CHICAGO >> The swimming season kicked into high gear early in a large swath of the U.S., as a heat wave pushed temperatures into the 90s and beyond today in a stretch spanning from northern Florida to the Great Lakes and covering about a third of the country’s population.

The National Weather Service maintained an excessive heat warning through this evening for most of Illinois, Indiana and Ohio, which have been dealing with the sticky humidity and soaring temperatures since Tuesday.

The heat advisory in place for the Midwest and South stretched all the way eastward to the South Carolina shoreline.

Meteorologists warned that the high temperatures could be dangerous or deadly for some people and advised residents to stay hydrated, remain indoors if possible and take precautions if they must be outside.

Some of the affected areas were expected to get relief by Thursday. But the hot weather moving out could bring severe thunderstorms today to Iowa, Wisconsin and points eastward, including Michigan, according to the weather service’s Storm Prediction Center. Those storms could dump large hail or spawn tornadoes or damaging straight-line winds.

Utilities sorted out many of the power outages caused by storms that swept through the Midwest early in the week, but more than 200,000 customers remained without power still as of this morning, according to poweroutage.us.