New ways to measure waves and their effects at NOAA tide gauges

The standard deviation (sigma) of continuous 1-second water level sampling is used at 46 U.S. NOAA tide gauges available since 1996 as a high-frequency variance measure. Sigma estimates local infragravity and incident wave band variability, is significantly correlated (r = 0.5-0.9) to significant wave height (Hs) and scales linearly to local observations and output from the global ocean wave (GOW) reanalysis at most ocean-exposed, reef-lined and harbor-sheltered coast locations. Empirical orthogonal functions of daily mean sigma from 6 Hawaii tide gauges distinguish northerly and southerly modes that closely match local Hs observations. Depending on tide gauge location, the 99^th % of daily maxima sigma can be as large as or larger than the nontidal residual component of the water level sample. Our findings provide new uses of land-based tide gauge data to estimate offshore significant wave heights and local dynamic water levels, both of which are required for monitoring local conditions during storm events and measuring the severity of related impacts.