An extremely dangerous heat wave is underway for the eastern half of the United States as a potent heat dome reaches its peak, bringing the hottest temperatures of the year so far – the hottest in years for some cities – and putting tens of millions at risk.

Coming originally from the Pacific, a dome of high pressure is parking over the Eastern United States with hot air from the Southwest that already made an uncomfortable rest stop in the Midwest.

Extreme humidity and triple-digit temperatures are affecting around 250 million people across the United States. Here's the science behind the heat dome that’s stifling the nation.

A massive heat wave is unleashing the hottest weather in years across the eastern United States, and the temperature in New York City could hit triple digits for the first time in over a decade.

Dangerous heat will affect the tri-state area through Wednesday before a cold front brings relief to the region.