Another storm is headed toward South Florida -- and it's not a hurricane.

Born in the desert of North Africa, an immense cloud of Saharan sand is being swept across the Atlantic Ocean by the tradewinds. By early next week, South Floridians will experience hazy blue skies, bright orange sunsets and coats of reddish dust on their cars, the National Weather Service said Friday.

''This is not going to be a tremendous event, but it will be kind of interesting,'' said Jim Lushine, a severe weather expert with Miami's weather bureau.

The sand is lifted from the Sahara Desert, piggybacking on the tropical waves that sweep from east to west over the Atlantic. Such dust clouds are fairly common in July and August, although they can vary in intensity from year to year.

''It's really not rare,'' said Joseph M. Prospero, a professor at the University of Miami's Rosenstiel School of Marine and Atmospheric Science. ``We normally see several extreme dust events each year.''

Air quality is expected to worsen a bit, although experts say the dust shouldn't pose any serious health problems. As a precaution, people with breathing problems may want to limit their time outdoors, said Jim Wheeler, a supervisor with the air monitoring division of the Miami-Dade County Department of Environmental Resource Management.

''Most of it is going to be in the upper atmosphere,'' Wheeler said.

This particular cloud will likely affect the Caribbean basin more directly, and linger over the region for about 12 hours. It measures about 1,500 miles north to south and 2,500 miles west to east.

''About the dimensions of the lower 48 states,'' Lushine said.

Because the Sahara dust carries some pathogens, it might cause harm to coral reefs, particularly in the Caribbean, said Bernhard Riegl, an associate professor at Nova Southeastern University's Oceanographic Center. Those pathogens, he said, include fungi, spores and bacteria, but the dust can haul even bigger objects. "Entire desert locusts, the insects, have made it across the Atlantic to the Windward Islands."

So far, there is no evidence the pathogens harm humans, although on the Caribbean island of Trinidad an abnormal number of infants have asthma problems, he said.