Kansas City, Mo. ? Heat indexes were back in the triple digits Monday in northeast Kansas and Missouri, where six deaths last week may have been linked to the heat.

The National Weather Service issued heat warnings Monday for much of the area with temperatures expected to be in the upper 90s to about 100 through Friday. Nighttime lows, which would likely hover around 80 degrees, were unlikely to provide much relief.

Heat indexes, which measure how hot it feels, were expected to fall in the 105- to 115-degree range because of high humidity in the region, said Noelle Runyan, meteorologist for the National Weather Service.

The latest heat wave follows one early last week in which six suspected heat-related deaths were reported in Kansas City. Those deaths were still under investigation Monday, according to the Kansas City Health Department.

Last week, temperatures rose well into the 90s. The heat abated some late last week, only to rise into the 90s again Sunday.

“It is August. It’s summertime in the Midwest, and we do expect heat. But this is extreme,” Runyan said. “This is going to be persistent, extreme heat.”

Extreme heat warnings also have been issued for southeast Nebraska and southwest Iowa, and heat advisories were issued for spots all the way down to the Gulf Coast, she said.

Thunderstorms forecast for tonight in some areas could reduce temperatures slightly.

One or two days of excessive heat is more common and easier to manage than a heat wave that lasts several days, Runyan said.

The lingering heat can be a problem for many people, particularly the elderly, the overweight, young people and the mentally ill, said Jason Eberhart-Phillips, director of health at the Kansas Department of Health and Environment.

“Certainly when you have day after day of extreme heat, and the nighttime temperature doesn’t cool things down adequately, people who are most vulnerable to heat-related illnesses become a concern,” he said.

Carol Braun, an epidemiologist with the Missouri Department of Health and Senior Services, said 30 heat-related illnesses were reported last week in Missouri.

But she also said this summer’s heat wave has not been as bad as one in 1980 that claimed 285 lives.

“The best response to the hot weather is to try to be in air conditioning, especially during the hottest parts of the day,” she said.

Across the region, officials have been taking precautions to deal with the high temperatures. St. Louis Mayor Francis Slay’s office planned automated telephone calls with tips for residents on dealing with hot weather and reminding them to check on friends, neighbors and relatives who might struggle in the heat.

The Kansas City Chiefs pushed afternoon practice for training camp in St. Joseph back to 6 p.m. “for the safety of Chiefs players and fans.”

And Johnson County, Kan., opened all its libraries as cooling centers. In the St. Louis area, 75 cooling centers were opened with air conditioning and cold water.