by Kelly M. Núñez Ocasio et al.1
African Easterly Waves (AEWs) are synoptic-scale, westward-propagating atmospheric disturbances that form over sub-Saharan Africa during boreal summer. First described in the 1930s and formally named by meteorologist Herbert Riehl in 1945, these systems have been recognized for decades as precursors to Atlantic tropical cyclones, modulators of rainfall across the African Sahel, and transporters of Saharan dust across the tropical Atlantic. Despite their well-established importance, no comprehensive review of AEWs as complex high-impact weather systems has existed—until now. Our review of AEWs fills that gap, synthesizing more than 80 years of observational, theoretical, and modeling advances into a single, unified resource for the weather and climate community.
AEWs are cold-core disturbances exhibiting both horizontal and vertical tilt, consistent with their mixed baroclinic-barotropic nature. They typically have wavelengths of 2,000–6,000 km, periods of 3–5 days, and propagate westward at 7–9 m s⁻¹. They follow two distinct tracks on either side of the African Easterly Jet (AEJ): a northern, drier track associated with low-level perturbations linked to the Saharan heat low, and a southern, moister track more strongly coupled to the West African Monsoon and more frequently associated with tropical cyclone genesis. These tracks differ not only in their moisture characteristics but also in their dominant energy conversion pathways and vertical structure, with southern-track waves more barotropic at jet level and driven substantially by latent heat release from deep convection.
A central question in AEW research has been whether the waves grow primarily from instabilities within the AEJ—the classical dynamical view established by National Hurricane Center forecaster Bob Burpee in 1972—or whether upscale forcing and diabatic heating from convection play an equally or more critical role. Our review argues that both mechanisms are complementary rather than competing. Landmark field campaigns including the 1974 GATE experiment, the 2006 NAMMA and AMMA campaigns, and the 2022 CPEX-CV mission have each advanced understanding of how convection and AEW dynamics interact across a range of scales. High-resolution kilometer-scale simulations have further revealed moisture–convection feedbacks that govern wave growth and propagation, and have identified some waves as potential moisture modes in which the wave is sustained by strong moisture gradients rather than purely by jet instability.
Our review also provides the first systematic comparison of AEW tracking methods, organized into a tracker family tree spanning spectral filtering, Hovmöller-based approaches, objective vortex tracking, and the most recent deep-learning techniques. A key finding is that most trackers show greater sensitivity to southern-track AEWs than northern-track AEWs, likely due to the stronger convective signals associated with the former. A companion summary table and online resource are provided to guide researchers in selecting the most appropriate tracking method for their applications.
Finally, our review addresses how AEW activity may respond to climate change. Historical reanalysis data since 1980 show a strengthening and poleward shift in AEW activity, and the increasing trend in Atlantic tropical cyclone frequency over this period has been linked specifically to storms with AEW origins. Future projections from both global and regional climate models—including convection-permitting simulations—broadly suggest further intensification of AEWs and enhanced associated rainfall in a warming climate, though disagreements remain across modeling frameworks.
The advent of convection-permitting models, AI-based tracking methods, and improved observing systems offer significant promise for resolving long-standing uncertainties about AEW initiation and growth, and its role in shaping tropical weather and climate variability. Our review aims to provide a clear-eyed view of current consensus, highlight key knowledge gaps, and serve as a foundational reference for the next generation of AEW research.
A Brief Conversation
with the Author
“When I was five years old, Hurricane Georges made landfall in Puerto Rico in 1998. I experienced it firsthand, and what started as a very real childhood fear gradually transformed into fascination. By the time I was in high school, I knew I wanted to study weather, specifically the storms that form in the tropics and the atmospheric systems that give rise to them. That little girl sheltering from Georges had no idea she’d one day be studying the African waves that spawn hurricanes like that one.”
—Kelly M. Núñez Ocasio, Texas A&M University
BAMS: What would you like readers to learn from this article?
Kelly Núñez Ocasio (Texas A&M University): We hope readers come away with a clearer picture of where the science stands on African Easterly Waves, from how they form and grow, to how they’re tracked, to how they may change in a warming climate. One of our central arguments is that the two leading theories of AEW growth—jet instability and upscale convective forcing—are not competing explanations but complementary ones, and we hope this review helps settle that debate. We also want this to serve as a practical resource: whether you’re a student encountering AEWs for the first time or a seasoned researcher looking for a synthesis of the tracking literature, we wanted there to be something useful here for everyone.
BAMS: How did you become interested in the topic of this article?
KNO: AEWs have been a central focus of my research since graduate school, they sit at the intersection of convection, tropical dynamics, and hurricane genesis, areas to which I have made significant contributions over the course of my career. Over time I kept noticing that there was no single resource that brought together everything we know about these waves. Researchers new to the field had to piece together decades of literature on their own. Writing this review felt like an opportunity to fill that gap and give the community the reference it deserved.
BAMS: What surprised you the most about the work you document in this article?
KNO: Honestly, the AEW tracker intercomparison was eye-opening. This is the first time we have systematically compared how different tracking methods perform against each other, and the differences were larger than we expected. Even for strong, well-defined waves, different trackers placed the wave center in noticeably different locations. We also found that virtually all trackers are more sensitive to southern-track AEWs than northern-track ones, a bias that has likely shaped our collective understanding of these waves in various ways.
BAMS: What was the biggest challenge you encountered while doing this work?
KNO: Synthesizing over 80 years of literature across observational, theoretical, and modeling studies was genuinely hard! AEW research spans so many subfields that even determining what counts as consensus versus ongoing debate required careful judgment. Bringing together a team of coauthors with complementary expertise was essential, and I’m deeply grateful for the collaborative effort that made this possible.
BAMS: How will you follow up this work?
KNO: This review has already informed several directions in my own research. I have papers examining how AEWs respond to a warming climate using convection-permitting simulations—a modeling approach that is only now becoming feasible for this kind of work. I’m also increasingly interested in how solar climate intervention might alter tropical atmospheric dynamics, including systems like AEWs. And I hope this review inspires others to tackle some of the knowledge gaps we identified, particularly around northern-track AEWs, observational coverage over Africa, and the role of AI-based tools in advancing our understanding of these fascinating systems.
- Key messages from “A Review of African Easterly Waves: Formation, Growth, Structure, and Evolution,” by Kelly Marie Nunez Ocasio (Texas A&M University), Quinton Lawton, Alan Brammer, Emily Bercos-Hickey, Stella Bourdin, Xiangbo Feng, Juliane Schwendike. Published online in the Journal of the Atmospheric Sciences, April 2026. ↩︎
