García‐López et al. (2026) Rainy Season Onset in Central America and the Influence of the ENSO Decaying Phase

Identification

• Journal: Journal of Climate
• Year: 2026
• Date: 2026-10-27
• Authors: Alan A. García‐López, Ángel G. Muñoz, Richard Seager, Ron. L. Miller
• DOI: 10.1175/jcli-d-25-0706.1

Research Groups

• Department of Earth and Environmental Sciences (DEES), Columbia University, New York, New York, USA
• Lamont-Doherty Earth Observatory (LDEO), Columbia University, Palisades, New York, USA
• Aerthydral Collective, an Alisios Corporation’s NPO, Granada, Spain
• NASA Goddard Institute for Space Studies, New York, New York, USA

Short Summary

This study investigates the physical mechanisms driving rainy season onset in Central America, focusing on the independent and joint influences of ENSO and Tropical North Atlantic sea-surface temperature, to improve early warning systems for rainfall deficits. It reveals that El Niño typically delays onset by over 7 days due to tropospheric warming, while La Niña generally hastens it, but complex Pacific-Atlantic interactions can still lead to delays, particularly on the Caribbean side of northern Central America.

Objective

• To describe and understand the physical mechanisms related to delayed rainy season onset in Central America, providing a framework for early warning systems.
• To present a generalized approach for computing rainy season onset and analyzing its physical drivers and intraseasonal evolution.
• To analyze the independent and joint influences of the El Niño-Southern Oscillation (ENSO) and the sea-surface temperature of the Tropical North Atlantic (TNA) on rainy season onset in Central America.

Study Configuration

• Spatial Scale: Central America, specifically northern Central America and the Caribbean side of northern Central America, including regions within the Central American Dry Corridor.
• Temporal Scale: Analysis period from 1981 to 2022, focusing on boreal spring and intraseasonal evolution.

Methodology and Data

• Models used: Not explicitly stated; the study employs a "generalized approach" to compute rainy season onset based on observational/reanalysis data.
• Data sources: High-resolution daily rainfall data, moist static stability, vertically-integrated moisture convergence, low-level winds, and sea level pressure anomalies.

Main Results

• Strongly delayed rainy season onsets (more than 7 days) occur over northern Central America in the boreal spring following the peak of El Niño events, primarily driven by tropospheric warming induced by El Niño.
• La Niña events generally lead to a modest hastening of the rainy season onset due to tropospheric cooling.
• Despite the general hastening effect of La Niña, certain regions in northern Central America still experience delayed onsets during these events.
• La Niña events coupled with a warm Tropical North Atlantic (TNA) significantly delay onset over the Caribbean side of northern Central America.
• This specific delay during La Niña with a warm TNA is attributed to a reduction in surface moisture caused by an anomalous low-level circulation, likely induced by an extratropical wave-train, rather than by the TNA warming itself.

Contributions

• Provides a generalized approach for computing rainy season onset and analyzing its physical drivers and intraseasonal evolution, which can support early warning systems.
• Offers a detailed description and understanding of the physical mechanisms behind delayed rainy season onset in Central America.
• Highlights the critical importance of considering Pacific-Atlantic basin interactions and their impact on the mid-troposphere for diagnosing rainfall characteristics and rainy season onset in Central America.
• Elucidates the complex, non-linear influences of ENSO and TNA, including specific scenarios where La Niña, combined with TNA conditions, can still lead to significant delays.

Funding

No funding information was provided in the abstract.

Citation

@article{GarcíaLópez2026Rainy,
  author = {García‐López, Alan A. and Muñoz, Ángel G. and Seager, Richard and Miller, Ron. L.},
  title = {Rainy Season Onset in Central America and the Influence of the ENSO Decaying Phase},
  journal = {Journal of Climate},
  year = {2026},
  doi = {10.1175/jcli-d-25-0706.1},
  url = {https://doi.org/10.1175/jcli-d-25-0706.1}
}