Abstract:
Hurricane landfalls are associated with extreme wind hazards and cascading impacts, yet reliably estimating near-surface winds remains a major challenge. This difficulty stems in part from limited understanding of the sustained winds and gusts within the internal boundary layer (IBL) that develops in response to abrupt changes in surface roughness at landfall. This study addresses this gap using semi-idealized large-eddy simulations (LES) to simulate the landfall of high-end Category-2 hurricane-force winds over a range of land surface roughness conditions.
The first half of the seminar examines how varying land surfaces modulate vertical profiles of near-surface mean winds and turbulence properties within the coastal IBL. Given the IBL’s partial dynamical decoupling from the flow aloft, the ability of coastal radars and radiosondes to detect and represent this feature is evaluated. For the first time, uncertainties in 10-m wind estimates from commonly used observation-based methods are quantitatively assessed. The second half of the seminar focuses on wind gusts, leveraging high-frequency LES output to examine their evolution in coastal transition zones. While 10-m sustained winds rapidly weaken to tropical-storm force inland, localized gusts equivalent to EF-1 to EF-2 intensity remain prevalent within the coastal transition zone, posing severe, highly localized wind hazards. An along-trajectory momentum budget analysis is conducted to identify the physical processes responsible for the formation of these extreme near-surface gusts, offering a potential explanation for the observed localized damage swaths during hurricane landfalls (e.g., Hurricane Andrew, 1992). Together, these findings provide insights that can inform the development of probabilistic 10-m wind forecasting products, supporting the goals of NOAA’s Hurricane Forecast Improvement Project (HFIP).