A 30 m scale modeling of extreme gusts during Hurricane Irma (2017) landfall on very small mountainous islands in the Lesser Antilles

Abstract

Abstract. In view of the high vulnerability of the small islands of the Lesser Antilles to cyclonic hazards, realistic very fine scale numerical simulation of hurricane-induced winds is essential to prevent and manage risks. The present innovative modeling aims at combining the most realistically simulated strongest gusts driven by tornado-scale vortices within the eyewall and the most realistic complex terrain effects. The Weather Research and Forecasting (WRF) model with the nonlinear backscatter and anisotropy (NBA) large eddy simulation (LES) configuration was used to reconstruct the devastating landfall of category 5 Hurricane Irma (2017) on Saint Barthélemy and Saint Martin. The results pointed out that the 30 m scale seems necessary to simulate structures of multiple subtornadic-scale vortices leading to extreme peak gusts of 132 m s−1 over the sea. Based on the literature, such extreme gust values have already been observed and are expected for category 5 hurricanes like Irma. Risk areas associated with terrain gust speed-up factors greater than 1 have been identified for the two islands. The comparison between the simulated gusts and the remote sensing building damage highlighted the major role of structure strength linked with the socio-economic development of the territory. The present modeling method could be easily extended to other small mountainous islands to improve the understanding of observed past damage and to develop safer urban management and appropriate building standards.

Storm‐Scale and Fine‐Scale Boundary Layer Structures of Tropical Cyclones Simulated With the WRF‐LES Framework

“…In the experiments, the PBL parameterization scheme is turned off in the sub-kilometer domains and the LES technique is used. For the LES experiments, the nonlinear backscatter with anisotropy SGS parameterization scheme are used, which are consistent with model configurations in previous LES experiments (Cécé et al, 2021;Green & Zhang, 2015;Mirocha et al, 2010;Wu et al, 2018Wu et al, , 2019. The scheme was implemented into the WRF version 3.0 for improved LES performance at coarser resolutions and improvements in computational efficiency (Mirocha et al, 2010).…”

Atlantic Offshore Wind Transmission Study

“…The wind gust a tower structure is subjected to depends on the surrounding terrain characteristics. Cécé et al (2021) focuses on modeling extreme wind gusts experienced during the landfall of Hurricane Irma in 2017 on small mountainous islands in the Lesser Antilles. Figure K-7 illustrates the computed wind gust speed-up factor (ratio of local wind speed to nearby areas) in complex terrain.…”

“…Effects of Saint Martin Island terrain on the wind gust speed-up factor. Image fromCécé et al (2021)…”

Tropical Cyclone Changes in Convection‐Permitting Regional Climate Projections: A Study Over the Shanghai Region

“…While tropical cyclones have a spatial scale of hundreds or even thousands of kilometers, they contain small scale features that are critical to their impacts such as the maximum wind speed and central pressure. Using large eddy simulation, Rotunno et al (2009) found no convergence in tropical cyclone properties even at resolutions below 100 m and Cécé et al (2021) found that 30 m seems necessary to produce the vortices which result in the most extreme wind gusts of 132 m s 1 over the sea. However, the use of convection-permitting regional climate models (CPMs in the rest of the paper) run at a horizontal resolution of a few kilometers, gives significant improvements in the simulation of tropical cyclones over models with lower resolutions (Knutson et al, 2020;Prein et al, 2015;Taraphdar et al, 2014).…”