The weather service says the warning about excessive heat will be in effect Monday from midday until early evening.
Forecasters say heat index values as high as 110 degrees are possible because of temperatures in the mid- to upper-90s and high humidity.
The advisory is in effect in Allendale, Berkeley, Colleton, Charleston, Dorchester, Florence, Georgetown, Hampton, Horry, Jasper, Marion and Williamsburg counties.
Forecasters warn the combination of heat and humidity could lead to heat illnesses unless proper precautions are taken. People who must be outside should drink plenty of fluids, wear light-weight clothes and stay out of direct sunlight if possible.
It’s best to do strenuous outdoor activities in the early morning or evening.