The National Weather Service is warning an “extremely dangerous heat wave” is expected to continue over the Southwest this week and is expected to start spreading eastward Monday. 

“Beginning Monday, dangerous heat will build in the Gulf Coast and Southeast U.S. again, with widespread heat index readings over 110 degrees through Friday, before refocusing in the Southwest and western U.S. next weekend and beyond,” the warning read. 

The weather service warned heat levels could break records in the Southwest, including in the San Joaquin Valley, Mojave Desert and the Great Basin regions.

Phoenix, in particular, is expected to reach its hottest seven-day average temperature on record. For the past two weeks, Phoenix reportedly has experienced temperatures above 110 degrees each day.

The National Weather Service warned heat is the “leading weather-related killer” in the United States.

“Take the heat seriously and avoid time outdoors. Temperatures will reach levels that would pose a health risk, and be potentially deadly, to anyone without effective cooling and/or adequate hydration,” the alert said. “Overnight temperatures will provide very little relief.”