A heatwave gripped a large swath of the eastern United States this weekend. For many areas, the temperatures were extreme.

The threshold for what constitutes a heatwave varies by region, but here in the northeast, it is defined as three consecutive days with temperatures reaching 90°F or higher. In New York City, the official temperature in Central Park reached 91°F on Friday, and 95°F on both Saturday and Sunday. Overnight lows were also well above average. In fact, on Saturday, the temperature only cooled down to 82°F, tying the record warm low termperature for the date that was set in 2015.

When the humidity was factored in, it felt even hotter. The heat index ranged from 105°F-110°F.

The city’s airports, LGA and JFK, both in the borough of Queens, posted record high temperatures over the weekend, according to the National Weather Service. JFK hit 99°F on Saturday, breaking the previous record of 96°F that was set in 2013. On Sunday, LGA reached the century mark (100°F), tying the high-temperature record for the date at the site that was set in 1991.

The cause of this exceptional heat was two-fold. First, a large area of high pressure sitting over the central US was pumping hot air from the southwest toward the northeast. At the same time, a strong Bermuda High off the east coast was pumping warm, moist air from the Gulf of Mexico into the region. Together, they made it dangerously hot, which is why the NWS issued an excessive heat warning for the city. It is also why several outdoor events around the Big Apple were canceled, including the NYC Triathlon.

The hottest day ever recorded in New York City occurred on July 9, 1936, when the air temperature hit 106°F in the shade. The city’s normal high temperature this time of year is 84°F.