Forecasters say the heat wave gripping the central U.S. is "unrelenting" and sweaty residents shouldn't expect any relief soon.

Heat advisories and warnings are in place in 17 states, from Texas to Michigan, as temperatures and humidity combine to make being outside uncomfortable for millions.

In Oklahoma City, forecasters expected another day of 100-degree heat Sunday, which would be the 27th day this year the city has reached 100 or above. The city's record is 50 such days, set in 1980, and it's on pace to break it this year.

National Weather Service forecaster Daryl Williams in Norman, Okla., says much of the central U.S. is under a so-called "heat dome" that isn't moving much. He describes the heat as "unrelenting" and says the trend is for more hot weather.