Hot and humid air is poised to smother parts of Minnesota this week in what could be the worst heat wave of the summer.

The high temperatures forecast across the southern half of the state and the Twin Cities are part of a heat wave projected to stretch across most of the center of the United States, from the Twin Cities down to Texas, according to the National Weather Service. The actual temperatures in Minnesota are projected to reach the mid-to-upper 90s until Thursday, with humidity making it feel several degrees warmer.

"We'll have really moist air coming in, so it's going to feel really uncomfortable," said meteorologist Caleb Grunzke in the weather service's Chanhassen office.

The heat will start building in southwestern Minnesota on Monday, he said, with an excessive heat warning for much of southwestern and southern Minnesota stretching from Marshall and Worthington to Albert Lea and Mankato. It will feel like the low 100s, Grunzke said.

On Tuesday, the heat is expected to slide up the state, blanketing the Twin Cities and western Wisconsin. Temperatures are forecast in the low-to-mid 90s, with the heat index — the "feels-like" measure that accounts for humidity — somewhere between the high 90s and low 100s.

Wednesday is projected to be the hottest day of the week, with the temperature possibly reaching 100 degrees in the Twin Cities, and humidity making it feel even warmer.

Grunzke said anyone who is working outside should try to take frequent breaks, stay in the shade as much as possible and drink plenty of water. Afternoon sports practices could become dangerous, he said.

Nights won't offer much relief. Lows will only dip down to the mid-70s for the Twin Cities. That long-lasting heat can be especially dangerous for sensitive groups.

Hennepin and Ramsey counties are reminding residents that air conditioned rec centers and libraries can provide respite from the heat, as well as other spots like movie theaters and shopping centers.

It's unusual to have a string of such hot days in August, Grunzke said, because there are fewer daylight hours than in late June and early July. So far in 2023, the hottest day in the Twin Cities was July 27, when the temperature hit 96.

The Twin Cities have not recorded a 100-degree day in August since 1988, according to the National Weather Service.

The heat should start to dissipate Thursday — just in time for the opening of the Minnesota State Fair.

Overall, Grunzke said, the summer of 2023 has been warmer than average. In July and so far in August, the temperature has been 1.5 degrees warmer than average, and June was 5 degrees warmer than average.