Theoretical model of rainfall in tropical cyclones for the assessment of long-term risk

We propose a theoretical model to evaluate the rainfall intensity field due to large-scale horizontal wind convergence in tropical cyclones (TCs). The model is intended as one component of a methodology to assess the risk of extreme rainfall intensities from TCs. The other components are a recurrence relation for the model parameters and track and a statistical representation of the deviations of rainfall intensity from model predictions. The latter are primarily caused by rainbands and local convective activity and is the focus of an upcoming communication. The vertical flux of moisture and the associated surface rain rate are calculated using basic thermodynamics and a simple numerical model for the vertical winds inside the TC boundary layer. The tropical cyclone is characterized by the radial profile of the tangential wind speed at gradient level, the storm translation velocity, the surface drag coefficient, and the average temperature and saturation ratio inside the TC boundary layer. A parametric analysis shows the sensitivity of the symmetric and asymmetric components of the rainfall field to various storm characteristics.