Secondary Eyewall Forecast in HWRF

We introduce HWRF as the first mesoscale numerical model that consistently generates secondary eyewalls in its operational setting. While secondary eyewalls are common in nature, with about 80% of Saffir-Simpson Category 3 hurricanes and equivalent in the Atlantic and western Pacific exhibiting them, mesoscale numerical simulations generating them have been relatively rare. We describe the extent to which HWRF generates secondary eyewalls in the operational setting, analyze the qualitative characteristics of these eyewalls and discuss implications for secondary eyewall forecast.

The boundary layer parameterization is uncovered as key in the generation of secondary eyewalls in HWRF. Comparisons of different operational versions of HWRF (with different physics) and comparisons of idealized simulations of the model differing only on the boundary layer parameterization, serve as the basis to establish clarity of the role of the boundary layer parameterization on the generation of secondary eyewalls.