© Tom Pennington/Getty ImagesStorm clouds build offshore in Clearwater, Florida. Tampa area residents wait for tropical storm Isaac.
The airports in Miami and Fort Lauderdale were hit the hardest, cancelling 589 flights - the vast majority of the 742 U.S. flights grounded overall because of the storm as of Sunday afternoon, according to the flight-tracking service FlightAware.
American Airlines and its American Eagle affiliate cancelled 486 flights. The last American flight left Miami at noon Sunday. The airline expects to be fully operational out of Miami by noon Eastern time on Monday, said airline spokesman Matt Miller. American runs a hub in Miami, a jumping-off point for flights to the Caribbean and Latin America.
Overall, airlines have cancelled 184 flights for Monday but expect to be operating normally by late Monday, according to FlightAware.
Isaac, already carrying winds of more than 60 miles an hour, was expected to cross the Keys by late afternoon. The storm will likely pick up strength from the warm, open waters of the Gulf of Mexico and strike as a dangerous Category 2 hurricane somewhere between New Orleans and the Florida Panhandle on Wednesday, the seventh anniversary of Hurricane Katrina.
Louisiana Governor Bobby Jindal declared a state of emergency ahead of Isaac late Sunday and urged voluntary evacuations for coastal parishes in the state.
