marine weather discussion for N Atlantic Ocean NWS ocean prediction center Washington DC 322 PM EST Fri Feb 15 2019
.Forecast discussion...Major features/winds/seas/significant .Weather for the North Atlantic ocean W of 50w from 30n to 50n.
Per the 18z NCEP surface analysis a high pressure ridge was located across the nt1 and nt2 waters. The latest ascat hires data where available revealed 20-30 kt winds over the NW nt1 waters. Over the nt2 waters 15-25 kt winds were noted over the inner N and central parts, with 10-20 kt winds over the S parts.
The 12z model cycle was similar to it's prior 00z run, and the 06z runs of the GFS/NAM when compared to the o0z cycle, in terms of it's good agreement through Sunday night with spread in the guidance arising later Sunday night into Monday night in regards to low pressure expected to move E across the nt2 waters. With that noted feel it'll be reasonable to continue with the existing grids over the forecast period, though some tweaks to the grids through Sunday night will be made, more so to better match some isc edit areas where needed. Those existing grids being a 50/50 blend of the 00z GFS/ECMWF. The 12z GFS/ECMWF/UKMET are in good agreement that a cold front will move E and then across the nt1 and nt2 tonight through tomorrow night, with a weak low developing along the front over the southern nt2 waters later tomorrow, before moving E of the waters tomorrow night. Confidence in pre-frontal gales over the Gulf of main tonight into the overnight hours remains above average as the 12z GFS/NAM/ECMWF/navgem all show areas of 35 kt winds with the 12z UKMET at 30 kt. Of note the 12z Gem is the most bullish, as it tends to be at times, with guidance depicting winds up to 50 kt ahead of the front but that will be discounted in this forecast. Anticipate winds subsiding below gale force heading into tomorrow morning as the the front clears the nt1 waters and high pressure ridging begins to build in. Concerning the low pressure developing over the southern nt2 waters along the southern tail end of the front later tomorrow, right now guidance is in agreement in suggesting winds will remain below warning criteria as the low traverses the waters.
The next system of interesting will be low pressure moving E off the eastern Seaboard and across the nt2 waters sometime late Sunday night through Monday or Monday night. While guidance is in agreement on low pressure moving through the waters, differences remain in terms of the exact track through the nt2 waters, the timing of the low and strength. The 12z ECMWF/navgem/NAM appear to be the faster of the guidance initially, placing the low just E of the N nt2 waters Monday, with the 12 GFS/Gem low position over the central N nt2 waters and the 12z UKMET with a low position over the mid-Atlantic. By Monday all guidance has the low E of the waters, but with the 12z ECMWF/NAM and now navgem farther NE with the low center compared to the 12z GFS/Gem which have the low roughly 300 nm E of anz905. Also again varying degrees of strength are depicted in the guidance with the 12z GFS/Gem suggesting gales over parts of the central or N nt2 waters, the 12z UKMET showing a broad area of 30 kt winds both ahead and behind the associated cold front, the 12z NAM holding off on gales until the low clears the waters, and the 12z ECMWF only showing a small area of 30 kt winds ahead of the front. These differences noted here are why I feel it's reasonable to not make adjustments to the ongoing grids in place for the Sunday night into Monday night time frame and feel a persistence forecast is better served here.
For the remainder of the period high pressure ridging builds into the nt1 and nt2 waters behind the low by Tuesday morning, with low pressure troughing developing along the se coast Tuesday night into Wednesday. Models actually show decent agreement amongst themselves concerning this scenario, so here feel using the existing grids is reasonable. For the very end of the period, later Wednesday into Wednesday night low pressure is progged by the guidance to develop off the se coast, then move towards the central nt2 waters. Again this is depicted in the 12z GFS/ECMWF/UKMET/navgem/Gem but with spread concerning the exact location of the low come Wednesday night and the very end of the period. Am confident that winds will increase across several of the S and central nt2 zones in response to the presence of the low but to what exact extend is too hard to pin down right now. Hence, given the decision to continue with mainly a persistence forecast up to this point, that doing the same for Wednesday day 5, with the differences among the guidance just noted, makes sense.
.Seas...Will continue with the existing wave grids given the choice to continue with the existing wind grids, those grids consisting of a 50/50 blend of the 00z wavewatch iii/ECMWF wam.
.Extratropical storm surge guidance...No significant positive surge events are expected during the next couple of days. For more details please monitor the latest forecast and information from your local National Weather Service office.
.Nt1 New England waters... .anz800...Gulf of Maine... gale today into tonight. .Anz805...Georges Bank west of 68w... gale today.
.Nt2 mid-Atlantic waters... None.
.Forecaster Holley. Ocean prediction center.