Projected changes in extreme windstorms and high-wind cyclone tracks across model resolutions

Extreme windstorms cause substantial socioeconomic damage across many Northern Hemisphere regions, yet uncertainty remains whether their frequency will increase or decrease under global warming. Here, using a multi-member ensemble of HighResMIP global models (low- to high-resolution, coupled and atmosphere-only) together with regional dynamically downscaled simulations, we investigate future changes of extreme windstorms and their dynamical origins. Results suggest extreme windstorms over the northeastern USA and southeastern Canada will increase significantly, regardless of model resolution or coupling strategy, and consistently across global and regional simulations. This increase occurs despite a decline in overall mid-latitude cyclone numbers and is driven by more intense cyclones — including transitioning tropical cyclones — tracking into the region. Low-resolution simulations produce more frequent and larger windstorms than high-resolution ones, due to the lower 99th-percentile wind speeds and hence exceedance threshold and their larger eddy length scale which implies overestimation of the Rossby deformation radius. Low-resolution simulations also exhibit higher low-level baroclinicity and available potential energy (APE), yet weaker eddy kinetic energy (EKE) than simulations performed at high resolution. This indicates less efficient APE-to-EKE conversion. Our findings reveal a robust projected increase in extreme windstorm risk for northeastern North America and underscore that quantitative projections of synoptic-scale hazards require atmospheric grid spacing of ~25–50 km, finer than the ~100 km traditionally considered adequate for synoptic-scale modeling.