A Physical Interpretation of Recent Tropical Cyclone Post-Landfall Decay

The decay of landfalling tropical cyclones is important to the damage caused. We examine a simple physically based decay model of maximum surface winds driven by frictional turbulent drag and a modification accounting for partial to complete land roughness. The model fits an algebraic decay with a parameter determined by the ratio of the surface drag coefficient to the effective vortex depth. This parameter has been decreasing from 1980 to 2018. There is also a global mean increase of wind speed 24 h after landfall of +1.13 m/s per decade. We cannot exclude the possibility that this trend is driven by the initial wind speed increase, but it is most likely due to a slowing of the decay. This weaker decay amounts to an additional 7 h of gale force winds for a typical Category 1 at landfall.

Automated summary

Research indicates that the decay rate of landfalling tropical cyclones is gradually slowing, resulting in an increase in wind speed within 24 hours after landfall. The trend may be driven by an initial increase in wind speed or a slowing of the decay rate.