A sweltering heatwave is set to firmly grip the Piedmont region of Northeast Georgia, North Carolina and upstate South Carolina, with astronomical heat index values that could soar up to 108, according to the National Weather Service (NWS). Residents in Charlotte and surrounding areas are under a heat advisory effective from 11 AM until 8 PM EDT today, as the mercury is expected to climb near the century mark, combining with high humidity to produce potentially dangerous conditions. The NWS cautions that hot temperatures and high humidity may cause heat illnesses.