This scorching season's hottest temperatures are currently sweeping across the eastern United States, with cities in the Northeast facing the brunt of the heatwave on Wednesday after the Midwest endured extreme temperatures earlier this week.

Chicago reached a sweltering 99 degrees Fahrenheit on Tuesday, shattering the city's daily record of 97 degrees. The heat index, which reflects how hot it feels due to humidity, climbed to a blistering 115 degrees in Chicago on Tuesday.

On Wednesday, a heat advisory is in effect for 55 million people spanning from Missouri to New York City.

The heat index is projected to reach 105 degrees in Philadelphia and Washington, D.C.; 102 degrees in Cincinnati, Ohio, and Louisville, Kentucky; 104 in Richmond, Virginia; 103 in Nashville, Tennessee; and 96 degrees in New York City and Pittsburgh.

The intense heatwave will subside in the Northeast by Thursday, but will persist in the Ohio Valley and Tennessee Valley until Friday.

Record high temperatures are possible in Nashville, Cincinnati, and Raleigh, North Carolina, by the end of the week.

The Centers for Disease Control and Prevention (CDC) estimates that hundreds of Americans die each year due to extreme heat, but experts believe the true number may be significantly higher.

Last year witnessed a record-breaking number of heat-related fatalities in the United States, according to the prestigious medical journal JAMA.

Click here for tips on how to stay safe in the heat.