National Tidal Datum Epoch

The National Tidal Datum Epoch (NTDE) is the specific 19-year period over which tide observations are averaged to compute the official US tidal datums: Mean Sea Level, Mean High Water, Mean Higher High Water, Mean Low Water, and Mean Lower Low Water. The 19-year span includes the 18.61-year lunar nodal cycle, so it captures the full modulation of tidal range and ties datums to one consistent reference. The current epoch is 1983 through 2001, adopted by NOAA in 2003 and scheduled to move to 2002 through 2020. Re-epoching recomputes over 2,000 datums and bench-mark sheets.