I know how to estimate the 100-year wave height from a time series of wave measurements, but not how to estimate the wave period associated with the 100-year height. Let's say based on a 20-year time series of sea surface elevation measurements, the 100-year height is estimated to be Hs=15m, but meanwhile the highest observed wave in this period is Hs=13m. How is the period associated with Hs=15m estimated?

Presently I am calculating it as follows: (a) For 0.5m-bins of wave height extending from Hs>2m to Hs=13m, I calculate the most probable wave period for that bin (in other words, at Hs=2.5m it's Ta=9 seconds, at Hs=3m it's 10 seconds, etc). (b) I fit a line to those most probable periods. (c) I extend the line to Hs=15m.

Is there a better or more standard way to estimate the period associated with a 100-year Hs?