlantic waters... .anz920...Baltimore Canyon to the great South Channel... gale possible Monday night into Tuesday. .Anz828...Inner waters from Cape Charles Light to Currituck Beach Light... gale possible Monday night into Tuesday. .Anz925...Outer waters from Baltimore Canyon to Hatteras Canyon... gale possible Monday night into Tuesday. .Anz830...Inner waters from Currituck Beach Light to Cape Hatteras... gale possible Monday night into Tuesday. .Anz833...Inner waters from Cape Hatteras to Cape Fear... gale possible Monday night into Tuesday. .Anz930...Outer waters from Hatteras Canyon to Cape Fear... gale possible Monday night into Tuesday.

$$

.Forecaster Scovil/vukits. Ocean prediction center.

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