Secondary Eyewall Formation for Idealized and Real Tropical Cyclones in HWRF

Secondary eyewall formation (SEF) and a potential ensuing eyewall replacement cycle (ERC) is a common occurrence in developed tropical cyclones (TCs). The ERC can have a profound impact on the overall structure of the TC; as a result, improving the predictability of SEF is critical to forecasting TC intensity. Despite their commonality in nature, idealized and real-data numerical simulations continue to struggle with developing the secondary eyewall structures. Recent studies have suggested that a combination of low-level dynamics within the boundary layer and microphysical processes outside of the boundary layer are critical to SEF. Due to the horizontal and vertical resolution for operational models, these boundary layer and microphysical processes must be parameterized.

In our current research, idealized simulations are conducted using the Hurricane Weather Research and Forecast (HWRF) modeling system. The evolution of the idealized TC strength and structure is shown to be highly sensitive to the parameterization of the boundary layer and microphysical processes. The resulting TC structure either permits or prohibits the SEF that can later lead to an ERC. Preliminary results suggest a need to better understand the linkage between the boundary layer processes and the microphysical processes in order to better predict the SEF and ERC in an operational setting.