The hot air moved in from the West, where 21 people, mostly homeless, have died from heat this summer in Arizona's Phoenix metro area. Some 200 cities and towns in the West hit daily record highs last week, including Las Vegas, Nev., at 117, and Death Valley soared to 129, the weather service said.
Demand for electricity to run air conditioners has hit near-record peaks from Southern California to the region served by the Tennessee Valley Authority.
Excessive heat warnings and advisories were in effect through Monday for states from Illinois to Louisiana and from Nebraska to the District of Columbia, the weather service said. In the Florida Panhandle, meteorologists said a high of 94 combined with high humidity could make the heat index 114 Monday afternoon.