North Atlantic Marine Weather Discussion
AGNT40 KWNM 061411 MIMATN Marine Weather Discussion for N Atlantic Ocean NWS Ocean Prediction Center Washington DC 911 AM EST Thu Dec 6 2018 .FORECAST DISCUSSION...Major features/winds/seas/significant .weather for the North Atlantic Ocean W of 50W from 30N to 50N. Per the 12Z NCEP surface analysis a strong 980 mb hurricane force low was located E of the northern NT2 waters near 40N60W. A high pressure ridge was located over the immediate NT1 and NT2 waters itself. The intermediate 06Z GFS/NAM were in agreement with the 00Z ECMWF and other 00Z guidance through the first half of the weekend. With this, plus the continued uncertainty in terms of the exact track regarding the weekend coastal low expected to impact the OPC offshore waters, I see no reason to make adjustments to the ongoing forecast in place. Current wind warning headlines will remain as is for this intermediate update. Continue to anticipate winds subsiding below gale force today over the NE NT2 waters as the aforementioned strong low E of the waters continues to pull away to the NE as high pressure ridging continues to build in from the W. Then expect a return of gales over the weekend as the aforementioned coastal low begins to impact the region. Please see the previous discussion for additional information. ----------------------------------------------------------------- PREVIOUS DISCUSSION... The Ascat wind retrievals from 0050 UTC and 0126 UTC last night indicated winds to 45 kt across the nrn outer NT2 offshore waters in the vicinity of the Gulf Stream, and an area of gales in the central NT2 waters in the cold advection. The higher winds are W of a developing low currently just E of the area, and the 00Z models indicate the low will rapidly intensify as the winds increase to hurricane force E of the offshore waters within the next 6 to 12 hours. The 00Z GFS and ECMWF both indicate gales in the cold advection over the offshore waters early today, and the models have been consistent on the timing and intensity for the past few runs. The 00Z high resolution NMM seems representative when compared with the data, so planning on starting out with the NMM model in the next forecast. The 00Z models then indicate a weak cold front will pass through NT1 and nrn NT2 tonight and Fri, before indicating a significant coastal storm developing off the SE coast Sun and impacting the offshore waters through Mon. There has been somewhat poor run to run consistency in the models, with all of the global models changing on the track run to run. The 00Z ECMWF is near the 00Z GFS into Mon, then the GFS becomes a bit faster than the rest of the guidance with the system. However, the models all form several lows over the srn offshore waters over the course of a few days late in the period, and most of the differences show up in the mid level H5 vorticity with multiple shortwaves moving through the area. Since the guidance doesn't agree well on the details, am preferring the 00Z ECMWF through Mon. Am then preferring the 05/12Z ECMWF from 00Z Tue onward as it is near continuity with the track, and confidence in the 00Z guidance is low on the track so preferring to not make any significant changes on it. As far as the winds are concerned, all solutions show winds increasing to gale force Sun, and this is supported by the upper levels in the GFS/ECMWF which show the development in the right entrance region of a very strong jet streak while a shortwave trough moves off the coast. As a result, confidence is above average on the gale headlines Sun into Mon, though below average on anything higher than that as a result of the poor support. For that reason, am planning on continuing with previous headlines in the next forecast. .SEAS...The 00Z ECMWF WAM is initialized slightly high over the central NT2 waters this morning, but within a foot of the 06Z observations over the remainder of the offshore waters. The models agree somewhat in the short range, then diverge in the medium range as a result of the previously mentioned differences with the associated atmospheric models. In order to remain consistent with the forcing from the preferred winds, will populate with the 00Z ECMWF WAM into 00Z Tue, then transition to the 05/12Z ECMWF WAM thereafter. .EXTRATROPICAL STORM SURGE GUIDANCE...The 00Z ESTOFS and ETSS shows a surge moving along the SE coast associated with the developing coastal low moving into the area on Sun. The GFS seems too fast with the low, so the surge guidance which is driven by the GFS forcing is likely too fast as well. However, values in excess of 3 ft along the SE coast Sat night seem representative of the expected system, though come up too fast. Coastal interests should continue to monitor the latest forecasts from coastal National Weather Service forecast offices for further information. .WARNINGS...Preliminary. .NT1 New England Waters... None. .NT2 Mid-Atlantic Waters... .ANZ905...The Great South Channel to the Hague Line... Gale today. .ANZ910...East of the Great South Channel and south of 39N... Gale today. .ANZ925...Outer Waters from Baltimore Canyon to Hatteras Canyon... Gale Possible Sunday night into Monday. .ANZ830...Inner Waters from Currituck Beach Light to Cape Hatteras... Gale Possible Sunday night into Monday. .ANZ833...Inner Waters from Cape Hatteras to Cape Fear... Gale Possible Sunday into Monday. .ANZ930...Outer Waters from Hatteras Canyon to Cape Fear... Gale Possible Sunday into Monday. .ANZ835...Inner Waters from Cape Fear to 31N... Gale Possible Sunday into Monday. .ANZ935...Outer Waters from Cape Fear to 31N... Gale Possible Sunday into Monday. $$ .Forecaster Holley/Kells. Ocean Prediction Center.