FVCOM provides ocean model data for the Gulf of Maine and a number estuaries in the Gulf of Maine. The model data is delivered via OPeNDAP services at a number of sigma depth levels and a different time periods. The mesh (compised of nodes and elements or facets) is pretty easy to navigate, and oceanographic state variables are provide.
You can read more about it on the github page for the fvcom R package. Recent updates include refreshing stale links, removing unneccessary dependencies and providing stars output if one wants to rasterize a portion of the mesh.