Marine Weather for HS 100


marine weather discussion for N Atlantic Ocean NWS ocean prediction center Washington DC 432 PM EDT Fri Sep 20 2019

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

Post-tropical cyclone Humberto continues to weaken and kick east of the offshore waters this afternoon. While the associated wind field has shifted E of the offshores, large NE residual swells continue across the waters this afternoon. For the past 24-36 hours guidance has consistently initialized 3-5 ft too low, and both the 12z and 18z wave analysis times proved no different. In fact the altimeter instrument flying aboard Sentinel-3a actually measured conditions nearly doubled from guidance where these swell were opposing the Gulf Stream just E of the waters near 38n 64w. It serves a good reminder for extreme caution to mariners for localized very rough conditions in or along the Gulf Stream in opposing winds and or seas.

Residual swell should steadily diminish overnight as high pressure along the coast shifts a little east and settles atop the waters. High remains nearly stationary into Sun night, then then shifts E of the area Sun night into Mon ahead of the next approaching shortwave. A weak to moderate cold front will approach the New England coast Mon and Mon night, move offshore Tue, then pass across the waters Tue night. Another high pressure ridge will build across the area behind the boundary Wed and Wed night. The afternoon models remained in above average agreement with the timing of this front as well as with advertising some winds to 25 kt ahead of it over the nt1 and some northern nt2 zones late Sun night into Mon night.

Further out in the medium range, attention is then again turned to the tropics as Hurricane Jerry is expected to track northwest toward the southern offshores Mon and Mon night, then turn more NE Tue and re-curve well E of the area Tue night through Wed night. Model trends have consistently been weakening the storm and offering a much slower forward speed, and interests should be monitoring NHC forecasts to track the progress of Jerry over the next several days. While the bulk of the wind grids will be based on the 12z GFS, Tue through Wed night will likely be any model that is closest to the upcoming NHC advisory at 5 PM - preliminarily, this looks to be a version closest to the 12z ECMWF.

Seas: as mentioned above will make significant edits in the first 3-6 hours of the grids to increase seas to match actual obs. Otherwise, will trend the grids to the ww3 throughout the forecast period.

Extratropical storm surge guidance: the 12z estofs and 12z etss both show any lingering surge should gradually subside overnight. Then throughout the remainder of the forecast period, significant positive surge is not expected along the mid-Atlantic or New England coasts. Please see the forecasts from your local NWS forecast office for more detailed information.


.Nt1 New England waters... None.

.Nt2 mid-Atlantic waters... None.


.Forecaster Collins. Ocean prediction center.

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