A Hurricane Boundary Layer Model for Simulating Surface Winds during Hurricane Landfall

When the hurricane moves from sea to land, it encounters a rougher surface with increased friction that affects the boundary layer structure over land. The hurricane boundary layer (HBL) flow adjusts to the land surface conditions causing a rapid decrease in wind speed at the coastline. Moreover, there are significant changes in the wind structure over water due to the strong near-surface low-level jet in the offshore flow and a weaker higher one in the onshore flow. Parametric wind models commonly used in storm surge modeling are typically too simplistic and are not capable of properly representing these changes in the wind structure during hurricane landfall. We apply a hurricane boundary layer model that utilizes the physical balances in the dynamic equations to determine how the hurricane boundary layer responds to local variability in the surface conditions (primarily topography and surface roughness). The governing equations for the mean wind components are similar to those described in Gao and Ginis (2016) but modified for the Cartesian coordinate system. It incorporates high vertical (30 m) and horizontal (500 m) resolutions combined with high-resolution information about topography and land use. At the upper boundary, the mean wind is assumed to be under the gradient wind balance. The spatial distribution of the gradient wind, V_g, is prescribed, and the pressure gradient force, derived from the gradient balance equation, is assumed vertically uniform. A parametric wind model or output from a numerical weather prediction model can be used to specify the spatial distribution of V_g. We will discuss model simulations of recent and historical hurricane events as well as comparisons with available raw observations. This includes the observations collected during the Atlantic hurricane database reanalysis project.