Rogue waves at low Benjamin-Feir indices: Numerical study of the role of nonlinearity

The nonlinear interaction between waves in incoherent sea states is weaker than their dispersion. In this situation, random space-time focusing is the main mechanism of the formation of rogue waves. The numerical simulation has indicated that nonlinearity becomes important at the final stage of focusing and can significantly change predictions of the so-called second-order theory concerning the parameters of rogue waves. The elongation of the crest of a rogue wave as compared to that predicted by the second-order theory is an important effect promoting the weighting of the tails of the distribution function of the vertical deviation of the free surfaces.