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000 AGNT40 KWNM 251210 MIMATN Marine Weather Discussion for N Atlantic Ocean NWS Ocean Prediction Center Washington DC 810 AM EDT Sat Mar 25 2017 .FORECAST DISCUSSION...Major features/winds/seas/significant .weather for the North Atlantic Ocean W of 50W from 30N to 50N. A cold front continues to sink S across the NT1 waters with the WSW gradient to its immediate likely still having winds up to 25 or 30 kt. Max seas in this gradient are likely in the 7-10 ft range which are being handled somewhat better by the higher 00Z ECMWF WAM versus the 06Z Wavewatch III at the moment. Over the short term, the 06Z NAM/GFS remain consistent versus their previous respective runs and in reasonably good agreement with the other 00Z global models. Therefore will continue to use the previously populated 00Z GFS solution for the cold front to continue to sink S today, stall tonight across the N central NT2 waters tonight/Sun (with a moderately strong (20-25 kt Ely gradient developing immediately N of the front), then drift back slowly NE as a warm front Sun night into Mon night with a weak frontal wave tracking NE across the NT1 waters Mon night. So will just make some minor tweaks to the previously populated 00Z GFS winds through Mon night in deference to the 06Z GFS/00Z ECMWF. In the long range, the 06Z GFS has trended slightly stronger with a developing surface low forecast to track NE across the Nrn waters Tue night/Wed while pulling a trailing cold front SE across the area. But with there still being large disparity between the latest global models regarding this system, for now will continue to use the previously populated 00Z GFS/ECMWF compromise solution with just some minor tweaks in deference to the 06Z GFS. ----------------------------------------------------------------- PREVIOUS DISCUSSION... The most recent Ascat overpasses across the offshore waters from 0050Z to 0230Z indicated southwest winds to 30 kt across the northern NT2 zones and to 25 kt elsewhere north of Hatteras Canyon. Although the most recent model guidance all initialized some winds to 30 kt, Ascat shows more widespread 30 kt than initialized. However, the higher 00Z GFS first sigma level winds are too high. As a result, and after some testing some different model blends, came up with a 2:1 00Z GFS first sigma level and 00Z ECMWF boundary layer wind blend that best matched the Ascat. At 06Z the cold front had moved off the New England coast and the 00Z models are in good agreement that the front will slowly move south across the NT1 and northern NT2 waters today into tonight, before stalling off the Delmarva peninsula late tonight into early Sunday. Models are also consistent that the west to southwest widns south of the cold front will gradually diminish through the day today, to less than 25 kt later this evening. Then as high pressure builds off the New England coast tonight into Sunday night, the 00Z GFS/NAM/Canadian are somewhat stronger than the 00Z ECMWF/UKMET with the easterlies just poleward of the stationary front across the southern NT1 and northern NT2 waters Sunday into Sunday night. This discrepancy in the models` wind speeds north of the front persists late Sunday night into Monday night as the front lifts northeast back across the NT1 waters as a warm front. OPC preference continues with these slightly higher winds to 25 kt. For wind grids will use the blend noted above through tonight, before transitioning to the 00Z GFS Sunday through Monday. In the medium range, the 00Z models diverge greatly with a series of weak upper shortwaves moving through the northeastern US and off the northern mid Atlantic and/or New England coasts Tuesday night and Wednesday. The GFS has been consistently stronger with the associated developing low and cold front forecast to move offshore late Tuesday and Wednesday. There also continued to be farily widespread differences with the timing of this system. The 00Z models then become more consistent later Wednesday night into Thursday that the aformentioned shortwaves and approaching northern stream trough will consolidate into an upper low across southeastern Canada and Maritimes. Given model discrepancy, have decided to use a blend of the 00Z GFS and 00Z ECMWF for wind grids Tuesday night through Wednesday night, which offers a compromised timing with the front. However did adjust these blended winds upward by about 10 percent to get some associated winds to 25 kt. We have above average forecast confidence that winds across the NT1 or NT2 offshore waters should remain below gale through at least midweek. .Seas...The 00Z Wavewatch III is slightly better initialized than the 00Z ECMWF WAM with wave heights across the west Atlantic this morning. However, the 00Z WW3 may not be high enough across the nothern NT2/southern NT1 zones where there are still some 30 kt winds occurring. Am preferring to use an even blend between this guidance through the forecast period. .Extratropical Storm Surge Guidance...N/A. .WARNINGS...Preliminary. .NT1 New England Waters... None. .NT2 Mid-Atlantic Waters... None. $$ .Forecaster Vukits/Clark. Ocean Prediction Center.

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