Can Existing Theory Predict the Response of Tropical Cyclone Intensity to Idealized Landfall?

TL;DR

This study tests and extends existing tropical cyclone intensity theories to predict storm weakening after landfall, demonstrating that combined surface effects and empirical decay models align with theoretical predictions.

Contribution

The paper generalizes potential intensity theory to include weakening, and shows that combined surface roughening and drying effects can be predicted by multiplying individual responses.

Findings

Transient response to surface roughening matches a frictional spin-down model.

Theoretical predictions align with empirical decay models for real storms.

Potential for existing theory to forecast inland cyclone intensity decay.

Abstract

Tropical cyclones cause significant inland hazards, including wind damage and freshwater flooding, that depend strongly on how storm intensity evolves at and after landfall. Existing theoretical predictions for the time-dependent and equilibrium response of storm intensity have been tested over the open ocean but not yet to be applied to storms after landfall. Recent work examined the transient response of the tropical cyclone low-level wind field to instantaneous surface roughening or drying in idealized axisymmetric f-plane simulations. Here, experiments testing combined surface roughening and drying with varying magnitudes of each are used to test theoretical predictions for the intensity response. The transient response to combined surface forcings can be reproduced by the product of their individual responses, in line with traditional potential intensity theory. Existing intensification theory is generalized to weakening and found capable of reproducing the time-dependent inland intensity decay. The initial (0-10min) rapid decay of near-surface wind caused by surface roughening is not captured by existing theory but can be reproduced by a simple frictional spin-down model, where the decay rate is a function of surface roughness. Finally, the theory is shown to compare well with the prevailing empirical decay model for real-world storms. Overall, results indicate the potential for existing theory to predict how tropical cyclone intensity evolves after landfall.