Wind-wave steepness offshore the North American east coast

Wind-wave steepness along the North Atlantic (27.46 N < lat < 43.53 N and 62.03 W < lon < 80.19 W) is characterized based on at most 37 years (1984 to 2020) of buoy measurements. Wave data from 16 National Data Buoy Center (NDBC) and 2 Marine Environmental Data Section (MEDS) stations located at depths ranging from 33 m to 5394 m are used. Intra-annual variability of the full spectrum wave steepness (s_m) and the wind-sea steepness (s_mw) are analyzed. Among the 18 locations, the average s_m and s_mw ranged between 0.023 to 0.037 and 0.025 to 0.039, respectively. Results show similar intra-annual variability among the different buoys both for s_m and for s_mw with monthly average maximums occurring between January and February (0.029 < s_m < 0.045, 0.030 < s_mw < 0.048) and minimums between July and August (0.018<s_m<0.033, 0.019 < s_mw < 0.035). The probability distribution function of s_m/s_mw presents a peak between 0.9 and 1.0 for all stations. It is also found that the sea states with the maximum s_m and s_mw are not directly linked to the maximum events of significant wave height. Practically, these findings can inform the implementation of various ocean engineering endeavors as well as navigation risk determination, as wave steepness exerts a significant influence on several physical processes in the marine environment.