Explosive cyclogenesis and high-impact winds in storm Éowyn in January 2025: sensitivities to simulation setup and latent heating

In January 2025, storm Éowyn underwent one of the fastest deepening rates ever observed for an extratropical cyclone, producing wind gusts exceeding 184 km h⁻¹ along Ireland’s west coast and ranking among the five most intense storms to affect the UK in terms of central pressure. The representation of such extreme extratropical cyclones in numerical weather prediction (NWP) models remains challenging, as their structure, deepening, and associated surface weather impacts are sensitive to the choice of NWP model, initial conditions, simulation resolution and lead time, and the representation of diabatic processes. In this study, we investigate how some of these factors influence the simulated intensification of storm Éowyn, using two state-of-the-art high-resolution models in their limited-area mode: the ICOsahedral Nonhydrostatic (ICON) model and the Portable Model for multi-scale Atmospheric Prediction (PMAP). The latter model is currently under development at the European Centre for Medium-Range Weather Forecasts (ECMWF) and ETH Zürich to enable simulation of weather across scales. We also revisit the classical approach of “dry (latent heating suppressed) vs. moist” simulations to quantify the contribution of latent heating to the intensification of Éowyn. Moreover, we perform pseudo-global warming experiments to explore the sensitivity of Éowyn’s evolution with respect to thermodynamic climate perturbations, revealing possible storylines for how the severity of such extreme storms may change in a future warmer climate. We quantify the effect of horizontal resolution and lead time on the storm evolution with quantitative insights into the contributions of thermodynamic and dynamical processes that lead to the rapid intensification of extratropical cyclones and the associated formation of extreme winds.