The Federal Aviation Administration said late Monday it expected delays as long as two hours Monday night for New York City-area flights due to staffing issues.

"Due to the availability of staff tonight, the FAA must reduce the flow of aircraft in certain airspace serving New York City to maintain safety," the agency said. "Departure and arrival delays this evening could approach two hours at John F. Kennedy International, New York LaGuardia and Newark Liberty International airports. Passengers should prepare for delays."

The unusually specific announcement adds to this summer's travel woes, which have delayed and canceled thousands of flights amid higher-than-expected travel demand and shortages in key personnel areas, including pilots and air traffic controllers.

"It’s unusual to see the anticipated delays verbalized as due to lack of staff availability," Kathleen Bangs, a spokesperson for the tracking group FlightAware.com, said in an email.

She said Newark airport in New Jersey was already having 45-minute average delays and that La Guardia was experiencing 30-minute delays and increasing. A ground stop has also been issued for LaGuardia, meaning flights that have not yet taken off from the Queens, New York, hub will be delayed.