 And when you factor in more humidity, which will be in play tomorrow, that 100 degrees will feel closer to 110 to about 112 degrees. That's why the National Weather Service will issue an excessive heat warning beginning at 11 a.m. lasting until about 8 p.m., which is when we expect those hottest temperatures. Now remember your heat safety. That includes taking plenty of breaks in the shade if you have to be outside.