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Saharan dust clouds blanket Florida and the Atlantic coast. How does it affect weather?

·4 min read

Noticing hazy skies in Florida?

That could be dust carried from Africa's Sahara Desert, making it all the way to the Southeast states.

The movement of dry air filled with Saharan dust happens yearly, often reaching the United States just before the Atlantic hurricane season.

Along with air pollution, other possible health hazards include eye, ear, nose and throat irritations.

Treasure Coast fishing: Ignore Saharan dust; Tarpon, snapper still biting for anglers

How does Saharan dust affect weather?: Saharan dust clouds reached Florida and the Atlantic coast.

NASA research split: Will Florida see more or less of these yearly storms?

See Thursday's dust forecast below from NASA and the Global Modeling and Assimilation Office (GMAO), an organization that uses computer models and data assimilation techniques to enhance NASA’s program of Earth Observations.

What is Saharan dust?

Also called the Saharan Air Layer (SAL) by the National Oceanic and Atmospheric Administration, Saharan dust is a mass of very dry, dusty air that forms over the Sahara Desert during the late spring, summer and early fall.

Its dust clouds can travel and impact locations around the globe, thousands of miles away from its African origins. The warmth, dryness and strong winds associated with the dust clouds have been shown to suppress tropical cyclones.

"SAL activity typically ramps up in mid-June and peaks from late June to mid-August, with new outbreaks occurring every three to five days," Principal Investigator Dr. Jason Dunion, a University of Miami hurricane researcher, said.

"During this peak period, it is common for individual SAL outbreaks to reach farther to the west — as far west as Florida, Central America and even Texas — and cover extensive areas of the Atlantic."

How does the SAL influence weather and climate?

According to the National Weather Service, there are three characteristics of these Saharan dust outbreaks that can affect tropical cyclones, tropical disturbances, and the general climatology of the Atlantic tropical atmosphere:

  1. Extremely Dry Air: The Saharan Air Layer’s dry, dusty air has about 50% less moisture than the typical tropical atmosphere. This extremely dry air can weaken a tropical cyclone or tropical disturbance by promoting downdrafts around the storm.

  2. African Easterly Jet: Strong winds in the Saharan Air Layer (25-55 mph or 10-25 meters per second) can substantially increase the vertical wind shear in and around the storm environment. This “mid-level jet” of enhanced winds, typically found at a height of 6,500-14,500 feet (2000-4500 meters), can cause tilting of the tropical cyclone vortex with height and can disrupt the storm’s internal heat engine.

  3. Warm Temperatures: The Saharan Air Layer’s warmth acts to stabilize the atmosphere, which can suppress the formation of clouds. This stabilizing effect is produced when the Saharan Air Layer’s warm, buoyant air rides above relatively cooler, denser air. The Saharan Air Layer’s suspended mineral dust also absorbs sunlight, which helps maintain its warmth as it crosses the Atlantic Ocean.

Saharan dust has vibrant sunsets

In short terms... Because of the special way Saharan dust scatters sunlight, the best times of day to spot it are usually a few hours after sunrise and in the late afternoon, according to the SAL website. During the day, the sky will have a hazy white look and sunsets will take on an orange glow.

In long terms... The sun's white light is composed of all the colors of the rainbow. Our skies are normally blue because the gases that make up the atmosphere naturally scatter blue hues (shorter wavelengths) as opposed to the yellow-orange-red hues (longer wavelengths). Sunsets and sunrises take on more yellow and reddish hues because the low-angle sunlight passes through more of the atmosphere before it reaches your eyes. A heavy load of dust in the atmosphere can enhance this effect, leading to longer-lasting, duskier colors that cause vivid sunsets and sunrises.

What to expect the rest of August

“Quite a bit” of Saharan dust comes across the Atlantic around this time of year, according to Brendan Schaper, a meteorologist with the National Weather Service in Melbourne, Florida.

“It can continue. Right now we're seeing a decent plume across the tropical Atlantic,” Schaper said. “And that may continue for the next couple of weeks, depending on the flow off of the coast of Africa.”

He said activity in the tropics will “determine the strength and nature of where that layer actually kind of goes.”

In terms of the Treasure Coast, Schaper said, rain chances are expected to increase over the weekend.

“We've got around 50% there on Saturday, and then on Sunday going up into the 60% and 70% range,” he said. “We do expect a kind of a moistening of the atmosphere in general across East Central Florida this weekend.”

He said there is nothing on the radar in the near future in terms of storms.

Grace Pateras is a digital producer for the USA TODAY Network. Follow her on Twitter at @gracepateras.

Will Greenlee is a breaking news reporter for TCPalm. Follow Will on Twitter @OffTheBeatTweet or reach him by phone at 772-267-7926. E-mail him at will.greenlee@tcpalm.com

This article originally appeared on Treasure Coast Newspapers: Saharan dust clouds blanket Florida and the Atlantic Coast. What is it?