Airlines began to cancel flights and get planes out of the way as Hurricane Irene barreled toward the U.S. mainland on Thursday.
The storm will likely force hundreds of flights to be cancelled through this weekend and create delays that could ripple across the country.
Airlines said passengers could rebook those trips to many East Coast destinations, from Boston to the Carolinas, for free.
As of late Thursday afternoon there were nearly 900 cancellations into, out of, or within the United States, with the majority concentrated at New York's three major airports, along with Philadelphia and Miami. Although not all cancellations were a result of Irene, that figure was several times greater than the number of cancellations on a typical day.
American Airlines and its American Eagle affiliate, with an extensive network in the Caribbean, canceled 126 flights on Thursday. Most were in the Bahamas and south Florida, including Miami, a jumping-off spot for flights to the Caribbean and Latin America.
Even before Irene's arrival, unrelated thunderstorms were causing delays of up to two hours Thursday at major airports in the New York and Washington areas, according to flight-tracking service FlightAware. The service's CEO, Daniel Baker, predicted that Irene-related cancelations would pick up Friday afternoon and become significant on Saturday, when the storm is expected to come ashore in North Carolina.
The airlines' preparation reflects a new approach to dealing with big storms. In recent years, they have waived ticket-change fees and canceled flights long before storms arrive. That has helped reduce the number of travelers and flight crews who get stranded at airports. Canceling flights ahead of time keeps planes out of the path of damaging storms and lets airlines resume normal schedules more quickly after the bad weather passes.
But sheltering planes far from a storm carries risks. If the storm changes path and misses big airports, hundreds of flights will have been canceled unnecessarily.
Irene presents another challenge. Because major travel hubs such as Washington and New York are in its potential path, flights that are canceled or delayed there tend to ripple across the country.
"Most everyone expects New York to get hit, so you're obviously not going to leave a lot of planes on the ground in New York, waiting for a problem," said Tim Smith, a spokesman for American Airlines.
He said all the airline's Thursday flights in the Bahamian capital of Nassau were canceled and there were delays in Miami due to heavy rain. He said the airline would track forecasts before making decisions about cancelations for Friday.
The airlines announced policies for changing trips free of the normal ticket-change charges.
Travelers on American going to 14 cities from Boston to Raleigh-Durham, N.C., could delay trips as late as Sept. 7 without penalty. Policies on Delta and United Continental were more restrictive at midday Thursday.
The offers were too late for some travelers whose long-planned trips turned soggy.
Noelia Chacon of Spain, touring the East Coast with her husband and son, were evacuated from the Smithsonian in Washington after Tuesday's earthquake and now might limit their New York sightseeing because of Irene. Their tickets and hotel in Newark, N.J., are nonrefundable.
"We've had an earthquake and a hurricane so far. We'll see what's next," Chacon said, as rain fogged the windows of the hotel lobby. "This is a trip we will not soon forget."