Evansville's heat index hottest in the country - 109 degrees at 2 p.m., Thursday

The heat index reached 109 degrees, according to figures from the Weather Channel.

It was so hot, two Evansville Habitat from Humanity workers were excused for the day, showing signs of heat exhaustion.

Parts of Florida, the southernmost state in the continental U.S., had heat indices sitting at a cool 87 degrees. And Southern Arizona was at 97 degrees at 11:30 a.m.

Heat index is a measurement of how hot it feels outside when humidity is taken into consideration with the actual temperature.

The National Weather Service in Paducah, Kentucky, said the extreme heat and humidity will continue until tomorrow, then Friday, we'll see highs in the mid-80s.

Saturday will feel even better as humidity is expected to taper off. Highs will remain in the mid-80s.

Louisville Courier-Journal reporter Lucas Aulbach contributed to this report.