NOAA GFDL - Geophysical Fluid Dynamics LaboratoryGFDL - Geophysical Fluid Dynamics Laboratory

Non-Uniform Reduction of the North Atlantic Tropical Cyclones in Response to the AMOC Weakening Under External Freshwater Forcing

August 27th, 2026

Key Findings

  • A weakened Atlantic Meridional Overturning Circulation (AMOC) under external freshwater forcing reduces North Atlantic tropical cyclone activity in high-resolution coupled model experiments.
  • The storm reduction varies across the basin, with different responses in tropical cyclone genesis locations and storm tracks.
  • The non‐uniform storm reduction is linked to the equatorward spread of cold and dry conditions along the North Atlantic horseshoe pathway and the enhanced vertical wind shear over the tropical North Atlantic
  • Direct storm tracking (instead of indirect inferences from large‐scale environmental changes) provides a framework for examining how tropical cyclone activity responds to changes in large-scale ocean circulation.

Rajat Joshi and Rong Zhang. Geophysical Research Letters. DOI: 10.1029/2026GL123615

The Atlantic Meridional Overturning Circulation (AMOC) is a system of ocean currents that transports heat within the Atlantic Ocean and influences ocean conditions across the basin. In this study, the authors examine how North Atlantic tropical cyclones respond to AMOC weakening caused by external freshwater forcing. Because tropical cyclones are influenced by oceanic and atmospheric conditions, changes in large-scale ocean circulation can affect where storms form and how they evolve.

The analysis uses high-resolution simulations from the fully coupled model (GFDL CM4C192), including an idealized freshwater-forcing ensemble and a corresponding control ensemble. Tropical cyclones are identified and tracked using the GFDL tropical cyclone tracker, allowing direct assessment of storm frequency, genesis locations, and tracks, instead of indirect inferences from large‐scale environmental changes. The simulations show that AMOC weakening under external freshwater forcing reduces tropical cyclone activity across the North Atlantic, but the response is not spatially uniform. Storm frequency and track behavior vary by region and evolve over time. These differences occur alongside shifts in environmental conditions during the Atlantic hurricane season, including sea surface temperature, latent heat flux, near-surface humidity, atmospheric temperature, zonal wind, and vertical wind shear. Specifically, the non-uniform storm reduction is related to the equatorward spread of cold and dry conditions (an unfavorable environment for tropical cyclones) along a horseshoe pathway over the North Atlantic and the enhanced vertical wind shear over the tropical North Atlantic.

The findings describe how large-scale ocean circulation influences the oceanic and atmospheric conditions that affect tropical cyclone development. It also demonstrates the use of high-resolution coupled modeling and direct storm tracking to examine relationships between AMOC and Atlantic tropical cyclone behavior.

Spatial maps of the global tropical cyclone (TC) genesis locations and the seasonal cycle of the North Atlantic TC counts. (a) Spatial distribution of all season TC genesis locations (red dots) from observations (IBTrACS) summed over the period 1981–2020. (b) Climatological seasonal cycle of the North Atlantic TC counts (storms/year): observations over 1981–2020 (black) and the ensemble-mean over the last 40 years for the control (blue) and water hosing (red) experiments. (c–h) Same as (a) but summed over the last 40 years of each control and water hosing ensemble members. Observations are shown for 1981–2020 to match the last 40-year period used for model results.