https://phys.org/news/2018-07-sahara-storm-killer.html

Texas A&M's Bowen Pan, Tim Logan, and Renyi Zhang in the Department of Atmospheric Sciences analyzed recent NASA satellite images and computer models and said the Saharan dust is composed of sand and other mineral particles that are swept up in air currents and pushed over the Atlantic Ocean to the Gulf of Mexico and other nearby regions.

As the dust-laden air moves, it creates a temperature inversion which in turn tends to prevent cloud—and eventually—storm formation.