Sea Level Variations of the United States (1854 to 1999) Derived from 117 National Water Level Observation Network Stations

Water level records are a combination of the fluctuations of the ocean and the vertical land motion at the location of the station. Monthly mean sea level (MSL) variations were analyzed for 117 stations of the National Ocean Service's (NOS) National Water Level Observation Network (NWLON) having between 25 and 146 years of data. The sea level variations determined are the linear trend, the average seasonal cycle, and the interannual variability at each station. Monthly data up to the end of 1999 were used in the calculation and all stations had data spanning a period of 25 years or more. Since the derived trends include the local vertical land motion, they are spatially variable. Calculated MSL trends range from 9.85 mm/yr for Grand Isle, LA to -16.68 mm/yr for Skagway AK, and are consistent with previous trends published by NOS. Available data from this project include time series plots for each station of the monthly MSL with the seasonal cycle removed, a 5-month average, and the linear trend with its 95% confidence interval which was obtained after accounting for the average seasonal cycle; the seasonal cycle; the Interannual variation of mean sea level for all data to 1999; and the Interannual variation from 1980 to the present (updated monthly). The location and timing of any major earthquakes near stations in tectonically-active areas are noted since an associated vertical offset or a change in MSL trend is possible.