Storm Amy likely intensified by both human driven climate change and natural variability

Contact Authors

• Mireia Ginesta, Oxford Sustainable Law Programme - University of Oxford, UK  📨mireia.ginesta@smithschool.ox.ac.uk  🗣️English, Spanish, Catalan

• Davide Faranda, IPSL-CNRS, France  📨davide.faranda@lsce.ipsl.fr    🗣️English,French, Italian

Citation

Ginesta, M., & Faranda, D. (2025). Storm Amy likely intensified by both human driven climate change and natural variability. ClimaMeter, Institut Pierre Simon Laplace, CNRS. https://doi.org/10.5281/zenodo.17284501

Press Summary

• Storms similar to Amy are up to 2 hP deeper, up to 4 km/h  (10%) windier over the Atlantic coasts of Ireland and France, and up to 3 mm/day (up to 10%) wetter in the present than they would have been in the past.

• Storm Amy was driven by very rare meteorological conditions.

• Natural variability alone cannot explain the increase in rain and wind linked to Storm Amy.

Event Description

Storm Amy was a rapidly deepening North Atlantic extratropical cyclone and the first named storm of the 2025/26 UK–Ireland season. The remnants of Hurricanes Humberto and Imelda interacted with the North Atlantic jet stream, accelerating its flow and contributing to the rapid intensification of the low-pressure system that became Storm Amy.

The system tracked eastwards from the mid-Atlantic and reached the UK and Ireland between Friday 3 October and Saturday 4 October 2025, bringing its strongest impacts during that period. Advance warnings were issued for 2–4 October. Although there was some uncertainty about the exact magnitude of the storm, most major forecast models — including those from the UK Met Office, ECMWF, GFS, and ICON — consistently predicted a period of very strong winds and heavy rainfall across the UK and Northern Ireland. A peak gust of 96 mph (155 km/h) was recorded on the Island of Tiree at the height of the storm. The storm showed a central pressure of 947.9hPa at Baltasound, Shetland, exceeding the previous October record of 950.9hPa in 1988.

The strong winds and heavy rain caused widespread travel disruption, fallen trees, power outages, and significant coastal impacts across Scotland, northern England, and much of Ireland. In Ireland, the most severe conditions occurred in the west and northwest, where authorities issued orange and red wind and flood warnings. One storm-related fatality was confirmed in County Donegal. Storm Amy also brought severe weather to parts of continental Europe, including Norway, Sweden, Belgium, and France. On Saturday afternoon, powerful gusts associated with the storm resulted in two fatalities in northern France, where authorities issued an orange-level weather alert.

The Surface Pressure Anomalies reveal a large negative (cyclonic) anomaly over Scotland with values up to -8hPA. In the context of Atlantic extratropical storms, this setup can be associated with extensive precipitation and intense wind due to the deepening pressure gradient. Temperature Anomalies show temperatures up to 4 °C warmer than average over the  UK, affected by the warm sector of the cyclone. Precipitation Data show intense daily precipitation (up to 50 mm/day) over Ireland, UK, France and North Sea. Windspeed data show large areas of UK and France affected by sustained winds between 40 km/h and 60 km/h, and higher than 60 km/h over the Northern sea.

Climate and Data Background for the Analysis

The IPCC AR6 Chapter 11 states that climate change affects storminess in Europe, with negative repercussions that are exacerbated by rising sea levels and heavy precipitation. From a global warming level of 2 °C or higher a slightly increased frequency and amplitude of extratropical cyclones, strong winds and extratropical storms is projected for northern Europe with medium confidence (IPCC AR6 WGI Chapter 12). The extreme precipitation and pluvial flooding have shown a strong trend in Northern Europe in the past and there is a strong consensus among models from global to kilometer scale convection permitting models that are going to increase from 2 °C or higher  (IPCC AR6 WGI Chapter 12). Studies, such as Ginesta et al. (2024), confirm that the intensity of recent storms, including both wind speed and precipitation, is likely to increase in the most impacted regions of Europe.

Our analysis approach rests on looking for weather situations similar to those of the event of interest having been observed in the past. For storm Éowyn, we have medium-high confidence in the robustness of our approach given the available climate data, as the event is similar to other past events in the data record.

ClimaMeter Analysis 

We analyze here (see Methodology for more details) how events similar to the meteorological conditions leading to the  Storm Amy have changed in the present (1987–2023) compared to what they would have looked like if they had occurred in the past (1950–1986) in the region [20°W 5°E 46°N 62°N]. The Surface Pressure Changes show that storms similar to Amy are up to 2 hPa deeper in the present climate, with an increase in the horizontal pressure gradient in the southeastern sector of the storms. Temperature Changes show that present-day events are up to +1.5°C warmer in the storm Amy warm sector compared to similar past storms. Precipitation Changes show wetter conditions, with up to +3 mm/day (around +10%) more rainfall. Windspeed Changes show significant increases of up to +5 km/h in coastal and offshore areas.

We also note a slight shift in storm seasonality: storms now tend to occur more often at the start of the season, whereas in the past they were more frequent toward the end. Changes in urban areas reveal that Glasgow, Belfast and Dublin experience windier and wetter conditions in the present than in the past.

Finally, we find that sources of natural climate variability, notably the El Nino—Southern Oscillation and the Atlantic Multidecadal Oscillation, may have only partly influenced the event. This suggests that the changes we see in the event compared to the past may be partly due to human driven climate change, with a contribution from natural variability.

Conclusion

Based on the above, we conclude that storms similar to Amy are 2hPa deeper, up to 3 mm/day (10%) wetter, and windier by up to 4 km/h (10%) in the present compared to the past. We interpret Storm Amy as an event of very rare meteorological conditions for which natural climate variability played a role.