An oppressive heat wave that has gripped the central and southern United States for days is moving east, bringing temperatures as high as 38 degrees Celsius to an area stretching from Chicago to Washington.

The National Weather Service said Thursday that excessive heat watches, warnings and advisories are in effect for much of the central and eastern United States.

Media reports say some two dozen people have died recently from heat-related causes.

Record-breaking temperatures were expected in the eastern U.S. Friday and Saturday, and forecasters say the heat is likely to linger into August.

Experts say the unusually hot weather is caused by a condition called a “heat dome,” in which a high pressure system pushes down on a layer of hot, humid air.

Authorities are warning people to drink lots of water and stay inside when possible. Some locations have cooling areas for people to escape the heat.

Meanwhile, some zoos have set up electric fans and are giving animals ice to help them stay cool.