U.S. airlines will cancel at least 6,100 flights over the next three days, grounding hundreds of thousands of passengers as Hurricane Irene sweeps up the East Coast.

If weather forecasters are right, the storm could strike major airports from Washington to Boston, buffeting them with heavy rain and dangerous winds.

United Continental Holdings Inc., the world’s largest airline company, said late Friday it would cancel 2,300 flights Saturday and Sunday. Delta Air Lines said it would shut down entirely at New York-area airports on Sunday and cancel 1,300 flights through Monday.

US Airways canceled 1,166 flights for Saturday and Sunday, JetBlue Airways scrubbed about 880 flights through Monday, and AirTran Airways, owned by Southwest Airlines, also canceled 265 flights through Monday. American Airlines said it would cancel 265 flights on Saturday and probably even more on Sunday.

American expected to halt flights in and out of Washington-area airports around noon Saturday, but United hoped to remain open at Dulles International Airport in suburban Virginia, said spokesman Mike Trevino.

The hurricane is expected to make landfall around North Carolina on Saturday, move up the coast to New York on Sunday and then weaken in New England.

Delta’s 1,300 cancelations, including Delta Connection flights, will equal about 8 percent of the company’s flights between Saturday and Monday.

Many of the cancelations were on smaller, so-called regional affiliates such as United Express, Continental Express and Delta Connection. When weather limits flights at an airport, airlines ground those smaller planes first and try to salvage flights on the bigger "mainline" jets.

The airlines declined to say how many passengers would be affected by the hurricane, and the mix of small and big planes made it hard to estimate a figure. But the JetBlue flights, mostly on one type of aircraft, would likely have carried about 110,000 passengers, and they’ll account for only about 15 percent of all canceled flights.

Airlines waived rebooking fees for customers who wanted to delay their flights to more than two dozen cities on the East Coast. Details varied by airline, with some giving travelers more time to make their rescheduled flight. Travelers whose flights were canceled would be eligible for refunds.

George Hobica, founder of the travel website airfarewatchdog.com, said travelers who bought nonrefundable tickets should wait until the airline cancels the flight rather than taking the airlines’ offer to reschedule by a few days.

The problem with rebooking on the airlines’ terms, Hobica says, is that you’re unlikely to want to take the same trip a few days later.

Airlines have reduced flights in recent years, meaning it could be several days for stranded travelers to find a seat on another plane, says Airline consultant Mark Kiefer.

The hurricane will also affect cars, buses and trains.

A spokesman said Greyhound Lines started to cancel some service between Washington and New York on Thursday. Amtrak canceled most of its scheduled Saturday passenger rail service through Sunday south of Washington.