Sweltering and "dangerous" heat with indices surpassing 100 degrees Fahrenheit across parts of nine states has prompted the National Weather Service (NWS) to issue warnings for millions of Americans. Newsweek has reached out to NWS for comment via email on Thursday.

See which states feel hottest The map below identifies areas where the heat index is forecasted to reach NWS-defined levels from "Caution" (80 degrees Fahrenheit) to "Extreme Danger" (above 125 degrees).

A heat advisory goes into effect Thursday for parts of Connecticut where heat index values will soar past 100 degrees on Friday.

Chicagoans are stepping up to help one another during another heat wave in the city. The temperature reached 94 degrees Wednesday, with a heat index of 105, according to the National Weather Service. An extreme heat warning is in effect through much of Thursday, when temperatures are forecast at a high of 94 and a heat index of 103.

Scorching temperatures combined with the high humidity are expected Thursday, July 24, the National Weather Service stated in the advisory. The advisory will be in effect from 11 a.m. through 8 p.m., with the head index reaching a high of 105.

The cooler, more comfortable first half of the week will soon be behind us as New England ushers in a peak summer scenario of hot, sweltering weather and increasing humidity through Friday that will see heat index values soar.

The National Weather Service (NWS) in Mount Holly is warning residents across New Jersey to prepare for a rough combination of extreme heat and strong thunderstorms. An Extreme Heat Warning will be in effect for the busy I-95 corridor from 10 a.