Central American Gyre Could Trigger Dangerous Flooding; Could It Also Spawn Tropical Development? | The Weather Channel – Articles from The Weather…

Weeks before the 2022 Atlantic hurricane season's official start, a low-pressure system may bring flooding rain to Central America, but its chances of spawning the first tropical depression or storm in the Caribbean Sea are very low for now.

We understand if this might catch you a little off guard; It's only May. But there's a scenario setting up that can sometimes lead to tropical development.

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 May through June and again in October through November, but can occur at any time over the next six months.

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 Tropical Storm Cristobal 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) has been suggesting could happen.

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

First, while the GFS model can detect tropical storm formations in the western Caribbean Sea, it also has a high false alarm rate. 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.

Even in the small chance a tropical depression forms in the Caribbean Sea, it faces 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

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

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

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

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 Hurricane Nate, 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 final report.

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

In 2005, Hurricane Stan 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.

The Weather Companys primary journalistic mission is to report on breaking weather news, the environment and the importance of science to our lives. This story does not necessarily represent the position of our parent company, IBM.

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Central American Gyre Could Trigger Dangerous Flooding; Could It Also Spawn Tropical Development? | The Weather Channel - Articles from The Weather...