Saharan dust — and its dry air — may help suppress hurricanes, for now

Don't get out your Swiffer, but there's a whole heap of dust headed our way from Africa. The dust, which originates in the Sahara Desert, is going to help Florida dodge tropical storms at the start of hurricane season.

The National Oceanic and Atmospheric Administration calls it the "Saharan Air Layer." It can extend 5,000 to 20,000 feet above the earth.

The dust brings with it a mass of dry air, explained Michael Brennan of the National Hurricane Center in Miami, which "tends to suppress any tropical cyclone development."

Tropical storms and hurricanes need warm, moist air to form, he explained. The dust plume's dry air evicts all the moisture and thus robs potential storms of the fuel they need to start spinning our way.

The tiny particles in the Saharan Air Layer have a surprisingly large impact on the weather in this part of the globe, showing what a complicated mechanism the earth's weather patterns can be.

At least half of the dust originates in a dry lake bed in north central Chad, near the Sahara's southern end. The lake bed is known as the Bodélé depression. It used to be part of a larger water body called Lake Chad.

In the mid-1960s, Lake Chad was about the size of Lake Erie. But persistent droughts coupled with increased freshwater use for irrigation reduced Lake Chad to about 5 percent of its original size. Now it's just a repository for the skeletons of microscopic creatures that once lived in the lake. That's what forms the dust.

Every year, over about 100 days from spring to the fall, a scouring wind blows between a gap in the mountains just upwind of the depression, forcing it to accelerate to a speed that will pick up the tiny particles and carry them thousands of miles across the Atlantic Ocean. The tiny bits float along on the wind, soaring up to 3 miles above the surface of the water. Sometimes they clump together into a hazy configuration as large as the continental United States.

Then they land at last in and around the Caribbean Sea and the Gulf of Mexico.

Usually the dust particles feed phytoplankton, build Caribbean beaches and fertilize the Amazonian rain forest.

Sometimes the dust creates beautiful sunsets. Sometimes it causes a thick haze to hang in the air over Texas. And sometimes, scientists say, it can feed toxic Red Tide algae blooms like the recent one off Florida that lasted 14 months.

The most recent plume of Saharan dust was first spotted by satellites floating above Africa on Father's Day, and began arriving in the Gulf of Mexico this past weekend. Scientists were quick to caution weather watchers that a dust plume now does not affect what the hurricane season may be like later in the year. The strongest storms form later: August, September and October account for 93 percent of Category 3 or stronger hurricanes in the Atlantic.