At a Glance

A large swirl of low pressure is expected to form over Central America.These "gyres" often trigger dangerous, life threatening flooding there.Sometimes, these large gyres can also spawn tropical depressions and storms.The chance for that to happen in the Caribbean Sea appears very low, for several reasons.

Weeks before the 2022 Atlantic hurricane season's official start, a low-pressure system may bring flooding rain to Central America, but it likely won't spawn the first tropical depression or storm in the Caribbean Sea.

We understand if this might catch you a little off guard; It's only May. There's a scenario setting up that can sometimes lead to tropical development in the Caribbean Sea, but likely not this time.

First, a large, broad area of low pressure is expected to form in the next few days over Central America, something meteorologists refer to as a Central American gyre, or CAG.

These CAGs most often form from , but can occur at any time over the next six months.

Why CAGs Matter For Development

These CAGs can spawn or influence tropical storms in the Caribbean Sea, Gulf of Mexico or eastern Pacific Ocean.

Two years ago, one such CAG also formed in late May.

It pushed eastern Pacific Tropical Storm Amanda inland into Guatemala, then steered its remnant into the Bay of Campeche, where soon formed. The CAG forced Cristobal to make a weird loop over southeast Mexico before Cristobal finally turned north toward a Gulf Coast landfall on June 7, 2020.

Roughly 50 percent of CAGs have a tropical cyclone associated with them, Philippe Papin, a hurricane specialist at the National Hurricane Center and expert on CAGs, previously told weather.com.

"When a tropical cyclone does occur, it tends to form on the eastern side of the [gyre] and rotates counterclockwise around the larger circulation," said Papin.

That's what one prominent computer forecast model – the Global Forecast System (GFS) – had been suggesting could happen in its various updates since late last week.

While that sounds a bit unsettling, there were problems with that model's forecast.

First, while the GFS model can detect tropical storm formations in the western Caribbean Sea, it . That means this particular model will often forecast tropical development that doesn't end up happening.

Other forecast models, such as one from the European Centre for Medium-Range Weather Forecasts (ECMWF), suggest the CAG could be centered farther west over Central America or the eastern Pacific Ocean, making development chances higher in the eastern Pacific Ocean than over the Caribbean Sea.

And more recent GFS model forecast runs have now it had been previously forecasting.

Even if a tropical depression could form in the Caribbean Sea, it would face two other obstacles.

First, wind shear in the Gulf of Mexico and northwest Caribbean Sea is strong, as you'd expect in May. This changing wind speed and direction with height typically rips apart tropical disturbances trying to organize.

Current Wind Shear

(Areas of clouds are shown in white. Areas of strong wind shear, the difference in wind speed and direction with height, are shown in purple. High wind shear is hostile to mature tropical cyclones and those trying to develop.)

Secondly, there's a push of air originating from the Sahara Desert headed through the Caribbean Sea over the next few days.

Known as a Saharan Air Layer (SAL), these westward surges of dry, stable, dust-laden air suppress thunderstorms, the building blocks needed to form a tropical depression. Some of this air may be in place over the western Caribbean Sea into the weekend.

Water Vapor Satellite Image

(Areas of drier air are shown as darker orange and red. Areas of deeper moisture are shown in the white to purple to green shading. In this case, drier air is pushing into the Caribbean Sea from a Saharan Air Layer. )

The bottom line is we're not concerned in this case about a tropical depression or storm forming in the Caribbean Sea in this setup.

Dangerous Flood Threat Regardless

As the large low sits over or near Central America, it could wrap deep moisture into areas from southeast Mexico to Panama into next week.

Some areas could pick up over 6 inches of rain, particularly over windward mountainous terrain.

That could lead to life-threatening flash floods and mudslides.

Rainfall Potential

(This should be interpreted as a broad outlook of where the heaviest rain may fall. Higher amounts may occur where bands of rain stall over a period of a few hours, particularly near higher terrain.)

CAGs have been notorious flash flood producers, often with deadly results.

The combination of Amanda, Cristobal and the CAG over nine days dumped up to 34 inches of rain in southeast Mexico, 42 inches in El Salvador and 26 inches in Guatemala. Forty-three deaths were attributed to the flooding or landslides in Central America.

In early October 2017, a CAG spawned , which made a Category 1 landfall along the Mississippi Gulf Coast.

But the early stage of Nate as a tropical depression and storm, combined with the CAG, soaked Central America. Some parts of Costa Rica picked up 10 to 19 inches of rain.

Flooding and mudslides killed 44 people and destroyed thousands of homes, particularly in Costa Rica and Nicaragua, according to the National Hurricane Center's .

Flooding is seen in San Jose, Costa Rica, on Thursday, October 5, 2017, as Tropical Storm Nate brings dangerous torrential rains to the area.

(Twitter/@JorgeAlfaroCR)

In 2005, dissipated over the mountains of central Mexico, but its remnant spin became part of a larger gyre that triggered heavy rainfall over Central America.

While Stan's direct circulation resulted in about 80 deaths, severe flash flooding and mudslides from the gyre claimed an estimated 1,000 to 2,000 lives across Central America, according to the National Hurricane Center.

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