Blistering heatwave scorching much of the U.S.

Over 170 million people were left sweltering by a nationwide heat wave, sparking fears of power outages, transit delays, and health hazards.
3:36 | 07/20/19

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Transcript for Blistering heatwave scorching much of the U.S.
I'm Tom llamas. We begin with the blistering heat scorching much of America tonight. From New Mexico to Maine, 170 million people sweltering in excessive heat. The hottest weekend of the summer. For many, the hottest in years, and some serious power outages as well. At dawn this morning, Washington, D.C. Already felt like it was 87. Subway riders in New York sweltering underground. One of the biggest fears? Power outages. Thousands in the dark in Baltimore. Little relief overnight from these brutal temperatures. Searing heat index numbers expected again tomorrow. The heat emergency is a health emergency. A former NFL lineman succumbing to heatstroke in Arkansas. The national weather service warning, take the heat seriously. ABC's Kaylie Hartung starts us off right here in New York. Reporter: Severe storms fueled by the heat tonight creating a new emergency. Hundreds of thousands in Michigan are without power while temperatures outside feel like they're in triple digits. I don't know if it gets any hotter than this, but it's not the heat -- it's the humidity that's the problem. Reporter: In New York City, still investigating the cause of a blackout last weekend, the mayor questioning how much stress the power grid can handle during this heat wave. The problem is we still don't have a clean answer about what happened last Saturday, which is not inspiring confidence, so we are keeping a very close eye on coned. Reporter: Along the I-95 corridor, millions melting in the humidity. In Boston where there is a heat emergency, some finding relief in water parks. The same in North Carolina. More than 170 million across the country enduring potentially life-threatening conditions. This infrared camera showing just how hot it feels. It's, like, sucking the life What are you doing to stay cool? Eat ice cream. What kind of precautions are you guys taking? Definitely keeping them hydrated. Having them drink lots of water. Reporter: Officials across the country trying to avoid scenes like this one in Atlanta. Reminding parents not to leave their children inside cars. And the humane society in Toledo on patrol looking for dogs like this one that were left out in the heat. Good reminders on a night like this. Kaylie Hartung joins us live outside a fountain in New York in the village where people are trying to beat the heat. Officials warning people to limit outdoor exposure? Reporter: That's right, Tom. Officials delivering strong advice for people to stay out of the sun and stay hydrated. They also want people to remain vigilant, encouraing you to check on your neighbors and if you see anyone in distress, call 911 immediately. This isn't over when the sun goes down tonight. Tomorrow, millions will be experiencing the brutal temperatures still. Tom? Some very important tips tonight. We should mention, this is Kaylie's first report on "World news", so Kaylie, welcome to you. We turn to meteorologist Jeff Smith from WABC. He's tracking it all. Dangerous conditions out there for so many this weekend. Is there any relief in sight? I can attest, pretty brutal out here right now in New York City. The good news is there is relief in parts of the country tomorrow. In places like Chicago where the heat index is 105 degrees, tomorrow is only going to be in the upper 70s. Still dangerous heat from the southern plains up through the I-95 corridor. Heat index in the nation's capital up to 110 tomorrow. 107 in New York City. But even along that corridor, we improve middle of next week with big relief coming Tuesday to Wednesday. Along that barrier, some severe thunderstorms affecting the great Lakes today. That could move into the northeast by Monday. Jeff Smith, thanks to you.

This transcript has been automatically generated and may not be 100% accurate.

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