Merrimack River Mouth Swell ForecastUnited StatesMAEssex CountyMerrimack River Mouth1-Day3-Day5-Day Graph Plots Open in Graphs Swell Height and Direction Forecast NOAA WaveWatch III Swell Period Forecast NOAA WaveWatch IIIMerrimack River Mouth swell forecast issued yesterday at 7:49 pm. Next forecast at approx. 7:49 pm.Get WillyWeather+ to remove ads