Record temperatures seen as heat wave plagues 23 states

(CNN) -- A heat wave is building and could reach dangerous levels in parts of the Midwest, the Plains and the Southeast this week.

Twenty-three states were under heat advisories Monday, according to the National Weather Service.

Kansas City, Missouri, and St. Louis are under an excessive heat warning, along with Tulsa, Oklahoma; Memphis, Tennessee; and Evansville, Indiana. In these areas, the heat index, or how hot the body feels due to the combined effects of heat and humidity, will reach between 110 and 115 degrees this week.