Quoted from: https://www.ncdc.noaa.gov/data-access/model-data/model-datasets/navoceano-ncom-reg 

The Fleet Numerical Meteorology and Oceanography Center (FNMOC) operates regional ocean prediction systems based on the Navy Coastal Ocean Model (NCOM). There are three regional NCOM datasets available from this site: the AMSEAS domain covers the Americas Seas region including the Gulf of Mexico and Caribbean Sea, the USEAST domain covers the U.S. East Coast, and the Alaska domain covers the northeast Pacific including the Gulf of Alaska. The regional NCOMs produce 4-day forecasts at 3-hour time steps, updated at 00Z daily. FNMOC interpolates the output onto a regular grid with 1/30 degree (~3km) resolution in the horizontal and 40 levels in the vertical; prior to April 5, 2013, the resolution was roughly 1/36 degree. The NetCDF files contain ocean temperature, salinity, eastward and northward currents, and elevation, along with the atmospheric forcing fields provided over the model domain by a 15 km application of the Navy's COAMPS model. The regional NCOM ocean prediction systems assimilate all quality-controlled observations in the region including satellite sea surface temperature and altimetry, as well as surface and profile temperature and salinity data using the Navy Coupled Ocean Data Assimilation (NCODA) system. Boundary conditions are applied from the FNMOC operational 1/12 degree Global HYCOM. Prior to April 2013, boundary conditions were applied from the Navy operational Global NCOM.

The horizontal resolution of the regional NCOM datasets was changed in April 2013, requiring that the time-aggregated datasets be split between data prior to that time and data after that time. All regional NCOM output after November 2009 has 40 depth levels, while output prior to that has 34 levels. Because the USEAST dataset spans both the vertical and horizontal resolution changes, it has been divided into three separate aggregations.

Note: Users requiring operational, 24/7/365 access to updates of this product should consider using the high-availability servers at the National Centers for Environmental Prediction (NCEP). This site provides access to Regional NCOM along with other models at the NCOM High Resolution Oceanic Model page. These and other ocean products are available on the Ocean Prediction Center page.