Extremely high temperatures have stricken the Midwest and are certain to persist throughout the week. The extreme discomfort will soon spread to the East Coast. Eighteen states issued heat watches, warnings or advisories. Some states have experienced record high temperatures.

The National Weather Service put 18 states stretching from North Dakota to Texas and East to Ohio under a heat warning, watch or advisory. It said as many as 13 deaths in the past week in the Midwest could be blamed on the effects of the heat. When humidity was factored in, the heat index made it feel as hot as 110 degrees in a broad swath of the nation. “This is unusual,” said Pat Slattery, spokesman for the Weather Service.

The heat index easily surpassed 100 degrees in many places, including 126 in Newton, Iowa, and 119 in Madison, Minn. But few people are hit as hard as the poor. In Oklahoma, for example, applications from elderly and low-income residents are pouring in for help to pay utility bills. And Chicago officials have opened six cooling centers, many of them in lower-income neighborhoods, along with hundreds of air-conditioned public buildings

“This heat is dangerous on many levels,” said Jack Hayes, director of the National Weather Service. “Temperatures and humidity levels are high, the heat will be prolonged, and very warm temperatures overnight won’t provide any respite. All of these factors make this an unhealthy situation, especially those in the upper Midwest who are not accustom to such heat.”