100 degrees possible Monday as Philly weather takes a ‘dangerously hot’ turn; heat warning issued

While the summer of 2020 appears to be on its way to being one of the warmer ones in the period of record in Philadelphia, so far the region has avoided the extreme heat that has baked other parts of the nation. But it looks like it’s our turn.

The National Weather Service warns that the next several days — particularly Monday, when the daytime high in Philadelphia could make a run at 100 for the first time in eight years — could be “dangerously hot” and that the heat wave could continue into next weekend.

“It’s going to be a just awful heat wave,” said Brett Rossio, a meteorologist with AccuWeather Inc. “You may even knock out 100.” Ironically, the only thing preventing that from happening would be all the moisture in the air, which will divert some of the sun’s energy but will drive up heat indexes. The record for the date is 99, set in 1930.

Heat waves are local perennials, but this one would be occurring during a stubborn pandemic. The coronavirus and concerns about its spread likely is going to be a complicating factor in opening and operating cooling shelters.

Camden County is confronting “unprecedented challenges,” said spokesperson Dan Keashen. He said local emergency management officials are ready to move people to cooling centers if necessary.

» READ MORE: With summer forecasts calling for dangerous heat, pandemic is clouding Philly’s response plans

“Hopefully people can do something to cool themselves,” said Lee Robertson, a meteorologist with the National Weather Service. “Hopefully, everyone will be checking on family and their neighbors.”

The weather service has posted an “excessive heat warning” for the entire region — save for Upper Bucks Count, which was under a “watch” — from noon Sunday afternoon into Monday evening, with the potential for heat indexes hitting 110.

Often those warnings are confined to the urban corridor. However, this one includes even Chester County horse country and far northern Montgomery County.

Monday’s heat will come after after an oppressive overnight night when it might drop below 80, said Rossio. Highs are forecast to reach the mid-90s Saturday and Sunday.

» READ MORE: Inga Saffron: Philadelphia struggles to adapt summer’s rituals to pandemic’s reality

Chris Gallagher, director of the Philadelphia Corporation for Aging’s helpline call center, said the phone lines will be staffed starting Sunday if needed. The number is 215-765-9040. During heat waves, the center can field as many as 400 calls a day.

Each day will bring a chance of afternoon showers, Robertson said, but the nights are going to be so steamy that the days are going to heat up in a hurry.

The region has had a run of good fortune this summer as it has escaped prolonged heat waves, even as temperatures have averaged about 2 degrees above normal.

» READ MORE: Summers are hotter, but heat-related deaths have dropped. Philadelphia has a lot do with that.

Previous heat threats that showed up in computer models were sabotaged by the chaos of the atmosphere that is the mortal enemy of longer-range forecasts. Those “ring of fire” thunderstorms on July 6 not only put dents in rainfall deficits, they snuffed out the first heat wave of the season, which was in its fifth day.

So much for that good fortune. The system primarily responsible is high pressure centered off the Atlantic Coast that is a prodigious exporter of hot, vapor-rich air. Areas to the west of high centers experience winds from the south as part of their clockwise circulation.

This heat wave has staying power, said AccuWeather’s Rossio. “In terms of 90-degree weather, it’s going to be a while,” he said. “You’re not out of the woods until Thursday,” when the highs should crest in the upper 80s. Next weekend should be considerably more comfortable.

If you can’t stand the heat, stop reading.

The government’s outlooks for the rest of the month favor continued heat, as does its forecast for August.