Trapped-fetch waves in a transitioning tropical cyclone (part I—the need and the theory)

Forecast centres responsible for ocean wave prediction during tropical cyclone events are often left with unsatisfactory numerical guidance from wave models because of the models’ strong dependence on atmospheric wind models. The problem of predicting maximum significant wave heights with a tropical cyclone becomes critical to the right of the storm’s track where the potential exists for a considerably enhanced fetch. This phenomenon is illustrated in the companion poster presentation on Hurricane Luis.

Using established wave theory, a quick and reliable estimation of maximum significant wave heights can be determined from only three variables: wind speed (the component in the direction of the system’s motion); system speed; and the fetch length within the storm. A simple nomogram–-for predicting maximum significant wave heights–-developed for Canadian Hurricane Centre (CHC) meteorologists, will be presented, highlighting the sensitivity between system speed and fetch enhancement / reduction. The nomogram is tested against the wave reports from Gert (1999); Bonnie (1998); Danielle (1998); Felix (1995); and Luis (1995).

The nomogram is converted to a computer algorithm which has been coupled with the CHC’s analytical wind model. Both models are part of HURR, the CHC operational meteorologists’ TC analysis and prediction software tool. In the companion poster session, details of the model and case studies will be presented.

Note: HURR was presented at the 22nd Conference in Fort Collins and the analytical wind model was presented at the 23rd Conference in Dallas.