‘Heat warning’ is declared in Philly, and the danger is about to peak, health experts warn

As what is becoming one of Philly’s longer heat waves in recent years reaches its crest, it may be taking a dangerous and possibly deadly turn this weekend, health officials are warning.

As heat indices rocketed into the triple digits on a blistering Saturday — this, after the city may have tied a 114-year-old daily record for the highest overnight minimum temperature — the National Weather Service declared an “excess heat warning” that will remain in effect until Sunday evening

The intensity of Sunday’s heat and sultriness are forecast to qualify as “extreme” and “rare,” ranking at the highest level on the National Weather Service’s experimental “HeatRisk” hazard scale.

The city has a heat health emergency in effect.

At 3 p.m. Saturday the temperature reached 97 at Philadelphia International Airport — the highest of the year — and the heat index was 104. The unofficial low Saturday was 75, which would tie the 1910 record for the highest minimum temperature for a June 22.

Temperatures overnight may not get below 80 in parts of the city, said Ray Martin, a lead meteorologist with the National Weather Service Office in Mounty Holly, and then Sunday is expected to be a clone of Saturday.

But showers, which were isolated Saturday — “One just happened to be over the city,” said Martin — may be more plentiful.

Of perhaps more concern would be that after several days of cumulative heat, the city may well set more records for the lack of overnight cooling Sunday and Monday, as temperatures fail to get below 75 degrees.

“The thing about heat waves that can cause someone to die is the overnight temperature,” said city Health Department spokesperson Jim Garrow.

Hot nights are especially dangerous for the elderly who live alone without air-conditioning. That was evident during the deadly Philadelphia and Chicago heat waves in the 1990s and the horrific heat that was blamed for killing tens of thousands in Europe in 2003.

“If homes, especially the rowhouses, don’t cool at night,” said Garrow, “the interior temperature starts off the next day at a higher starting point, meaning it can get hotter sooner and for longer. Multiply that effect over a series of four or five days, and our homes and bodies don’t get the chance to just cool off.”

“That’s why we encourage people to seek out air-conditioning, even if just for a few hours per day, to lower their body temperature.”

Sunday in Philly is expected to rank as “extreme,” the highest level on the three-tier “heat ranking system” developed by Climate Analytics Inc., said company president Laurence Kalkstein, a climatologist and heat-mortality specialist.

But given the overnight warmth, he also is calling for “extreme” conditions again Monday, even though highs are expected to back down to the lower 90s.

In his system, Sunday and Monday have the highest probabilities of heat-wave mortality during this hot spell, which is due to continue into midweek.

While Philadelphia doesn’t use rankings, Kalkstein is well familiar with Philly summers: He helped the city and the weather service develop a highly praised heat-response system, aspects of which are still in play today.

That includes the Philadelphia Corporation for Aging “heatline” — 215-765-9040 — which will be in operation from 8:30a.m. until 11:59 p.m. through Sunday, along with commonsense advice, such as checking in on elderly neighbors.

NOAA and the Centers for Disease Control and Prevention credited Philadelphia’s system with saving lives. Four times as many people died from heat-related causes in 1993 as in all of the last 10 years, according to Health Department statistics.

The cold front due to push through on Monday is expected to provide a measure of relief later in the day into Tuesday by drying out the air.

Still, highs are forecast to rise above 90 degrees on Tuesday and well into the 90s on Wednesday, which would make this a nine-day heat wave. Philly had 10-day stretches in 2022 and 2012. The city hasn’t had a streak of 90-plus highs for more than 10 days since the 1990s. Its longest was 18 days, in 1988.

And if the forecast holds (and when has that ever failed to happen) this streak will end Thursday, when highs are expected to go no higher than the upper 80s.

By then, that might seem cool.