Importance of Initial Vortex Wavenumber-1 Asymmetries to Tropical Cyclone Intensification

Tropical cyclones (TCs) frequently exhibit considerable asymmetries in their inner core during the intensification phase. However, most operational forecasting models fail to adequately represent these asymmetric structures in their initial conditions. Using a series of idealized numerical experiments, this study investigates how initial inner-core vortex asymmetries influence TC intensification. Our results demonstrate that wavenumber-1 asymmetries—closely associated with the vertical tilt of TC vortices—play a critical role in determining the timing of intensification onset. Specifically, intensification only begins once the wavenumber-1 asymmetries align in a particular configuration relative to the axisymmetric circulation. When the initial vortex lacks or misrepresents these asymmetries, additional time is required for the TC’s vertical structure to adjust. These findings suggest that improving the representation of wavenumber-1 asymmetry in TC initial conditions could improve intensity forecasts in numerical models.