As a heat wave hits multiple U.S. states, some areas are have been placed under extreme heat watches and warnings.

Philadelphia is under an extreme heat warning with heat index values up to 105 degrees, advising residents to stay cool and hydrated.

An "extreme" heat warning has been issued for 16 U.S. states on Tuesday morning. The National Weather Service is warning 16 U.S. states of extreme heat on Tuesday, June 24. Temperatures in many U.S. states are expected to reach the high 90s and possibly low 2000s.