Constructive interference of two wave groups

The formation of an extreme crest via constructive interference of two wave groups (swell+wind) according to the Quasi-Determinism (QD) theory (Boccotti, 1989). The swell travels faster than the wind waves, so the wind wave group must lead the swell to align in phase and focus at the center of the domain. This makes large crests in crossing seas less likely than in unimodal seas, where crests can build atop isolated focusing wave groups. In crossing seas, the swell and wind wave groups must be properly spaced according to their group speeds—a rarer configuration. As a result, the probability of such a joint event is lower than that of a single, isolated group. Second-order effects can be included easily, and modulational instability is negligible in this case.