marine weather discussion for N Atlantic Ocean NWS ocean prediction center Washington DC 333 PM EST Thu Dec 14 2017
.Forecast discussion...Major features/winds/seas/significant .Weather for the North Atlantic ocean W of 50w from 30n to 50n.
Surface low analyzed near 40n66w 995 mb at 18z per opc surface map, and associated storm force winds will have cleared just south and east of the opc offshore zones by next forecast issuance. Will allow storm headlines to expire accordingly. Based on recent ascat overpasses late morning, higher first sigma layer winds from the GFS continued to initialize well in strength and areal coverage of associated wind field.
Fri into Sun: surface low forms off the N Carolina coast during the day Fri, then rapidly intensifies NE pulling a strong cold front across the offshores. 12z models have shifted low track ever so slightly to the north, but enough of a shift to indicate a real possibility of storm force winds clipping the outer zones 910 and 905. This setup is very similar to the event from today: 925 mb winds 50-60 kt range atop the Gulf Stream. Since this is the first set of guidance that has shifted these winds into opc waters, feel it best to ensure the trend continues before adding storm headlines into the grids. After the low clears the waters another round of seasonal, cold air advection gales in the forecast beginning Fri night across the southern and central zones, with axis of strongest winds then shifting to the northern waters Sat and Sat night. Gales gradually abate below warning criteria late Sat night, ending west to east as the parent low pressure gains longitude well away from the region. Opc has been using the GFS during this time frame for a few shifts, and see no reason to deviate now. Will be using a smart tool that uses higher first sigma layer winds in unstable conditions and 10m winds elsewhere.
Sun night onwards: amplified upper pattern transitions towards a split-flow, more zonal regime across the conus, with primary model discrepancies arising from the evolution of digging western US troughing, then subsequent ejection of across the Gulf states and deep south. Timing differences and depth of southern stream energy translates into differing deterministic model solutions over the W Atlantic towards the end of the medium range. Official grids will trend towards the 12z ECMWF in the latter medium range, which is better supported by the 00z eps and 12z gefs means. Worth mentioning that by Wed 12z, both model camps do converge with a fairly strong cold front and another round of strong W to NW winds spreading over the W Atlantic. Given the model spread leading up to this event, and given the fact that this is at the tail end of the period, intend to cap winds to 30 kt with the afternoon issuance and await future guidance - but would not be surprised to see gales headlines Tue night into Wed at some point.
Seas: 12z ECMWF wam initialized much better across the W Atlantic at 18z, and will use the output through the entirety of the forecast period.
Extratropical storm surge guidance: no major deviation from the latest guidance appears needed at this time, with little chance for a significant positive surge event along the East Coast over the next few days.
.Nt1 New England waters... .anz805...Georges Bank west of 68w... gale Saturday. Gale possible Saturday night. .Anz900...Georges Bank east of 68w... gale Saturday. Gale possible Saturday night. .Anz810...South of New England... gale Saturday. Gale possible Saturday night. .Anz815...South of Long Island... gale Saturday.
.Nt2 mid-Atlantic waters... .anz820...Hudson Canyon to Baltimore Canyon... gale Saturday. .Anz915...Hudson Canyon to the great South Channel... gale Saturday. Gale possible Saturday night. .Anz920...Baltimore Canyon to the great South Channel... gale Friday night into Saturday. .Anz905...The great South Channel to the Hague line... gale today. Gale Friday night into Saturday. Gale possible Saturday night. .Anz910...East of the great South Channel and south of 39n... gale today. Gale Friday night into Saturday. Gale possible Saturday night. .Anz925...Outer waters from Baltimore Canyon to Hatteras Canyon... gale Friday night.
.Forecaster Collins. Ocean prediction center.