Triple-digit temperatures are about to crank up another notch.

Temperatures are expected to climb to 115 degrees Tuesday through Thursday as an extreme heat warning takes hold over Pinal County.

The National Weather Service in Phoenix issued the warning as a large area of high pressure settles over Arizona, driving highs into the danger zone through midweek.

“A watch means that the ingredients are available that may produce extreme heat,” said Mark O’Malley, an NWS meteorologist in Phoenix. “Warning means everything is coming together and that extreme heat is right over the horizon.”

O’Malley advised residents to schedule outdoor activities for early morning or evening and to take breaks indoors during peak afternoon heat.

City officials say the Maricopa Library and Cultural Center is a designated cooling center, though it’s intended as a last resort. Residents should have a backup plan in place in case their air conditioning fails, said city spokesperson Monica Williams. Pinal County lists additional cooling and hydration sites at pcceh.com.

Maricopa’s Emergency Manager Angela Eastman said extreme heat causes more weather-related deaths annually than any other disaster. She urged residents to stay hydrated, keep homes cool with closed curtains and cool showers, and check on older neighbors, children and pets.

Anyone showing signs of heat exhaustion or heat stroke should call 911 immediately.