Forecasters at the National Hurricane Center say periods of heavy rain will continue across parts of Central America and southeastern Mexico through Saturday, September 26, raising the possibility of life-threatening flash flooding and landslides. The setup is a familiar one for this time of year: an elongated area of low pressure near the surface and deep tropical moisture parked over the region and neighboring seas.

In its Atlantic Tropical Weather Discussion issued at 0015 UTC on Thursday, September 24 (8:15 p.m. EDT Wednesday, September 23), the hurricane center said heavy rainfall looks likely across extreme southeastern Mexico near Chiapas, southern and central Guatemala, western Honduras, El Salvador, southern and eastern Belize, and parts of Costa Rica and Panama. Heavy rain was also falling from the waters northwest of Jamaica across the Cayman Islands and north across east-central Cuba to Andros Island in the Bahamas.

Setups like this often bring one term to social media every fall: the Central American Gyre. The hurricane center has not labeled this week's system a gyre, but understanding what gyres are helps explain why a broad weather system with no name and no hurricane-force winds can still be one of the most dangerous events of the season.

A Broad, Slow Spin Over Warm Water

A Central American Gyre, often shortened to CAG, is a large, closed, counterclockwise circulation of low pressure over Central America and nearby waters of the eastern Pacific, the Caribbean, and the southern Gulf. Unlike a hurricane, which is compact and organized, a gyre is broad, with its strongest winds spread over a wide region well away from the center.

A climatology of Central American Gyres by Philippe Papin, Lance Bosart, and Ryan Torn, published in Monthly Weather Review, identified 47 gyres from 1980 to 2010. The cases clustered in two peaks, May through June and September through November. The researchers found extreme rainfall over multiple days in every case they could examine, most often along the Central American coastline.

The danger comes from time and moisture. Gyres sit over some of the warmest water on the planet and move slowly, so the same mountains and valleys can be soaked day after day. In Central America's steep terrain, that repeated rain drives flash floods and landslides even when winds stay modest.

Storm Incubators on Either Coast

Gyres matter to hurricane forecasters because they can act as incubators. Smaller spins sometimes break away from the parent circulation and become tropical storms, either in the eastern Pacific or in the western Caribbean and southern Gulf.

The most notorious recent example came in September 2024. As meteorologist Jeff Masters wrote for Yale Climate Connections, a gyre dumped more than 8 inches of rain on parts of Central America and southern Mexico before a lobe over the northwestern Caribbean split off and became Hurricane Helene. The hurricane center's Hurricane Helene report confirms the storm originated from a gyre that developed on September 20, 2024. Masters noted, however, that only about one-third of Central American Gyres go on to spawn a named storm.

That caveat matters this week. As of the hurricane center's 8 p.m. EDT Tropical Weather Outlook on September 23, forecasters were not highlighting any area of possible development in the western Caribbean or southern Gulf. The only Atlantic disturbance they were monitoring for formation was far to the east, southeast of the Cabo Verde Islands off Africa. For now, the threat in Central America is heavy rain and flooding, not a developing storm.

This Week's Setup in Plain Terms

The hurricane center's discussion describes a mid- to upper-level trough stretching from the eastern Gulf across the Yucatán Peninsula and the northwestern Caribbean. An elongated low-level trough is expected to persist over the area for several days. Combined with warm sea surface temperatures and abundant low-level moisture, that pattern is funneling tropical moisture across Central America and the western Caribbean.

Forecasters said uncertainty remains about exactly where the heaviest rain will fall. That is common with broad systems, where small shifts in the circulation can move the heaviest bands from one valley to the next.

On the Pacific side, Hurricane Polo was an extremely dangerous Category 5 hurricane off southwestern Mexico, according to the hurricane center's latest public advisory on Hurricane Polo, issued at 9 p.m. CST on September 23. Polo is a separate, well-organized storm, but it underscores how active the eastern Pacific has been this season.

U.S. Weather and Travel Connections

For the United States, the effects are indirect. The hurricane center said an upper-level trough will support scattered showers and thunderstorms over the southeastern Gulf and the Straits of Florida for at least the next couple of days, and that a cold front is forecast to move into the northeastern Gulf Thursday night and Friday before stalling over the southeastern Gulf this weekend.

Travelers heading to Guatemala, Belize, Honduras, El Salvador, Costa Rica, Panama, or southern Mexico should expect possible flight delays, road closures, and landslide risk in mountainous areas. Families with relatives in the region may want to check in and share official warnings from national weather services.

Residents of the Gulf Coast and Florida do not need to take storm-specific action right now, but storms can still form close to U.S. shores in October. Checking the hurricane center's Tropical Weather Outlook, issued at least four times a day, is the simplest way to catch any change early.

Forecast Signals Worth Monitoring

Forecasters will be watching for a concentrated area of thunderstorms that persists over water and begins to show a defined center of circulation. If that happens, the hurricane center would add an outlook area with a formation probability, usually well before any watch or warning is issued.

In Central America, key warning signs include rapidly rising rivers, muddy runoff on hillsides, and cracks or bulges in slopes near roads and homes. Anyone in the affected areas should follow guidance from national civil protection and meteorological agencies, avoid crossing flooded roads, and move away from steep slopes during prolonged heavy rain.

The hurricane center's next discussions and outlooks will show whether the rainfall pattern shifts or whether any area begins to organize. For now, the threat is water rather than wind, and forecasters expect it to persist through Saturday.

What Readers Want to Know

What is a Central American Gyre?

It is a large, slow-turning area of low pressure over Central America and nearby waters, most common in May and June and from September through November, that can produce days of heavy rain.

Where is heavy rain expected this week?

The National Hurricane Center highlighted southeastern Mexico near Chiapas, Guatemala, western Honduras, El Salvador, Belize, and parts of Costa Rica and Panama through Saturday, September 26.

Is a tropical storm forming in the Caribbean?

As of the NHC outlook on the evening of September 23, forecasters were not monitoring any western Caribbean or Gulf area for development.

Can gyres produce hurricanes?

Yes. Hurricane Helene in 2024 formed from a lobe of a Central American Gyre, but only about one-third of gyres spawn a named storm.

Does this affect the United States?

Not directly. Scattered storms are expected over the southeastern Gulf and the Straits of Florida, and a cold front is forecast to stall over the southeastern Gulf this weekend.

What should travelers do?

Travelers to affected countries should monitor local weather services, expect possible delays, and avoid mountain roads during heavy rain.