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Dust in the wind: How the Sahara Desert factors into tropical action

Saharan Air Layer effects on a tropical disturbance (2024)
Posted at 6:54 PM, Jul 08, 2024

TALLAHASSEE, Fla. (WTXL) — Tropical storms and hurricanes depends on, among other things, high amounts of moisture in the atmosphere to build and sustain strength. But there are times in the hurricane season when nature zaps away the moisture and keeps activity low.

Airborne dust from the vast deserts on the African continent often contribute to settled periods in the Atlantic Ocean and other nearby waters, limiting the growth of tropical systems.

"How does the desert dust becomes airborne?" you might wonder. Tropical waves — clusters of moisture around an area of low pressure — originate over land near the Saharan region of Africa. The wind forces from the disturbances lift the dust higher into the atmosphere, and mid- and upper-level winds keep the mineral-rich mass flowing aloft. This dry air source emerges from the Sahara Desert in the warmer times of year and spreads over parts of the Atlantic basin, following natural air flows in the atmosphere. The layer of dry, dusty air is usually about one to two miles thick, and located about one mile above the Earth's surface.

Amounts of dusty air tend are common in the first few months of the Atlantic hurricane season. While the amounts can vary between light amounts to dense, the layers tend to reach their peak from June to mid-August, and can travel across the expanse of the Atlantic basin waters during these months.

The combination of decreased moisture, stronger wind aloft, and warm air acts to decrease tropical storm development in the open Atlantic. The plume of dust can reach the mainland United States, also cutting down formation efforts in the Gulf of Mexico.

During the times that the Saharan air layer does reach land, including the Big Bend and southern Georgia, the Saharan dust can create a hazy appearance to the daytime sky, and add red hues to the setting and rising sun. People with sensitive respiratory systems or related ailments can experience breathing difficulties which the dusty layer is particularly dense and thick.

Tropical systems require that deep moisture source to maintain and gain strength. A disturbance embedded in the dust zone ingests that drier air into its circulation, effectively decreasing available moisture in its core and causing a weakening trend in the disturbance. Such was the case before the July 4th holiday weekend when a tropical wave in the lower North Atlantic had a reasonable chance to develop more, but it got caught up in the Saharan air layer and dwindled in organization as it reached the Caribbean Sea.

There are occasions — like with the recent Hurricane Beryl — that tropical waves and the deep moisture they carry can travel just outside the periphery of a Saharan dust zone. The upper-level wind pattern along the edge can actually lend support to a storm system trying to develop while not getting the actual dry air caught up in its circulation.