marine weather discussion for N Atlantic Ocean NWS ocean prediction center Washington DC 1013 am EDT Thu Mar 21 2019
.Forecast discussion...Major features/winds/seas/significant .Weather for the North Atlantic ocean W of 50w from 30n to 50n.
The GOES visible satellite imagery shows an area of developing low pressure just inland over North Carolina, along with a cold front extending to the se and S from the low over the srn offshore waters. The lightning density product along with the satellite imagery indicate showers and tstms along the boundary near the Gulf Stream. The models indicate conditions will be conducive for convective activity over the warmer SSTs, so planning on keeping mention of scattered showers and tstms in the update package. Otherwise, the ascat wind retrievals from 01z last night indicated up to 30 kt ahead of the frontal boundary, though current surface reports only indicate up to 25 kt along the coast. However, the GFS and ECMWF winds indicate all of the observations are not in the areas where the highest winds were expected at 12z, and both indicate 30 kt increasing later today as the low moves slowly while strengthening. The models are now in fairly good agreement on the track and development of this system, so confidence in the previous gale headlines is above average since there is a strong signal in the guidance for them. As a result, will only be making minor adjustments to the wind and hazard grids with this system, which maintains gales in the offshore waters into Sat night.
The models then start diverging late sun into Mon with the next frontal system moving off the New England coast. There has been some slight timing differences on the front, with the GFS/ECMWF in relatively decent agreement. However, the models then diverge on the development of a low along the front, with the GFS stronger with the NE flow to the N of the low near the Gulf Stream. As such, the GFS increases winds to gale force in nt2, and is much stronger than the rest of the 00z guidance. As a result, confidence is relatively low in the gales since there is not support. The previous forecast stayed near the ECMWF and kept winds below gale force through the medium range period, so planning on staying along those lines in the update package.
----------------------------------------------------------------- Previous discussion...
High pressure just northeast of the region will continue to move farther east of the waters and low pressure will develop over the far southwestern waters then move north inland near the coast from North Carolina through the mid Atlantic states to New England in the short term. High pressure will then build into the southern waters from the south and west of the waters before moving east of the southern waters in the extended period. Another low pressure will approach the waters form the west toward the end of the forecast period. Currently, GOES east geocolor satellite images show few clouds over the northern waters while most of the clouds with cold tops are just east of the region. The images also show weak cyclonic circulation over the far southwestern waters. NCEP weather map has low pressure 1013 mb over waters adjacent to the Carolinas with a warm front stretching northeast across the central waters and a cold front stretches southwest across the far southern waters. Pressure gradient is well relaxed across the waters while maximum winds to 30 kt are near the low pressure mentioned above.
Models have generally continued to agree on moving low pressure, over the southern waters, north but they still differ on the actual path. GFS and ecmwfhr still have the low moving inland across the mid Atlantic states into New England while CMC has it passing across the waters and ukmethr lies in between but mainly along the coast. While GFS and ecmwfhr have similar path, they differ on wind speed as surface winds for ecmwfhr do not reach gale force threshold and so will continue with GFS for winds and will retain the warning headlines.
.Seas...Are relatively large over the southern waters with a peak at 15 ft over the far southeastern waters. Otherwise seas range between 6 and 13 ft over the waters south of the Gulf Stream and they range between 3 and 6 ft north of the Gulf Stream. Nww3 fits very well the observed seas pattern and has been quite consistent in the last previous run. Ecmwfwave is also close to the observed seas and agree well with nww3 in the short term on keeping relatively large seas over the southern waters and will then spread north. Otherwise, will keep ecmwfwave seas in the forecast.
.Extratropical storm surge guidance...Estofs values are more reasonable than the etss with the surge moving up the coast over the next few days with the strong easterly fetch ahead of the aforementioned developing coastal low. Values are just above 1 ft in the estofs, which seem reasonable considering the intensity of the winds. Consult your local National Weather Service office for more detailed information.
.Nt1 New England waters... .anz800...Gulf of Maine... gale tonight into Friday night. Gale possible Saturday. .Anz805...Georges Bank west of 68w... gale tonight into Friday night. Gale possible Saturday into Saturday night. .Anz900...Georges Bank east of 68w... gale tonight into Friday night. Gale possible Saturday into Saturday night. .Anz810...South of New England... gale Friday into Friday night. Gale possible Saturday into Saturday night. .Anz815...South of Long Island... gale Friday night. Gale possible Saturday into Saturday night.
.Nt2 mid-Atlantic waters... .anz820...Hudson Canyon to Baltimore Canyon... gale Friday into Friday night. Gale possible Saturday into Saturday night. .Anz915...Hudson Canyon to the great South Channel... gale Friday into Friday night. Gale possible Saturday into Saturday night. .Anz920...Baltimore Canyon to the great South Channel... gale today into Friday night. Gale possible Saturday into Saturday night. .Anz905...The great South Channel to the Hague line... gale tonight into Friday night. Gale possible Saturday into Saturday night. .Anz910...East of the great South Channel and south of 39n... gale tonight into Friday night. Gale possible Saturday into Saturday night. .Anz825...Inner waters from Baltimore Canyon to Cape Charles Light... gale Friday night. Gale possible Saturday. .Anz828...Inner waters from Cape Charles Light to Currituck Beach Light... gale today. Gale Friday night. .Anz925...Outer waters from Baltimore Canyon to Hatteras Canyon... gale today. Gale Friday into Friday night. Gale possible Saturday. .Anz830...Inner waters from Currituck Beach Light to Cape Hatteras... gale today. Gale Friday night. .Anz930...Outer waters from Hatteras Canyon to Cape Fear... gale today into Friday night. .Anz935...Outer waters from Cape Fear to 31n... gale tonight.
.Forecaster Kells/musonda. Ocean prediction center.