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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 ms-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. [ABSTRACT FROM AUTHOR]

In view of the high vulnerability of the Lesser Antilles small islands 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 realistic 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 islands. The results pointed out that the 30-m scale seems necessary to simulate intense 400-m scale vortices leading to extreme peak gusts like 132 m s-1 over sea. Risk areas associated with terrain gust speed-up factors greater than one have been identified for the two islands. The comparison between the simulated gusts and the remote sensing building damages 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 damages and to develop safer urban management and appropriate building standards. [ABSTRACT FROM AUTHOR]

This study aims to better understand coastal processes associated with extreme cyclonic events through the study of the coastal changes, flooding and damage that resulted from the passage of a category 5 hurricane (Irma) on 6 September 2017 over the islands of Saint-Martin and Saint-Barthélemy in the Lesser Antilles. Hurricane Irma was contextualized from tropical cyclone track data and local weather observations collected by Météo-France, as well as high-resolution numerical modelling. Field work involved the study of accretion coasts through qualitative observations, topo-morphological and sedimentary surveys, as well as image acquisition with Unmanned Aerial Vehicle (UAV) surveys during two trips that were made 2 and 8 months after the catastrophe. Wave propagation and flood numerical models are presented and compared to field data. Our field analysis also reports on the devastating impacts of storm surges and waves, which reached 4 and 10 meters height, respectively, especially along east-facing shores. The approaches reveal a variety of morpho-sedimentary responses over both natural and highly urbanized coasts. The analysis shows the effects of coastal structures and streets on flow channeling, on the amplification of some erosion types, and on water level increase. Positive spatial correlation is found between damage intensity and marine flood depth. The signatures of ocean-induced damage are clear and tend to validate the relevance of the intensity scale used in this study. [ABSTRACT FROM AUTHOR]