The eastern US is the latest place to be hit with intense heat as the world plays a game of hot potato.

In the coming days, New York is expected to see temperatures rise to near 100 degrees Fahrenheit (38 degrees Celsius), but with humidity, it could feel more like 109 degrees Fahrenheit (43 degrees Celsius). Temperatures in other cities ranging from Detroit to Washington, DC, to Boston will see temperatures 20 degrees Fahrenheit above normal as the holiday weekend approaches.

The temperatures won’t be as high as they are in Phoenix. But this isn’t a dry heat; coupled with the humidity, anyone venturing outside is sure to experience roughly the equivalent of hanging out inside a dog’s mouth. Beyond the sheer grossness of hot, humid weather, there are also very serious health concerns.

Humidity hampers sweating—the most powerful tool the human body has to cool off. Sweat removes heat from the body by evaporating into the air, but this becomes less effective in humid conditions, when the atmosphere is already full of vaporized water. “When there’s high humidity, especially in a heat wave, it’s much more difficult for the body to physiologically cool off,” says Richard Allan, a climate scientist at the University of Reading.

The National Weather Service map of warnings is a patchwork of reds and pinks, with the agency raising extreme heat warnings and watches. While daytime highs will be eye-popping, overnight lows will be particularly problematic.

“Several days in a row of hot temperatures with little relief from overnight low temperatures can increase heat stress on the human body,” the NWS warned in its forecast.

That danger was underscored by New York mayor Zohran Mamdani, who wrote in a social post that New Yorkers should come up with a heat plan. First and foremost that means finding access to air conditioning, then checking on neighbors and people with illnesses that may make them susceptible to heat-related health issues.

The blast of extreme heat comes a week after Europe dealt with record-shattering temperatures. (The continent also saw blistering temperatures and high humidity in late May.) Burning fossil fuels has ensured that nearly every heat wave is more intense than it would’ve been in a preindustrial climate.

“The warming from rising greenhouse gases is clearly adding to global temperature, and that adds extra heat to the heat waves,” Allan says. “It promotes moderate heat to become extreme heat … These humid conditions may be more likely to be promoted into a hot, humid heat wave rather than just humid and warm.”

El Niño is another culprit that could be playing a role in this heat wave.

The natural climate phenomenon forms every few years in the tropical Pacific, but it affects weather around the world. That includes helping boost temperatures across the northern tier of the US and parts of Canada. El Niño was declared earlier this month, and it’s expected to be a particularly potent iteration that will only strengthen as summer goes on. With the hottest months still ahead, that means the odds are good that if you missed this chance to feel what it’s like inside a dog’s mouth, you’ll have plenty more chances.