On the Intensity Decay of Tropical Cyclones Over the Ocean

Understanding the decay of tropical cyclones (TCs) from their lifetime maximum is important because it is this final phase that determines landfall wind speed and damage. Wang and Toumi (2022) developed a logistic model which describes the intensity decay as the residual between frictional dissipation from surface drag and energy production by heat fluxes. This logistic model has been validated against the over-ocean decay of TCs that make landfall. Here we show that the logistic model also fits well to the over-ocean decay of global TCs whether they make landfall. Both the observed decay and the corresponding fitted curve are characterised by a decay rate that slows down over time, or a decay rate decreases with decreasing intensity. This consistency suggests that the intensity decay is dominated by surface friction. In addition, our composite analysis of environmental conditions shows that the temporal intensity decay is accompanied by ocean cooling and increasing vertical wind shear. Those unfavourable environmental conditions affect the decay rate by causing a reduction in the heat fluxes term in the logistic model. The intensity decay is influenced by both the surface friction and the environmental conditions.

Reference:

Wang, S., Toumi, R. On the intensity decay of tropical cyclones before landfall. Sci Rep 12, 3288 (2022). https://doi.org/10.1038/s41598-022-07310-4