This year’s Saharan dust season made an early, dramatic arrival with a cloud believed to be the largest on record.
A dust cloud that started rolling off the African coast on June 15 began making it’s way over the Gulf of Mexico this week, causing air quality in North Florida and along the Texas coast to reach unhealthy levels. Sustained winds picking up dust helped feed the massive cloud, even as it began crossing the Atlantic.
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“It's not a one day pulse,” said Dale Griffin, a microbiologist with the U.S. Geological Survey. “It's a sustained event. It really shows you how small the world is and how connected we are on these atmospheric bridges that exist across vast expanses of oceans between continents."
The dust won’t likely be visible in South Florida, as winds push it south and carry it over the Gulf of Mexico. But it will be felt: the dust is wringing much of the moisture from South Florida’s wet season, the National Weather Service in Miami said.
Forecasters still can't model dust events in advance, so they can't say whether the dust season will be strong enough to knock down what's projected to be a busy hurricane season. The Atlantic basin has already churned up three named storms this year.
COVID-19 is also compounding respiratory concerns, especially with the virus surging in many places just as the dust arrives. The dust can worsen asthma and other respiratory issues. But doctors say the virus is too new to know whether the dust will worsen symptoms. Mask requirements in many places, however, may actually help stop irritation from the dust.
The dust season typically occurs between July and August, just before hurricane season begins to peak, Griffin said. Timed right, the dust clouds can help weaken storms even when other conditions are ripe. But forecasters can’t yet model the dust season, like they do for hurricanes, and forecast when they will occur.
“We have some [models] that do short forecasts and do back forecasts looking at where the air masses come from,” Griffin said. “But nothing like the kind that are utilized for the hurricanes. I think we'll get there eventually. I don't think scientifically we're quite there yet.”
Every year, Saharan dust clouds move about 4 million tons of dirt across the Atlantic, he said. That can be a good thing: the iron-rich clouds helped create the fertile Redland soil in Miami-Dade where much of the nation’s winter tomatoes are grown. They also help fertilize the Amazon.
But Griffin, who began his career two decades ago studying a cloud the size of Spain, said they also carry pathogens that can sicken plants and animals. They also seed red tides in the Gulf of Mexico and feed bacteria that can contaminate the Gulf’s vast oyster beds.
“We are really just beginning to understand not only the beneficial effects, but those that may present risks to crops, plant pathogens, livestock and wildlife. We found a pathogen in Mali that was heading west toward the ocean that was a pathogen for the loggerhead turtle,” he said “They're really biologically alive, these clouds.”
While the region monitors for pollution from land, he says monitoring needs to expand upward.
“We have a great shellfish harvesting alert system in Apalachicola. But that's based typically on rainfall that drives land-based sources of pollution driven by precipitation that come down in the harvesting regions,” he said. “What nobody is looking at is the sky.”
