A relentless heatwave gripped the country from the central states to the East Coast Saturday, prompting cancellation of the New York City Triathlon and producing cracked and buckled roads in some Plains states. Some East Coast cities braced for temperatures in the triple digits.

As the stifling heat — expected to affect 200 million people — settled in for at least a fifth day, the National Weather Service issued an Excessive Heat Warnings and Heat Advisory from parts of the Texas Panhandle to the Ohio Valley, around the Great Lakes, parts of the Mid-Atlantic and in the Northeast.

An Excessive Heat Warning is issued when the combination of heat and humidity is expected to make it feel like it is 105 degrees or greater.

Daytime temperatures in the mid to upper 90s or higher plus high humidity will result in heat indices as high as 115 for some, forecasters said.

Washington, D.C., Philadelphia, New York and Boston were bracing for weekend temperatures in the triple digits. New York City and Baltimore were under a Code Red Extreme Heat Alert that is expected to continue through Sunday.

"It’s been since July of 2012 that Chicago and Philadelphia both hit 100 degrees, and Washington, D.C., hasn’t hit 100 since August of 2016," says AccuWeather Meteorologist Danielle Knittle.

In addition, forecasters warned that overnight temperatures were not likely to fall far enough to bring relief, particularly in larger cities, like Chicago, St. Louis and New York City.

Cities in Vermont and New Hampshire opened shelters where people could cool off.

The heat comes as hundreds of thousands of people in Michigan and Wisconsin lost power following weekend storms. In parts of Wisconsin, the storms caused so much damage that power companies will have to rebuild parts of their networks, and people could be without power for days.

In New York City, officials canceled Sunday's New York City Triathlon. Likewise, Mayor Bill De Blasio scrapped the two-day outdoor OZY Fest in Central Park featuring soccer star Megan Rapinoe, musician John Legend and “Daily Show” host Trevor Noah.

De Blasio also directed owners of office buildings over 100 feet tall to set thermostats to 78 degrees Fahrenheit through Sunday to conserve energy.

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In Sioux Falls, South Dakota, traffic was back up along I-229 after a large section of road buckled under the heat. Traffic on the Interstate 229 southbound lanes was backed up Friday afternoon because a large portion of road buckled under the heat.

In south-central Kansas, around Wichita, two roads also cracked this week as temperatures reached 100 degrees and higher.

“The buckling is essentially caused by concrete, which is more rigid than asphalt, expanding to the point it breaks open at a weak point during hot weather,” said Tim Potter, a Kansas Department of Transportation spokesman, The Wichita Eagle reported. “Sometimes, the pressure can cause concrete to explode into the air. The problem also can occur when asphalt is laid over concrete. The dark asphalt absorbs heat and can add to the pressure.”

Wisconsin Gov. Tony Evers declared a state of emergency after two fires broke out at electric substations in Madison, WISC reported. He said he issued the declaration to "provide support during the large power outage that is exacerbated by the extreme heat wave affecting the area."

The Weather Channel offers a bit of good news after the weekend: A dip in the jet stream will spread from the upper Midwest on Sunday to the East Coast by Monday, ushering in cooler, drier air to much of the Plains, Midwest and East.

Contributing: Olivia Sanchez; Sophie Carson, Milwaukee Journal Sentinel; Natalie Brophy, Wausau (Wis.) Daily Herald; The Associated Press