Ground-Based Radar Observations of Boundary-Layer Wind Profiles during the Landfall of Hurricane Ida 2021

Hurricanes are one of the most destructive natural disasters impacting infrastructure, economies, and coastal environments. One key area of current research is understanding how the hurricane boundary layer (HBL) transitions during and after landfall, which is crucial for improving hurricane intensity and structure forecasts over land. Previous studies sometimes noted the existence of logarithmic wind profiles in the HBL over both the ocean and in the near-surface layer over land. This “log-layer” assumption is used to estimate near-surface winds when surface measurements are unavailable. However, the existence of the log-layer within the HBL has been questioned primarily due to inhomogeneities in the boundary-layer wind profiles near the inner core of a hurricane as well as the development of an internal boundary layer (IBL) in coastal regions resulting from an increase in surface roughness. To assess the validity of the “log-layer assumptions”, this study investigates HBL wind profiles using the Velocity Azimuth Display (VAD) analysis of the NWS New Orleans (KLIX) Doppler radar observations during the landfall of Hurricane Ida (2021). By pairing the VAD wind profiles with 10-m sustained wind measurements from the Automated Surface Observing System (ASOS) station near KLIX over a 10-h period, we identified a separate log-layer within the emerging, shallow IBL over land under certain circumstances. Factors affecting the existence of a log layer will be discussed. Additionally, comparison of the estimated surface roughness from the VAD profile and the true value at the KLIX site will be presented to further discuss the caveats of using the log-layer assumption to infer near-surface wind speeds during hurricane landfalls. The improved understanding of the HBL wind profile evolution can also provide insight into the processes leading to tornadogenesis during hurricane landfalls.