Philly has already seen more 90+ degree days than some entire years

It’s way too early to say how hot this summer will end up, but so far it’s been a barn burner.

By the time the current heat wave stalls for a brief respite on Friday, we’ll already have seen more 90 degree or above days this year through July 11 than we experienced during all of a dozen of the last 50 years.

Indeed, another heat wave — defined as three consecutive days of temperatures in the 90s — is on its way after the remnants of Hurricane Beryl are expected to cool things down briefly.

The National Weather Service is calling for temperatures to soar back into the 90s possibly by Saturday. The heat will last at least through a sticky-icky Wednesday, with some days reaching the high 90s and heat indexes likely over 100.

The Inquirer analyzed 50 years of daily weather data for Philadelphia International Airport stretching from 1974 through this week. By Thursday, the last day of a predicted seven-day heat wave, Philadelphia will have already seen 19 days of temperatures hitting at least 90 degrees.

That would place 2024 among the top four years for such a heat spell through July 11.

Put another way, as of Thursday, we’ll have seen as many 90 or higher degree days as 14 other full years.

An early heat wave helped make the month of June the fourth warmest stretching all the way back to 1872. Of the 15 warmest Junes in Philly over that extended period, nine have occurred since 2001.

» READ MORE: What one of Philly’s warmest Junes on record may mean for the rest of summer

The data show that 90 degree days are common even in September. Some 90 degree days have come as early as April and stretched into October.

But July acts like a heat-seeking missile.

Shel Winkle, a Texas-based meteorologist with Climate Central, a nonprofit that includes scientists who analyze climate trends, said the meteorological summer of June, July, and August began with a swelter.

“For the Northeast, the heat started early so you didn’t get a chance to acclimate,” Winkle said. “It was a run-up to late summertime heat right all at once and it was extended.”

Winkle noted the difference between weather, which includes short-term patterns, and climate change, which is marked by long-term patterns. Summers are supposed to be hot. But over time, he said, they are proving hotter for longer periods than in past decades.

“What we know in a warming climate is that these heat domes and these heat waves become more intense, so temperatures are hotter,” Winkle said. “They become longer in duration, like what you’re dealing with this summer.”

Winkle said that 50 years ago, a typical Philly summer saw about 20 days above 90 degrees for June, July and August, representing about 22% of the days. Now, about 32 days over the summer are 90 degrees or more days, representing about 35%.

That’s especially unwelcomed news for people who live in parts of the city where temperatures can be 10, 15, or even 20 degrees hotter than others because of the urban heat island effect.

» READ MORE: These Philly neighborhoods get the worst of the summer heat

According to an analysis by Climate Central, more than half a million people in Philadelphia live in neighborhoods affected by an urban heat island effect of more than 9 degrees compared to those living in nonurban areas — only behind New York and Chicago.

The heat island effect is caused by buildings, roads, and other infrastructure that absorb and re-emit the sun’s heat. Dark surfaces, such as black asphalt roofs, reflect less light and retain more heat. As a result, certain areas can become hotter during extreme heat compared with suburban and rural areas, according to the U.S. Environmental Protection Agency.

Winkle said we could see cooler temperatures later in the summer that brings averages down, or a cooler summer next year. But the trend is clear, he said.

“The Northeast is one of the fastest warming sections of the country,” he noted.