Heat warning is in effect for Philly for ‘dangerously hot’ conditions into Sunday evening

It was at 2:47 p.m. Saturday that the National Weather Service declared that a “watch” now was an “excessive heat warning” for the Philadelphia region, and by then that was a declaration of the obvious.

The heat index had soared into triple figures, and although no measures of temperature and atmospheric moisture can capture precisely how we feel, Saturday was beyond argument the most sultry afternoon of the year. The temperature reached 98, the highest reading since August 2022. The morning low, 75, tied the 114-year-old record for the highest minimum temperature for a June 23.

After what is likely to be another record-warm morning, forecasters say Sunday is shaping up to be Saturday’s evil twin with highs again well into the 90s, with 100-plus heat indexes.

But it may come with one important difference, said Ray Martin, a lead meteorologist at the National Weather Service office in Mount Holly: Widespread showers are expected in the afternoon and evening.

While that sizzling sound you heard Saturday may have been one of those random raindrops landing on a hot sidewalk near you, the storms missed just about every square block of the region.

Real relief is forecast to build in Monday afternoon with the passage of a front, but not until another overnight warming record is likely Monday morning, and health experts say that is more concerning than the attention-getting triple-digit numbers.

Sunday would mark the sixth consecutive day of 90-plus temperatures, and Monday, the sixth straight morning on which the temperature failed to drop below 71.

Cumulative heat inside homes without air-conditioning can be life-threatening for the elderly and physically vulnerable, health officials warn. Not only does it make sleeping difficult, the lack of cooling allows the inside temperatures to rise rapidly when the sun comes up.

All that takes a dangerous physical toll. “Biologically, you don’t have that reprieve,” said Martin.

Official lows early Sunday and Monday may go no deeper than the upper 70s, but Martin pointed out that would be at Philadelphia International Airport.

In the city, where tree canopies are wanting and buildings and paved surfaces have been sunning themselves and storing heat, chance are that the temperatures won’t drop below 80.

“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,” said Health Department spokesman Jim Garrow.

That advice may be especially important Sunday, when the heat and sultriness are forecast to qualify as “extreme” and “rare,” ranking a 4 on the 1-to-4 hazard scale on the National Weather Service’s experimental “HeatRisk” scale.

Similarly, Sunday is expected to rank as “extreme,” the highest level on the three-tiered “heat ranking system” developed by Applied Climatologists Inc., said company president Laurence Kalkstein, a climatologist and heat-mortality specialist. The “extreme” level continues Monday on the Kalkstein scale, given the steamy morning temperatures.

Kalkstein helped Philly and the weather service develop heat-response programs in the deadly 1990s.

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

Federal officials have credited Philly’s heat wave-response system with saving lives. About 10 times as many people died of heat-related causes in the 10-year period ending in 2002 as have died in the last 10 years in total.

So far, no heat deaths have been reported this year.

After a cold front passes through the region, conditions should improve through the day Monday although a seventh consecutive 90-plus high is likely.

“The big thing on Monday will be the humidity coming down,” said AccuWeather meteorologist Ryan Adamson.

Tuesday, the high may not reach 90, but Wednesday is expected to be a virtual rerun of the stickiness that the region has experienced this weekend.

Friday, the humidity is expected to be “quite low,” he said, adding, “compared to what we’ve been through, it’s going to feel quite nice.”