A plume of Saharan dust is moving toward Houston. Here's how it happens.

Dust from the hot sands of the world's largest desert is making its way to Houston once again.

Each summer, massive plumes of dust from the Sahara in North Africa travel thousands of miles across the Atlantic before reaching Texas. The phenomenon can turn Houston's skies hazy, worsen air quality for some residents, create vivid sunsets and even influence weather patterns during hurricane season.

The arrival of Saharan dust is a regular part of summer weather along the Texas Gulf Coast, and at least one plume is expected to reach Southeast Texas in the coming days.

How does dust from Africa reach Texas?

The Sahara produces an estimated 400 million to 700 million tons of dust each year, making it the world's largest source of airborne mineral dust.

The strongest dust outbreaks are often triggered by thunderstorm complexes over the Sahel region south of the Sahara. As thunderstorms collapse, they produce powerful outflow winds that sweep across the desert floor, lifting enormous amounts of dust into the atmosphere. The dust then becomes trapped within the Saharan Air Layer, where it is carried westward across the Atlantic.

Pushed westward by prevailing easterly winds, the dust can travel thousands of miles across the tropical Atlantic Ocean, reaching the Caribbean Sea, the Gulf of Mexico and the southern United States.

Many of the largest plumes can be seen from space and tracked by satellites as they move toward Texas.

How does Saharan dust affect Houston?

For most Houstonians, the first sign of a Saharan dust plume is a hazy sky.

When dust concentrations increase, the atmosphere can take on a whitish or milky appearance, even on otherwise sunny days. Visibility can occasionally be reduced, although the effects are usually less dramatic in Houston than in parts of the Caribbean or South Florida, where dust concentrations can be higher.

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The same process can also produce especially vivid sunrises and sunsets, with shades of orange, red and pink appearing more intense than usual.

Does Saharan dust affect hurricanes?

Saharan dust season overlaps with the Atlantic hurricane season, which runs from June 1 through Nov. 30.

The Saharan Air Layer is typically hot, dry and often accompanied by stronger winds higher in the atmosphere. Those conditions can suppress cloud formation and thunderstorm development while also making it more difficult for tropical disturbances to organize and strengthen into tropical storms or hurricanes.

While Saharan dust does not prevent hurricanes from forming, large dust outbreaks can temporarily suppress tropical development across portions of the Atlantic Ocean. Dust outbreaks also tend to become less frequent later in the summer, allowing tropical waves emerging from Africa to move through a more favorable environment during the peak of hurricane season, which typically runs from mid-August through mid-October.

That's why periods with extensive Saharan dust are often viewed as one factor that can slow tropical activity, at least in the short term.

Does Saharan dust affect Houston air quality?

It can, but usually only during particularly intense Saharan dust outbreaks.

The dust contains tiny particles that can increase levels of particulate matter in the air. While most people experience few if any effects, those with asthma, chronic obstructive pulmonary disease, allergies or other respiratory conditions might experience irritation, including a scratchy throat, coughing, sneezing, a runny nose, eye irritation and worsening asthma symptoms.

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People who are sensitive to air pollution might want to monitor air quality forecasts from the Texas Commission on Environmental Quality and limit prolonged outdoor activity when dust levels are elevated.

When is Saharan dust season?

The most active period typically runs from late spring through early fall, with June and July often producing the largest dust outbreaks.

Along the Texas Gulf Coast, some of the season's first notable dust plumes typically arrive in late June before more waves move through during July and August. Because of that timing, Saharan dust often becomes a topic of conversation in Houston as summer and hurricane season begins in earnest.

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