(USA TODAY) -- Airlines have already canceled more than 3,000 flights because of Hurricane Sandy, which is not expected to make landfall until sometime tomorrow.
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Flight-tracking company FlightAware.com says 707 U.S. flights have been canceled already today (Oct. 28), with the highest number coming at Newark Liberty airport - a major hub for United.
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Monday's flight schedule has taken a bigger hit, with the tally of preemptive cancellations at 2,499 as of early Sunday morning, according to FlightAware.
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"Most affected is Newark (EWR), with 774 cancellations, second is Dulles with 428 cancellations, third is Philadelphia with 355 cancellations," FlightAware says in a statement.
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The flight-tracking agency warned of widespread flight disruptions and said the number of preemptive cancellations could "rise considerably throughout the day."
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"Although most air traffic control towers will close when the wind reaches 60-70 knots, the big factor that will result in early flight disruptions is mass transit shutdowns and the availability of airline and airport staff due to their need to prepare for the storm," FlightAware CEO Daniel Baker says in a statement, noting that New York's mass transit agency plans to halt train service around 7 p.m. this evening.
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United Airlines became the first carrier to publicly announce it would begin paring flights ahead of Sandy.
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United announced this morning (Oct. 28) it already has started canceling "selected flights to and from mid-Atlantic and northeast airports beginning Sunday evening."
Starting on Monday, United says it will "limit or suspend service" to nearly 30 airports in the region, including at two of its busiest hubs: Newark Liberty and Washington Dulles. United adds that it "expects to resume service on Tuesday with selected cancellations, weather permitting."
"Based on the forecast, today (Sunday) we will likely suspend operations scheduled for tonight and tomorrow at several airports in the region," United spokesman Rahsaan Johnson tells Today in the Sky. "Conditions are likely to keep us from operating with an acceptable margin of safety."
"Some of the cancellations begin this evening -- as opposed to tomorrow -- because we want to ensure we get airplanes out of the path of the storm to minimize disruption for customers outside the region," Rahsaan adds. "We don't want to inconvenience customers flying from, say, Los Angeles to San Francisco, because their airplane is stuck on the East Coast."
FlightAware says its flight data shows that United plans to halt its flight operations between 6 p.m. and 8 p.m . ET tonight at Washington Dulles, Philadelphia and the three New York City-area airports (Newark Liberty, LaGuardia and JFK).
FlightAware says it appears United's flights will remain suspended at those airports - which include its two major East Coast hubs at Newark and Dulles - at least through Tuesday afternoon.
FlightAware CEO Baker predicts other airlines will follow a similar course.
"US Airways will announce their cancellation schedule at noon today although their regional carrier, Air Wisconsin, has already cancelled flights on Monday at PHL (Philadelphia) and (Washington National) DCA.," Baker says in FligthtAware's statement. "JetBlue is also deciding later pending determination of staffing availability."
Last year, more than 14,000 flights were canceled over a four-day period last year when Hurricane Irene and its remnants tracked over the mid-Atlantic and Northeast.
Sandy is expected to make landfall sometime Monday, but the storm's is currently forecast to bring hurricane or tropical storm conditions to a large swatch of the region for up to 72 hours, according to forecasts.
Besides the airlines, Amtrak has already canceled about a half-dozen train runs on Sunday and Monday. The rail carrier warned more were possible as Sandy nears.
Back to skies, every big U.S. airline -- including American, Delta, JetBlue, Spirit, Unitedand US Airways -- has issued flexible travel policies that allow fee-free changes for many passengers ticketed to fly to the Northeast and mid-Atlantic during the next few days.
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Looking ahead, major delays and waves of cancellations are possible as the next work week begins.
Sandy is forecast to push heavy rains into much of the large swaths of the Northeast by Monday. The storm's center is likely to make landfall somewhere along the New Jersey or Delaware coast late Monday, according to computer forecasting models looked at by USA TODAY.
One thing that now appears certain: Sandy is expected to pass over or near some of the nation's busiest and most delay-prone major airports, and strong winds could begin buffeting airports by late Sunday.
Among them: New York JFK, Newark Liberty, New York LaGuardia, Philadelphia, Washington Dulles, Washington Reagan National, Baltimore/Washington and - possibly - Boston.
Nearly every major U.S. airline has at least one hub or "focus city" among those airports. Several have two, such as United (Newark and Washington Dulles), US Airways (Philadelphia and Washington National) and JetBlue (New York JFK and Boston).
Even a moderate disruption of those airports could affect thousands of flights and tens of thousands of passengers. An outright suspension of flights at a combination of those airports would wreak havoc that could spread throughout the U.S. aviation grid and create a backlog of stranded fliers that takes days to clear.