Freak waves under typhoon conditions

Benjamin-Feir Index (BFI) and directional spread are measures of nonlinear four-wave interactions and resultant indices of possible conditions for freak waves. Temporal-spatial distributions of BFI and directional spread are examined with numerical simulations of a spectral wave model using typhoon conditions. The spatial distributions of wave characteristics such as significant wave height, wave period, BFI and directional spread are different from each other around the eye of the typhoon. BFI is significantly large in the fourth quadrant of the typhoon, while waves are steep and have narrow frequencies and directional spectra. Freak waves resulting from nonlinear four-wave-wave interactions have a greater potential of occurring in the fourth quadrant of the typhoon than in the other quadrants. Furthermore, crossing sea states from two-wind-wave systems can be observed behind the eye of the typhoon. The crossing, two-wind systems are also dangerous sea states, although as observed, they are closer to linear wave conditions. Finally, the characteristics of possible freak wave conditions during typhoons are verified with field data.