Near record-breaking heat will give way to steamy encore: Sunday will be like Saturday, only worse.

Research has linked violence to hot weather, and on Saturday, as the heat index crept toward 110 and the air felt like water-vapor consomme, quite the skirmish erupted in Fairmount Park involving some sophisticated weaponry.

In this case, however, no deaths or injuries were reported. The most potent weapon was a Super Soaker, and some of the 100 or so participants came away about as wet as the swimmers in the nearby Kelly Pool.

If Gabriel Nyantakyi, founder of Waterarms over Firearms and the organizer of this “WaterFight Philly Remix” event, had any complaint, it was that the heat was a shade too extreme. “It can be oppressive,” he said, “not ideal for outdoor activity.”

The official high at Philadelphia International Airport was 97, just shy of the record, but the heat index maxed at 109, said Jonathan O’Brien, a meteorologist at the National Weather Service in Mount Holly.

Those who went to the Shore evidently packed the heat with them: The official high of 99 set a record in Atlantic City. O’Brien said showers well to the north of the area or a wayward breeze might have kept the temperature in Philadelphia from hitting triple figures for the first time since 2012. The thermometer did reach 100 at Northeast Philadelphia Airport, where the wind direction was slightly different.

However, the official high for Philadelphia will make another run at 100 on Sunday — with a heat index of up to 111 — and the morning low is likely to set a record for the date for highest minimum temperature, a symptom of the oppressive humidity engorging the atmosphere. Water vapor slows the cooling at night by keeping daytime heat from radiating into the atmosphere.

The weather service’s “excessive heat warning” remains in effect until 11 p.m. Sunday.

Excessive heat is exacerbated by the “urban heat island effect” as buildings and paved surfaces absorb heat and slacken winds. Heat warnings are more common in urban cores than elsewhere, but this warning covers all of New Jersey and almost the entire eastern half of Pennsylvania as high pressure off the Atlantic Coast bathes the region with sultry subtropical winds.

The Philadelphia Corporation for the Aging will operate its Heatline (215-765-9040) from 8:30 a.m. until midnight Sunday. As of Saturday, it had fielded 441 calls, said PCA spokesperson Shannon Reyes.

The heat wave might have had a greater impact, particularly on power companies, had it ripened and peaked during the workweek, when office buildings would be running air-conditioning systems full throttle. Peco, for example, reported only about 1,400 outages on Saturday.

But among the victims were Donna and John Gates.

At 5:30 p.m. Saturday, some 12 hours after they got an alert that the alarm was going off at the Rita’s Italian Ice store they own at 16th and Spruce Streets, in Center City, the Mount Laurel couple were finishing a costly purging of product ruined by an outage.

In the trash went 15 5-gallon tubs of water ice, cartons of frozen custard, and all other dairy products, along with boxes of frozen pretzels.

“I’m upset we have to throw so much away,” said an exasperated Donna Gates.

There’s no telling how much water ice and custard they would have sold on such a sweltering Saturday, but Friday’s sales exceeded $2,200, said Gates’ daughter, Danielle DiBartolo, also of Mount Laurel, who is one of the store’s managers.

As the family locked up for the day, they were already trying to put the day’s loss behind them. “We regroup tomorrow. We regroup and start over,” Donna Gates said.

By Monday, O’Brien said, the heat should ease as a “strong but slow-moving” cold front approaches, setting off heavy showers that could lead to some flooding late Monday and Tuesday. Ultimately, however, that front will broom away the heat and humidity, setting up a sequence of fabulous days starting Wednesday.

Next weekend, the forecast calls for sun and temperatures in the upper 80s, actually closer to the weather that Nyantakyi had envisioned when he scheduled WaterFight Philly a few weeks back.

That’s what the July 20 forecast had called for back then, but as O’Brien and his colleagues are well aware, these things can change.

Nyantakyi said that some of the participants came by public transportation and he was concerned about the discomfort they might endure waiting for buses. Everything went well, however, and the event drew a crowd ranging in age from 3 to 60.

The 36-year-old West Philadelphian said that he grew up with the Super Soaker — invented by an African American, Lonnie Johnson — and it literally was a game-changer. “It definitely changed the way we played,” he said. “We had cap guns. Everything we did was rat-tat-tat.” He said he has owned about 100 Super Soakers at various times.

Waterarms over Firearms is his way of taking aim at gun violence. In explaining the organization’s name, he said, “The firearm is destructive; to just call it a gun isn’t enough.” Waterarms? “This is a gun that was created with a different intention and purpose.

“I want to shift the culture and people’s imaging out what guns can be.”

However oppressive it might have been on Saturday, Mary Tillery, 60, of North Philadelphia, said the trek to WaterFight Philly was worth it.

“I’m so glad I came out,” she said. “This wasn’t on my bucket list and now it is.”

Inquirer staff writer Tyger Williams contributed to this article.