The ECCOFS domain spans the eastern seaboard of North America and Intra-Americas Seas from the Grand Banks of Newfoundland in the north to the mouth of the Orinoco River, Venezuela, in the south. ECCOFS will complement the existing WCOFS (West Coast Operational Forecast System) to achieve complete forecast coverage of U.S. territorial seas adjacent to the 48 contiguous states and Puerto Rico. Each day ECCOFS generates an ocean analysis using the Regional Ocean Modeling System (ROMS) 4-Dimensional Variational (4D-Var) data assimilation (DA) system constrained by ocean observations. The forecast resolution is 3 km in the horizontal at 50 vertical terrain-following levels.