Behind the Forecast: Saharan Dust’s Impact on the Atlantic Hurricane Season

LOUISVILLE, Ky. (WAVE) - Amid the Atlantic Hurricane season, all eyes are on the Atlantic basin and the African west coast. The dust drifting off Africa from the Saharan Desert can significantly impact hurricane season.

More than half of tropical storms and weak hurricanes that develop in the Atlantic originate off the North African coast. Around 85 percent of major Atlantic hurricanes come from Africa. For these storms to form and thrive, warm sea-surface temperatures, abundant water vapor, and unstable air are necessary.

The Saharan Air Layer (SAL) is a layer of dry, dusty air that develops over the Saharan Desert from late spring through the early fall. When tropical waves, which are ripples in the lower to middle atmosphere, track along the southern edge of the Saharan Desert, they throw incredible amounts of dust into the atmosphere. The Saharan Air Layer can be two to two-point-five miles thick in the atmosphere as it crosses the Atlantic Ocean. Its base typically starts around one mile above the surface.

The Saharan Air Layer is known to keep tropical cyclones from forming and strengthening. It can also travel thousands of miles from Africa’s west coast to the United States and Central America.

The Saharan Air Layer kicks into gear in mid-June, peaking from late June through mid-August. Outbreaks occur every three to five days. These outbreaks can be as large as the contiguous United States.

Meteorologists and researchers use infrared, visible, and water vapor satellite channels to track SALs as they traverse the ocean.

So why is Saharan dust detrimental to tropical cyclones?

There are three main reasons why the Saharan dust can be a death sentence for tropical systems.

First, the dry is exceptionally dry. The Saharan Dust Layer has around 50 percent less moisture than typical tropical air. The dry air can weaken a system by encouraging downdrafts (downward air currents) to form around a storm.

The Saharan Air Layer also has strong winds embedded within it. Winds of 25 to 55 MPH can increase vertical wind shear within and around a storm. The mid-level easterly jet’s strong winds are between 6,500 and 14,500 feet up in the atmosphere.

The warm, dry air of the SAL stabilizes the atmosphere, limiting cloud formation. The warm, buoyant SAL air sits above the cooler, dense air below - limiting convection. The Saharan dust absorbs plenty of sunlight, keeping that layer warm.

The Saharan Air Layer can limit storm formation when it reaches the U.S.; this can also help drive up high temperatures during the summer in areas under the SAL.

The Saharan Air Layer is something that we’ll have to continue to monitor throughout the rest of hurricane season.