In 1931, it was this hot in September in Philly, and no one had air-conditioning

The nation had other issues on its hot plate that year. More than 2,200 banks failed, and it is estimated that businesses closed at the rate of 133 a day. Fully one-sixth of the American workforce was unemployed.

And as an all-time climate upheaval was brewing in the Great Plains back in 1931 with the onset of the Dust Bowl droughts, weather was making major news that September from the Rockies to the East Coast.

A hot spell impressive for its tenacity and areal coverage set temperature records in Huron, S.D.; Moorhead, Minn.; Detroit; Baltimore; and, yes, Philadelphia.

For Philly, it was the last time that the city experienced a six-day September heat wave — defined as at least three consecutive days of 90-degree highs. The temperature hit a record 97 for the date on Sept. 11 that still stands.

This hot spell is likely to match 1931′s for duration, with the heat due to continue through Friday, said Eric Hoeflich, meteorologist with the National Weather Service Office in Mount Holly. But it probably won’t survive the weekend.

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On Wednesday, the high reached 95 degrees at Philadelphia International Airport, tying the record for a Sept. 6, first set in 1983 and again in 2018. The record for a Sept. 7, however, appears safe: That would be 102, in 1881, several degrees above Thursday’s forecast high.

That 1931 heat wave was particularly notable in that it came later in the month — when the days were rapidly shortening — than this one.

It did not begin until Sept. 9, then picked up steam on the 11th.

The Inquirer’s coverage reported that some Pennsylvania schools decided to close, but not a peep about Philly’s.

The Associated Press reported one death in the city in the September hot spell of 92 years ago. But it is safe to say that no one could reliably estimate how many people were dying from the heat in those days, said Laurence Kalkstein, a climatologist who helped the city launch its heat-response plan in the 1990s.

» READ MORE: Philly's decision on counting heat deaths may have save thousands of lives

In 1931, no one, or almost no one, had air-conditioning, although prototypes were in the works.

Health officials have credited Philadelphia’s heat-response system with helping to reduce heat-related fatalities across the nation — the city has reported only one so far this year — and it happens that the city also was instrumental in the development of air-conditioning.

» READ MORE: Philly had an important role in the air-conditioning revolution

In 1923 it was the venue for the installation of Willis Carrier’s breakthrough invention, the “centrifugal chiller,” at the Stephen F. Whitman candy company plant. That’s where they made those “Whitman Sampler” chocolates, and where heat was the enemy.

The chiller, a critical building block for future systems that would cool, filter, and wring moisture out of indoor air, constituted Carrier’s “single most influential innovation,” according to the company history.

Two years later Carrier persuaded the Rivoli Theater in New York City to install one of his cooling units, the impetus for turning movie houses into mass cooling centers featuring “summer blockbusters.”

It took awhile for the cooling movement to reach American homes, but once it did, it was unstoppable, even though it did meet with some early resistance. Said Abeer Saha with the Smithsonian Institution’s National Museum of American History. “People were just used to being hot in the summer.”

And when window units first went on the market in 1932, the costs were prohibitive. Besides, this was the Depression.

But a more compact and affordable version eventually became available, and in 1947 about 43,000 were sold.

By 1973, about half of U.S. homes had air-conditioning, and these days that figure is closer to 90%, according to the Energy Department.

You can expect to hear the hums of air-conditioners at least through Friday, with highs in the record-challenging mid 90s on Thursday, before backing off a few degrees.

A front approaching the region is expected to set off showers and thunderstorms on Saturday, keeping the highs in the upper 80s and preventing this from becoming the longest September heat wave on record.