An “extended fetch” model for the spatial distribution of tropical cyclone wind–waves as observed by altimeter

• The largest ever database of tropical cyclone waves has been analysed.
• The wave field depends on velocity of forward movement and maximum wind speed.
• This dependence results from the extended fetch caused by the translating tropical cyclone.
• A parametric model is developed to define the tropical cyclone wind field.
• This model can be used to predict the wave height and spectrum.

An extensive database of altimeter measurements of wind speed and significant wave height is analysed to investigate the spatial distribution of significant wave height within tropical cyclones. The database includes transects of 440 tropical cyclones. As such, the data covers the full range of expected values of the velocity of forward movement, maximum wind velocity and radius to maximum winds. The data confirms previous measurements that JONSWAP scaling can be used to represent such waves. In addition, the data supports the concept of an extended fetch in such systems. The maximum waves occur when the wind direction and direction of propagation of the storm are aligned. In such cases, the waves move forward with the storm and experience an extended fetch. A parametric model based on JONSWAP scaling and representing the extended fetch is developed and optimized using the data. Combined with previous in situ measurements, this model can reproduce the spatial distribution of significant wave height, as well as estimate the full directional spectrum.