Is Europe under UNSEEN Risk of Cyclones of Tropical Origin?

Traditionally, European windstorms – the costliest meteorological hazards in Europe, are associated with extratropical cyclones in winter. However, in recent years, unorthodox cyclones such as Ophelia (2017), Leslie (2018), and Kirk (2024) have had noticeable impacts on Europe during autumn. These cyclones, referred to as Cyclones of Tropical Origin (CTOs), form in tropical or subtropical regions and can migrate toward Europe during their lifecycle. Although CTOs do not always cause significant impacts, they can exhibit exceptional intensity, posing unique hazards distinct from typical extratropical cyclones.

This raises important questions: Are these isolated events? Will these events become more common in future climates? Current efforts to quantify the risk posed by CTOs are hindered by limited observational data and an incomplete theoretical understanding of these phenomena. As a result, Europe may face an unseen hazard from CTOs.

In this presentation, we analyse CTO events using a physically consistent UNSEEN event set constructed from twentieth-century seasonal hindcast outputs (CSF-20C and SEAS5-20C). Our results show that while CTOs are rare, they are not isolated. We examine the interdecadal variability of CTO impact potentials—including wind, rainfall, and compound hazards—and assess their impact probabilities during the twentieth century. Finally, we present preliminary findings that highlight the genuine and previously unseen risk posed by CTOs to Europe.