Abstract
Anthropogenic climate change is intensifying tropical cyclones, and some studies suggest that they are now impacting regions farther from the equator, though uncertainties remain. This study examines the North Atlantic (NATL) basin’s autumn climatology, focusing on environments conducive to tropical transitions (TTs), as most cyclones affecting Europe that originate from TTs occur during this season. Ten CMIP6 climate models under the historical, SSP2-4.5 and SSP5-8.5 scenarios are used, covering the 1981–2100 period, with the ERA5 reanalysis employed as a reference to support the results. The study introduces the Tropical Transition Favorability Index (TTFI), which is a novel metric that integrates key parameters to quantify environmental favorability for TTs in the NATL. Findings indicate a progressive tropicalization of the NATL basin under both SSP2-4.5 and SSP5-8.5, with a more pronounced effect under the latter, driven by increased sea surface temperatures and humidity, while dynamic constraints weaken. Although in some cases the magnitude of projected future changes is comparable to existing CMIP6 models biases with respect to ERA5, the results suggest a higher likelihood of TTs, increasing the risk from these destructive systems.
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Data availability
The selected CMIP6 climate models data can be obtained from the Earth System Grid Federation (ESGF) dataset, which is available online at: https://aims2.llnl.gov/search. Observational data from the ERA5 reanalysis can be obtained from the Copernicus Climate Data Store, available online at: https://cds.climate.copernicus.eu/datasets. The code used for the calculation of the TTFI in the NATL basin covering from 1981 to 2100, based on several CMIP6 models and ERA5, and the composite of the TTFI for a set of observed TT events in the NATL for the period 1981 – 2010, based on ERA5, are available from the corresponding author upon reasonable request.
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Acknowledgements
This work is partially supported by the research project PID2023-146344OB-I00 (CONSCIENCE) financed by MICIU/AEI /10.13039/501100011033 and by FEDER, UE. This work is supported by the Interdisciplinary Mathematics Institute of the Complutense University of Madrid. This work is also supported by the ECMWF Special Projects SPESMART and SPESVALE. C. Calvo-Sancho acknowledges the grant awarded by the Spanish Ministry of Science and Innovation - FPI program (PRE2020-092343). C. Calvo-Sancho acknowledges support from the GVA. PROMETEO Grant CIPROM/2023/38 and CSIC-LINCGLOBAL Ref. LINCG24042.
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A.M.M. conducted the research, performed the analysis and drafted the article. C.C.S. contributed to the interpretation of the results and reviewed the article. J.J.G.A. contributed to the research and interpretation of the results and reviewed the article. J.D.F. reviewed the article. P.B. reviewed the article and contributed to the research. M.L.M. contributed to the research, supervised the work, reviewed the article, and contributed to the interpretation of the results. All authors have read and approved the final manuscript.
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Montoro-Mendoza, A., Calvo-Sancho, C., González-Alemán, J.J. et al. Strengthening of favorable environments for North Atlantic tropical cyclogenesis in midlatitudes in a warmer climate. npj Clim Atmos Sci (2026). https://doi.org/10.1038/s41612-025-01317-0
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DOI: https://doi.org/10.1038/s41612-025-01317-0
