If you’re out of sunblock, it’s time to stock up. As Fourth of July week rolls in, an estimated 162 million are bracing for a record-breaking heatwave. Extreme heat watches, warnings, and advisories are in effect for portions of 35 states, including Florida, Georgia, and South Carolina.

As the week continues, temperatures are expected to skyrocket into the upper 90s and 100s. It may feel even hotter as heat index values reach up to 115 degrees. On Monday, the hottest temperatures will target the central and Southeastern U.S., with heat index values increasing up to 110.

There's no relief in sight as the heat dome expands Northeast on Wednesday. At-risk cities include, but aren’t limited to, Philadelphia, New York City, Chicago, Baltimore, Washington, D.C., and Boston. On Friday, New York is expected to see record-high temperatures, potentially reaching 95 with a heat index of 106.

Chicago Mayor Brandon Johnson issued a statement on Monday, warning Chicagoans to prepare. “If you can, stay inside with air conditioning on. If you do not have air conditioning, keep your blinds closed, but windows slightly open”. Around the city, six cooling centers will be open to the public. Johnson urges residents to drink water and check in on vulnerable community members.

According to Mike Bardou, Warning Coordination Meteorologist at the National Weather Service, ailments caused by heat take victims by surprise. “Heat is kind of one of those sneaky things, in a sense, relative to a thunderstorm coming or blizzard, you don’t necessarily realize the effects until it’s too late,” Bardou said. “And the effects of heat are cumulative, so day by day that goes by that you don’t have that ability to recover, cool off, the effects are worsening.”

This heatwave comes as no surprise to the West, which has been fighting wildfires since the weekend. Around two million people are currently under fire warnings in four states, including New Mexico, Arizona, Colorado, and Utah. The largest Utah fire now covers more than 93,000 square miles and is 0% contained. This holiday heatwave exponentially increases the risk of wildfires, with portions of the Southwest reaching critical levels by Tuesday.