PGA golfers and regatta rowers can expect a weekend warmup. Then a heat wave is possible next week.

One of the stranger runs of weather in the period of record is poised to resume its peculiar ways, but after a chilly, windy Friday, the atmosphere’s behavior during the weekend should be close to ideal for the PGA Championship at Aronimink and the annual Stotesbury Regatta.

A major warmup is due to begin Saturday and ripen into what may become the first heat wave of the year, forecasters say, with temperatures possibly reaching 90 degrees or higher Monday through Wednesday.

That would occur a month after the readings reached 90 on an unseemly early date, only to be followed by a peach-and-apple-killing freeze.

If such swings were going to happen, the seasonal transition months of April and May would be the likeliest times, said Marc Chenard, a branch chief at the government’s Weather Prediction Center, in College Park, Md.

But, yes, he said, what’s happened this year has been “extreme.”

Meanwhile, precipitation deficits keep growing, even though measurable rain has fallen upon Philadelphia on 11 of the last 20 days.

Those brisk winds Friday probably weren’t on the wish lists of the golfers participating in the PGA Championship at the Aronimink Golf Club, but they shouldn’t be around the next two days, and highs are forecast to be in the 80s — 15 to 20 degrees higher than they were Friday.

Some showers will progress through Pennsylvania Saturday, “but it looks like they’re going to die off before they get to Philadelphia,” Chenard said.

On Sunday, “isolated” thunderstorms may prowl the region, said Paul Fitzsimmons, meteorologist at the National Weather Service Office in Mount Holly. However, “the chances are very low” for any given location, including Aronimink or the Schuylkill in Philly, where the regatta will take place.

As of Friday, May had averaged about a degree below normal officially, but nature is about to turn up the heat.

Chances are excellent that temperatures will reach 90 or better on Monday; Tuesday, Pennsylvania primary Election Day; and Wednesday. Daily records probably are safe: Philly’s all-time high of 94 degrees for May 18 was reached in 1962, as was the May 19 record of 96 degrees. Wednesday’s record of 94 degrees was set in 1996.

Fortunately, this hot spell is unlikely to be dangerous, since the humidity and dew point levels would be too low to set off the heat-advisory alarm bells, meteorologists said.

“We’ll get some moisture from the South, but it’s not going to be like summertime heat and humidity,” said Chenard.

One reason for the lack of mugginess has been the recent dryness, which also likely will be contributing to the heat.

The U.S. Drought Monitor on Thursday had the entire region in “extreme drought.” New Jersey is under a drought “emergency,” and Chester County is under a drought warning.

The dryness promotes heating since the sun’s energy isn’t diverted to evaporating moisture. But the lack of evaporation also helps hold down the mugginess that drives up heat indexes.

Officially, rain in Philly is about a third of normal this month.

It’s worrisome but not all bad, said Andrew Frankenfield, an agronomist with Penn State Montgomery County Extension.

For farmers who are busy planting, the dryness beats contending with mud.

Plus, “We had enough rain in the last month to keep things actively growing,” Frankenfield said, and the coolness has inhibited the drying-out process.

But gardeners should keep the hoses handy: No significant rain is in the extended forecasts.