Hello from CNN, I'm Joe Beck. With the five things you need to know for Tuesday, June 18th.

One of the worst heat waves in decades is sending temperatures soaring for more than half of the US population.

Hundreds of temperature records could be matched or broken and around 270 million

Americans are forecast to see heat at or above 90 degrees this week.

The National Weather Service says the Great Lakes to the northeast will get the worst of it.

An extreme heat risk is in place there and while tomorrow and Thursday will be the hottest days of the week, the surrounding days will only be slightly less brutal.

Temperatures are expected to reach dangerous levels in several cities, including New York, Boston, and Chicago.

New York City officials, Zach Iskull, says the heat there could reach close to 100 degrees

later this week.

These numbers are dangerously high.

The cumulative effect of prolonged heat can be especially dangerous

as the body's ability to regulate temperature becomes increasingly strained.

And a tropical storm watches in effect for parts of southern Texas to northeastern Mexico, kicking

off what's expected to be a hyperactive hurricane season. Meanwhile, large and fast moving wildfires have forced evacuations in California and New Mexico.

In LA County, the post fire has burned more than 15,000 acres and is now 20% contained.

CNN's Camilla Bernel says firefighters have told her the recent conditions are helping fuel the flames.

And climate change also greatly impacting the way these fires are spreading.

You know, firefighters telling me that because of the rain that we got here in California over the last couple of days

you have a lot of vegetation and in particular you have a lot of grass and that is

what firefighters call fuel so you add in the wind the low humidity is what

firefighters call fuel. So you add in the wind, the low humidity, the high temperatures,

and that's what makes this fire just so dangerous.

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