Over 700 US flights canceled, with more expected, due to weather

The Federal Aviation Administration is warning that it'll likely start rerouting and holding flights throughout the Northeast as well as in Atlanta, Denver and Florida airports due to weather.

Airlines have already canceled more than 730 U.S. flights on Thursday.

New York City's airports -- John F. Kennedy International Airport, LaGuardia Airport and Newark Liberty International Airport -- are currently seeing the biggest impacts. At JFK, the average flight delay is over three hours.

This comes as severe thunderstorm watches were issued for Thursday afternoon and evening from New England to upstate New York and down through New York City, Philadelphia and Washington, D.C.

Strong, slow-moving thunderstorms could bring torrential rain and trigger flash flooding. A flood watch is in effect across much of New England, including Hartford, Connecticut, and Boston.

The Northeast threat should end by Thursday night.

But the Northeast is also facing what'll likely be the region's first heat wave of the summer.

From Thursday to Saturday, the heat index -- what the temperature feels like with humidity -- is expected to reach over 100 degrees in New York City, Philadelphia and Washington, D.C.