Montoro-Mendoza et al. (2026) Strengthening of favorable environments for North Atlantic tropical cyclogenesis in midlatitudes in a warmer climate

Identification

Journal: npj Climate and Atmospheric Science
Year: 2026
Date: 2026-01-09
Authors: A. Montoro-Mendoza, C. Calvo-Sancho, J. J. González-Alemán, J. Díaz-Fernández, P. Bolgiani, M. L. Martín
DOI: 10.1038/s41612-025-01317-0

Research Groups

Department of Applied Mathematics, Faculty of Computer Engineering, Universidad de Valladolid, Spain
Consejo Superior de Investigaciones Científicas (CSIC), Instituto de Geociencias (IGEO), Madrid, Spain
Centro de Investigaciones sobre Desertificación (CIDE, CSIC-UV-GVA), Climate, Atmosphere and Ocean Laboratory (Climatoc-Lab), Moncada, Valencia, Spain
Agencia Estatal de Meteorología (AEMET), Department of Development and Applications, Madrid, Spain
Department of Earth Physics and Astrophysics, Faculty of Physics, Universidad Complutense de Madrid, Spain
Interdisciplinary Mathematics Institute, Universidad Complutense de Madrid, Spain

Short Summary

This study investigates how anthropogenic climate change influences environments favorable for tropical transitions (TTs) in the North Atlantic, revealing a progressive tropicalization of the basin, particularly in mid-latitudes, under future warming scenarios. It introduces a novel Tropical Transition Favorability Index (TTFI) to quantify these changes, showing a significant increase in TT-conducive conditions.

Objective

To examine the climatology of North Atlantic (NATL) environments conducive to tropical transitions (TTs) during autumn (September, October, November; SON) and assess how anthropogenic climate change (ACC) will impact these patterns.
To define and apply a novel Tropical Transition Favorability Index (TTFI) to provide a more precise assessment of environmental conditions favoring TTs development.

Study Configuration

Spatial Scale: North Atlantic (NATL) basin, covering 0°N to 70°N latitude and 90°W to 0°E longitude.
Temporal Scale: 1981–2100, analyzed across three 30-year periods: historical (1981–2010), near future (2021–2050), and far future (2071–2100). The study focuses on the autumn months (September, October, November; SON).

Methodology and Data

Models used: A composite of ten Coupled Model Intercomparison Project Phase 6 (CMIP6) climate models: IPSL-CM6A-LR, INM-CM4-8, MIROC6, HadGEM3-GC31-MM, EC-Earth3, MPI-ESM1-2-HR, CESM2-WACCM, MRI-ESM2-0, NorESM2-MM, and GISS-E2-1-G.
Data sources: CMIP6 climate model simulations for historical, SSP2-4.5, and SSP5-8.5 scenarios; ERA5 global reanalysis dataset for historical baseline and reference; HURDAT database for observed tropical transition cases.

Main Results

A progressive tropicalization of the North Atlantic basin is projected under both SSP2-4.5 and SSP5-8.5 scenarios, with a more pronounced effect under the latter.
Sea Surface Temperature (SST) shows widespread warming across the NATL, with statistically significant positive anomalies. The area where SST exceeds 298.65 K (25.5 °C), a threshold for tropical cyclogenesis, expands poleward and intensifies in the late-century period.
Total Column Water (TCW) exhibits statistically significant positive anomalies across most of the domain, indicating enhanced atmospheric moisture content. These anomalies intensify markedly in the far future, particularly under SSP5-8.5, with the largest increases concentrated between 0°N and 30°N.
Vertical Wind Shear (WSH) projections show contrasting responses:
- Under SSP2-4.5, positive WSH anomalies (increased shear) are projected across the tropical and central-western Atlantic, which would suppress TT development.
- Under SSP5-8.5, widespread and statistically significant negative WSH anomalies (reduced shear) are observed between 10°N and 50°N in the far future, suggesting a more favorable environment for TT occurrence.
Atmospheric stability (minimum Coupling Index, min CI) shows statistically significant reductions (up to -12 K in some northern areas) over most of the domain, indicating a more unstable atmosphere that favors deeper convection and strengthens TTs. The area with min CI values below 295.65 K (22.5 °C) expands substantially.
The novel Tropical Transition Favorability Index (TTFI) shows a statistically significant increase across the NATL basin, particularly in the central-western region, with anomaly values reaching up to +12 TTFI Units in the far future under SSP5-8.5.
Regions exceeding the 4 TTFI Unit threshold (observed minimum for real TT formation) expand considerably under both future scenarios, especially northeastward, implying greater TT activity and potential impacts along the eastern NATL coast.
The spatial mean of the TTFI 95th percentile (P95) exhibits statistically significant positive trends, with the rate of increase being more pronounced under the SSP5-8.5 scenario, consistent with an observed increase in real TTs density and TTFI values in recent decades.

Contributions

Introduces and validates a novel Tropical Transition Favorability Index (TTFI) that integrates key thermodynamic and dynamic parameters to quantify environmental favorability for tropical transitions (TTs) in the North Atlantic.
Provides a comprehensive multi-model assessment using ten CMIP6 climate models to project future changes in NATL environments conducive to TTs under both moderate (SSP2-4.5) and extreme (SSP5-8.5) climate change scenarios.
Demonstrates a progressive tropicalization and a significant poleward and eastward expansion of favorable TT environments in the NATL, highlighting an increased risk of intense TT-originating cyclones impacting mid-latitude regions, including Europe.
Offers insights into the complex interplay between increasing sea surface temperatures, humidity, and changes in wind shear and atmospheric stability in driving future TT activity.

Funding

Research project PID2023-146344OB-I00 (CONSCIENCE) financed by MICIU/AEI /10.13039/501100011033 and FEDER, UE.
Interdisciplinary Mathematics Institute of the Complutense University of Madrid.
ECMWF Special Projects SPESMART and SPESVALE.
Spanish Ministry of Science and Innovation - FPI program (PRE2020-092343) for C. Calvo-Sancho.

Citation

@article{MontoroMendoza2026Strengthening,
  author = {Montoro-Mendoza, A. and Calvo-Sancho, C. and González-Alemán, J. J. and Díaz-Fernández, J. and Bolgiani, P. and Martín, M. L.},
  title = {Strengthening of favorable environments for North Atlantic tropical cyclogenesis in midlatitudes in a warmer climate},
  journal = {npj Climate and Atmospheric Science},
  year = {2026},
  doi = {10.1038/s41612-025-01317-0},
  url = {https://doi.org/10.1038/s41612-025-01317-0}
}

Original Source: https://doi.org/10.1038/s41612-025-01317-0