Saharan dust cloud heads toward Florida and may suppress storms
A plume of dusty air from the Sahara desert will sweep across southern Florida this week, suppressing storms, enhancing sunsets and threatening to worsen air pollution.
The dust cloud appears likely to smother a developing storm system heading toward the Caribbean from Africa, preventing it from strengthening into a tropical depression or anything more dangerous. And it could offer South Florida some protection against thunderstorms this weekend, as it arrives from its journey across the ocean.
“It’s been moving across the Atlantic for the past several days, and it’s expected to be in the area around Friday or Saturday,” said Sammy Hadi, meteorologist for the National Weather Service in Miami. “It acts to prevent widespread showers and thunderstorms. You could still have showers and thunderstorms, but the coverage would be much less if you didn’t have Saharan dust.”
The dust that could suppress storms over Miami, Pembroke Pines and Delray Beach rose thousands of miles away in strong winds that blew across desert regions of Mali and Mauritania, according to NASA, which monitors the plume with satellites. By June 7, a huge plume of dust was over the Atlantic and drifting west with the trade winds.
“It’s going to be substantial,” said Joseph Prospero, professor emeritus at the University of Miami’s Rosenstiel School of Marine and Atmospheric Science, who pioneered the study of the African dust clouds. “It’s going to be a major dust outbreak.”
Saharan dust chokes off infant hurricanes. The suppression of storms comes not from the dust itself but from the dry desert air that carries it. Hurricanes and tropical storms feed off humid tropical air, which rotates upward and forms the storms’ characteristic whirl of towering clouds. Dry air stops that upward movement, suppressing storm formation.
The National Hurricane Center is monitoring Tropical Storm Bill and two other patches of stormy weather that could develop into tropical cyclones, rotating storm systems that range in strength from tropical depression to hurricane.
One off the west African coast appears likely to run into the dry air of the Saharan dust cloud, limiting its chances to strengthen. But another off the Mexican coast has a 70% chance of forming a cyclone within the next five days.
There’s still uncertainly on the effect on South Florida’s weather, said Hadi, of the National Weather Service. It’s unclear how many days the dust will last. And the course of the storm system off Mexico is unclear. If that storm system forms a tropical cyclone and veer east of its expected course, South Florida could experience heavy rain, he said.
The dust’s arrival in Florida was first observed in the 1950s by Christian Junge, a German scientist who realized what he was looking at from his time in North Africa as a Luftwaffe meteorologist during World War II.
“He recognized it as African dust,” said Prospero, who worked with him. “And he looked at the meteorological charts and saw that the winds were right and there had been some dust storms in Africa about a week before.”
Since then, the phenomenon has been investigated by a growing corps of scientists who have studied its effect on climate, weather, marine biology and human health.
Saharan dust is a seasonal threat to South Florida’s air quality, which is generally good for an urban area. The Saharan air can cause milky, hazy conditions that can aggravate respiratory problems.
Monica Pognon, air quality chief for Broward County, said her office is monitoring the plume, which appears to be smaller than one that arrived last summer.
“We are watching it,” she said. “I don’t know if it’s going to have an impact on our air quality.”
If readings for particulate matter, which means small particles such as dust, scale into the unhealthy zone, she said the county would issue an alert advising people with respiratory problems to limit outdoor activities. But Saharan dust can come through without much impact on air quality, she said.
David Fleshler can be reached at dfleshler@sunsentinel.com and 954-356-4535.
