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Although El Niño‐Southern Oscillation (ENSO) and its global impacts through teleconnection have been known for decades, if and how the mean currents and mesoscale eddies in the Caribbean Sea are linked to ENSO remains an open question. Here, by analyzing satellite observations and an ocean reanalysis product, we found a close connection between mean currents, eddies in the Caribbean Sea and ENSO on interannual timescales. Strong El Niño events result in enhanced north‐south sea surface height differences and consequently stronger mean currents in the Caribbean Sea, and the opposite happens during La Niña events. The eddy kinetic energy responds to ENSO via eddy‐mean flow interaction, primarily through baroclinic instability, which releases the available potential energy stored in the mean currents to mesoscale eddies. Our results suggest some predictability of the mean currents and eddies in the Caribbean Sea, particularly during strong El Niño and La Niña events. 

Eddies in the northwestern tropical Atlantic Ocean play a crucial role in transporting the South Atlantic Upper Ocean Water to the North Atlantic and connect the Atlantic and the Caribbean Sea. Although surface characteristics of those eddies have been well studied, their vertical structures and governing mechanisms are much less known. Here, using a time-dependent energetics framework based on the multiscale window transform, we examine the seasonal variability of the eddy kinetic energy (EKE) in the northwestern tropical Atlantic. Both altimeter-based data and ocean reanalyses show a substantial EKE seasonal cycle in the North Brazil Current Retroflection (NBCR) region that is mostly trapped in the upper 200 m. In the most energetic NBCR region, the EKE reaches its minimum in April–June and maximum in July–September. By analyzing six ocean reanalysis products, we find that barotropic instability is the controlling mechanism for the seasonal eddy variability in the NBCR region. Nonlocal processes, including advection and pressure work, play opposite roles in the EKE seasonal cycle. In the eastern part of the NBCR region, the EKE seasonal evolution is similar to the NBCR region. However, it is the nonlocal processes that control the EKE seasonality. In the western part of the NBCR region, the EKE magnitude is one order of magnitude smaller than in the NBCR region and shows a different seasonal cycle, which peaks in March and reaches its minimum in October–November. Our results highlight the complex mechanisms governing eddy variability in the northwestern tropical Atlantic and provide insights into their potential changes with changing background conditions.