How Important Are Post‐Tropical Cyclones for European Windstorm Risk?

Post‐tropical cyclones (PTCs) extend many hazards associated with tropical cyclones (TCs) to the midlatitudes. Despite recent high‐impact cases affecting Europe such as Ophelia, little research has been done to characterize the risk of PTCs. Here we compare the climatologies and intensity distributions of midlatitude cyclones (MLCs) and PTCs in the North Atlantic and Europe by tracking cyclones in the ERA5 reanalysis. Considering hurricane season cyclones impacting Northern Europe, PTCs show a significantly higher mean maximum intensity than MLCs, but make only a small contribution to total windstorm risk. Our results show that a disproportionately large fraction of high‐intensity cyclones impacting Europe during hurricane season are PTCs. The fraction of PTCs impacting N Europe with storm force (>25 m s−1) winds is ~10 times higher than that for MLCs. Less than 1% of cyclones impacting Northern Europe are identified to be PTCs. This rises to 8.8% when considering cyclones which impact with storm force winds. Ex‐hurricanes (post‐tropical cyclones; PTCs) can bring hazardous weather such as damaging winds and extreme precipitation to the midlatitudes. The importance of these cyclones for European wind and flood risk is still an open question. By tracking cyclones through 39 years of data, we show that on average, the maximum intensity of PTCs over Europe is significantly higher than that for European windstorms (midlatitude cyclones, MLCs). The difference between the maximum intensity of PTCs and MLCs is larger across Northern Europe than Southern Europe. Our results show that a disproportionately large fraction of high‐intensity cyclones impacting Northern Europe during hurricane season are PTCs. The fraction of PTCs impacting Northern Europe with storm force winds is ~10 times greater than for MLCs. Less than 1% of cyclones impacting Northern Europe during the North Atlantic hurricane season are PTCs. This rises to 8.8% when only considering cyclones which impact Northern Europe with storm force winds. Post‐tropical cyclones are significantly more intense than midlatitude cyclones at their maximum intensity over EuropeThe fraction of post‐tropical cyclones impacting northern Europe with storm force winds is 10 times higher than that for midlatitude cyclonesA disproportionately large fraction of high‐impact European windstorms forming in hurricane season are caused by post‐tropical cyclones