Nonlinear extreme wave evolution in random wave groups

Non-Gaussian statistics from a laboratory experiment with a 36-hour random wave simulation are presented. Unidirectional deep-water waves with a narrow-banded spectrum are run. Records from wave probes distributed over a large area of propagation are included. Results for the statistical skewness show good agreement with second-order theory all over the wave field. However, the kurtosis as well as the extreme crest and wave heights show significant increase beyond second-order theory after 10-15 wavelengths of propagation. Analysis of wave groups leading to the extreme events indicate that nonlinear group formation may explain the highest waves.