A thick cloud of dust from the Sahara Desert swept across the Caribbean on Monday, marking the largest event of its kind this year — and it’s now on a path toward the U.S.

Stretching nearly 2,000 miles from Jamaica past Barbados and 750 miles from the Turks and Caicos down to Trinidad and Tobago, the plume left skies hazy and residents sneezing across the region. Experts warn that the fine particles in the air could be especially harmful to those with asthma, allergies, or respiratory conditions.

“This one’s very impressive,” said AccuWeather’s lead hurricane expert, Alex DaSilva.

Puerto Rico’s National Weather Service reported the year’s highest dust concentration so far, with an aerosol optical depth of 0.55 — meaning a significant reduction in sunlight reaching the ground.

The plume is expected to reach parts of the southeastern U.S., including Florida, Louisiana, Alabama, and Mississippi, by the weekend. Health officials advise staying indoors or wearing masks if sensitive to dust.