The theory of trapped-fetch waves with tropical cyclones - An operational perspective

The majority of high wave events and almost all cases of extreme or phenomenal wave growth are the result of a high degree of synchronicity between moving storms and the waves that they generate. This wave containment or resonance phenomenon, referred to as trapped-fetch waves, has been known for generations, but not always well understood by forecasters. The twofold threat of trapped-fetch waves is that they have the potential for extreme growth, yet are unheralded by leading swell. Conceptual and numerical Lagrangian reference frame experiments on wave containment are presented, illustrating the influence on tropical cyclone ocean waves by three storm parameters: storm speed, wind speed, and fetch length. To further illustrate the concepts and provide real-time application, a simple, desktop Lagrangian trapped-fetch wave model, used for training and operational assessment of trapped-fetch waves, is described in a companion article.