CENTRAL AMERICA — In September 2024, heavy rains exceeding eight inches fell on portions of Central America and southern Mexico. These rains resulted from a Central American Gyre that developed over Central America and adjacent waters. A lobe of this gyre over the northwestern Caribbean split off and developed into Hurricane Helene after three days, ultimately killing 217 people and causing $81 billion in damage.
The gyres are expansive areas of surface low pressure that typically take several days to organize and can persist for two weeks or more. They occur most frequently in May, June, September, October, and November. Approximately one-third of these gyres end up spawning a named storm. Between 1980 and 2010, 42 were classified, averaging approximately 1.4 per season, and spawned a total of 14 tropical cyclones.
In 2024, a gyre also spawned Tropical Storm Alberto, Hurricane Helene, and Hurricane Rafael. Hurricane Milton of 2024 was spawned by a tropical wave that interacted with the remnants of a gyre. The year 2024 shares the record for the most Atlantic named storms spawned by the gyres in a single year with 1998 and 2005.
La Niña events favor the formation of more gyres by weakening low-level easterly trade wind flow south of Central America. Hurricanes spawned by the gyres tend to be weaker than peak-season hurricanes due to cooler sea surface temperatures and higher wind shear. Philippe Papin, a National Hurricane Center hurricane forecaster, said, "It's likely that individual events will produce more rainfall due to higher moisture availability in a warmer atmosphere. As for changes in their overall frequency or duration, that remains an open question."
Papin also said, "If a warming planet shifts the Eastern Pacific Intertropical Convergence Zone more poleward, it could increase the risk of Central American Gyre events over Central America by enhancing moist southwesterly flow into the region, promoting elevated convection over higher terrain." A 2025 study noted that climate projections disagree on whether the intertropical convergence zone will expand, contract, intensify, weaken, shift location, or remain in place.