So far, heat has been blamed for contributing to at least five deaths in the region since late May.
No new deaths were reported Thursday, but health officials remain concerned about the effects of the tenacious heat on the elderly and people with health problems.
An "excessive heat warning" remains in effect until 8 p.m. Saturday, and the Philadelphia Corp. for the Aging will keep its heatline - 215-765-9040 - operating until 8 p.m. Saturday.
Sunday will be less brutal, but the temperature is forecast to zip past 90 for an 11th consecutive day. That would represent Philadelphia's seventh-longest heat wave, defined as three or more days with daily highs of 90 or better, and the most prolonged in 13 summers.
"I'm sure the electric bill is going to show that," said Gary Szatkowski, meteorologist in charge of the National Weather Service in Mount Holly.
Sustaining a string of 90-degree days isn't easy, Szatkowski noted. Even with prolonged hot spells, an afternoon pop-up shower or a renegade onshore wind can interrupt the streak. That's not happening this time.
Heat is hardly a local phenomenon, as summer continues to blister the nation. July Fourth records were set at 108 stations, bringing the weekly total to 2,274, according to the National Climate Data Center.
"Even for the South, this has been nasty hot," said Alex Sosnowski, a meteorologist with AccuWeather Inc.
In tandem with the heat, dryness has spread rapidly. On Thursday, the U.S. Drought Monitor reported that more than 75 percent of the contiguous United States was in some state of drought, including Philadelphia and Delaware County.
Philadelphia's precipitation since Jan. 1 is about 30 percent shy of what it should be.
The next shot at thunderstorms arrives Saturday night with a heat-chasing front, but the cooler air will take the slow route from Canada. "This will kind of ooze in," said Sosnowski.
The temperature will crest in the mid-80s Monday, but by then, Philadelphia will have had its 17th day of 90-plus heat this year, indicative of a significant summer warming trend.
From 1874 through 1987, Philadelphia averaged 17 90-plus days for the entire warm season. Since 1988, the average has been 28.
That's a 65 percent increase.
Contact Anthony R. Wood
at 610-313-8210 or email@example.com.