Marine Weather for HS 100


marine weather discussion for N Atlantic Ocean NWS ocean prediction center Washington DC 409 am EDT Wed Oct 18 2017

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

High pressure will persist to the west of the forecast waters and a relaxed pressure gradient across the region will keep winds below gale force threshold. Geocolor satellite images show mostly clear skies inland west of the forecast waters but mostly cloudy areas over the southern waters with some convection confined to the far southern and southeastern waters. This is in line with inland high pressure and a surface cold front across the southeastern and far southern waters. Winds are mainly from the northeast with weaker winds over the north areas and they increase southward with maximum winds to 30 kt over the southern waters in the vicinity of the front. NCEP map at 06z still has inland high pressure over the southern states that extends its ridge northeast across the mid Atlantic states into New England and that has northeast winds to the east which is mainly the forecast waters. Another high pressure 1030 mb to the east of the southern waters generates southwest winds to the east of the region. Low pressure 1003 mb northeast of the waters has its cold front that stretches southwest into another low pressure 1012 mb 240 nm east of the Baltimore Canyon, front continues southwest between the two highs, just east of the waters then into the southern waters. Latest scatterometer pass at 0244z this morning indicated areas of 30 kt winds confined to the far southern portion of zone anz935.

Models GFS/CMC/ukmethr/ecmwfhr/NOGAPS/NAM/gfsmean have initialized the 06z main synoptic features fairly well with just minor differences on the actual position for the central pressure value of the inland high and ukmethr is the only model that does not have a closed low just east of the Baltimore Canyon but a deep trough. Models have trended weaker and have pushed highest winds that were east of the forecast waters farther east. In the short term, models have a general agreement on keeping high pressure just west of the region and that will block strong frontal boundaries from reaching the waters and so the pressure gradient will remain relaxed over the waters through the forecast period. The models have also indicated some instability to persist over the southeastern waters as indicated by the persistent negative lifted index and that will sustain some mixing that will keep winds relatively higher to the southeast of the Gulf Stream with maximum winds over the far southern waters. Will continue with GFS for consistency and also that models are in generally good agreement.

.Seas...Seas are relatively smaller to the north of the Gulf Stream with 6 ft along the Gulf Stream and just 2 ft over the far northwest waters. Otherwise, seas mostly range between 6 and 9 ft except the southeastern zones where seas are over 9 ft with a peak at 13 ft. Jason 3 pass about 1908z returned peak significant wave height of 13 ft over the southeastern waters. Nww3 generally fits very well the observed seas pattern but just underdone by a foot on the peak value. Ecmwfwave matches the peak value but not so much in line with observations to the north as it extends its 6 ft line farther north of the Gulf Stream. As such, an equal blend of the two wave models is a better compromise and so will go ahead with a blend.

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


.Nt1 New England waters... None.

.Nt2 mid-Atlantic waters... None.


.Forecaster musonda. Ocean prediction center.

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