A Simple Diagnostic for Assessing Internal Dynamical Constraints on Tropical Cyclone Intensity

The upper bound of tropical cyclone (TC) intensity is usually estimated from the available thermodynamic energy in the environment. But internal dynamics of the vortex also put constraints on TC intensity. Here we show quantitatively the internal constraints on maximum wind speed using a simple diagnostic computed from maximum wind speed, radius of maximum wind, and latitude of the storm. With global observations and reanalysis data of TCs during 2001-2020, this diagnostic is found to occur in more than half of the storms with rapid intensification, and coincides with drastic halt of rapid intensification despite little change in the environment (e.g., sea surface temperature, relative humidity, and wind shear). This diagnostic highlights the importance of pressure-wind relationship in internal dynamical control on storm intensity, and provides a valuable tool to improve the understanding, modeling, and prediction of storm intensity evolution.