COLUMBUS (WCMH) — The vast plume of dust that originated over the African continent June 7 reached the Gulf Coast states Thursday, after traveling more than 5,000 miles across the Atlantic, Caribbean and Gulf of Mexico.
The east-to-west trajectory of the hazy coloration on satellite imagery is driven by easterly trade winds that flow in the tropics. The African Easterly Jet, at a higher altitude, was weaker than usual in June, which allowed more dust to accumulate that is generated by thunderstorms. Storm outflow produced large swaths of dust over the Sahara Desert that were drawn up into the atmosphere and transported westward by the upper-level winds.
Modern satellite records over the past 15 years indicate this is the thickest Saharan Air Layer (SAL) ever tracked across the tropical Atlantic. The visibility in Puerto Rico dipped to 3 miles Wednesday, dimming the sky in a soupy gray haze. Regional meteorologists believe this is the most extensive dust cloud in the past 50 years.
Where to expect the dust plume
High pressure off the southeastern U.S. will direct the plume of dust northward into the southern states early in the weekend. Large clusters of thunderstorms moving inland from the Gulf could mitigate some of the health impacts by washing out the air. Locally, 7 to 9 inches of rain fell in southeastern Texas and southern Louisiana.
Residents of Louisiana, Alabama, Georgia and Florida will experience a milky sky or brownish haze and a decrease in air quality. A second surge of dust will spread northward up the Mississippi River valley and spill eastward as far north as Ohio, but denser concentrations will remain over the Southeastern states.
Optical effects of a dust in upper atmosphere
Dust plumes reaching the U.S. are not unusual, but normally most of the residue settles to the ground. The dust particles are slightly larger than oxygen and nitrogen molecules in the air that effectively scatter sunlight, taking out most of the shorter-wavelength blue, while creating red-tinged sunrises and sunsets. At these times, when the sun is at a low angle and sunlight passes through a deeper layer of the atmosphere, scattering and refraction of sunlight are maximized.
One impact of the Saharan Air Layer is to limit hurricane development in the Atlantic Basin because the air is sinking and drying. Incipient tropical systems that ingest dusty air tend to weaken quickly, although tropical easterly waves with accompanying clusters of thunderstorms can survive reasonably well over the open waters of the Atlantic.