NEW YORK CITY >> A high-pressure weather system could bring record-breaking temperatures to central and eastern parts of the United States this week, National Weather Service forecasters said on Monday, threatening a large swath of the country with multi-day excessive heat.

Some 80 million people are currently under a heat advisory or warning as heat is expected to surpass 90 degrees Fahrenheit (32.2 degrees Celsius) and flirt with 100 degrees in some areas, which is 20 degrees above average this time of year, meteorologist Andrew Orrison of the National Weather Service said.

The heat wave comes as the nation prepares to observe Wednesday’s Juneteenth holiday, which commemorates the end of U.S. slavery in 1865. While it become an official federal holiday in 2021, Black Americans, especially in Texas, have traditionally celebrated the day with barbecues and other outdoor activities.

Officials are advising that people stay hydrated, limit strenuous activity in the sun and wear lightweight clothing.

The temperatures do not factor in humidity which will make it feel even hotter.

The heat index in parts of Indiana, Ohio and Michigan, as well as New England, could touch triple digits, the NWS said.

In New York City, a joint statement from the emergency management and health departments said cooling centers will open starting Tuesday and warned that high heat is a “silent killer.” Older adults and young children, as well as people with chronic conditions or who are pregnant, are the most at risk. Chicago has also announced that it will open cooling centers.

The NWS warned against leaving children and pets unattended in cars, given that sunlight can make the inside of a car heat up very quickly and cause vehicular heatstroke.

Temperatures are expected to remain elevated until the weekend.