Big airports in Florida remain closed, and flight cancellations are spreading north along the track of Tropical Storm Irma.
American Airlines said it won't resume flights in Miami until at least Tuesday, revising its plans to restart late Monday.
An airline spokesman says the timetable depends on approval by federal aviation officials and the ability of security screeners and airport vendors to return to work.
More than 3,800 U.S. flights scheduled for Monday were canceled by late morning -- and more than 9,000 since Saturday -- according to tracking service FlightAware.
Disruptions have spread beyond Florida. Delta Air Lines is canceling 900 flights Monday, including many at its Atlanta hub because of high winds. American is canceling 300 flights in Charlotte, North Carolina, due to wind.