New York City is sweltering through its second heat wave of the summer.

The threshold for what constitutes a heat wave varies by region, but here in the NYC area it is defined as three consecutive days with temperatures reaching 90°F or higher. Monday marked the city’s fifth.

With dew points – a measure of humidity – in the mid to upper 70s, it felt even hotter. The heat index – the so-called real feel temperature – reached as high as 105°F to 110°F in some spots.

This dramatic rise in heat and humidity was the result of a dominant Bermuda High, a large area of high pressure situated off the east coast. Spinning clockwise, it has been steering hot, humid air from the Gulf of Mexico toward the northeast.

While these conditions are oppressive, they can also be dangerous. The NWS issued both an excessive heat warning and air quality alert for the city. The last time NYC had this type of heat emergency was July 2013.

How a Bermuda High ushers in hot and humid air to the northeastern US. Credit: Jacksonsweather.com