It’s as if Mother Nature knows when the calendar is officially turning to fall.

Right on schedule in the Boston area, it’s going to flip from summer-like temperatures over the weekend to autumn-like temps as the first day of fall approaches this week. Temps on Monday should drop into the 60s.

“We’ll have cooler conditions on Monday across eastern Massachusetts as a backdoor cold front comes through the region,” Matthew Belk, meteorologist at the National Weather Service’s Boston office, told the Herald.

Meanwhile, as the backdoor cold front stalls across southern New England, some much-needed rain showers and scattered thunderstorms are expected to develop Monday afternoon. The region is still facing a severe drought, so any rain is welcomed.

A few lingering showers and thunderstorms could last into Tuesday before things dry out. Temps on Tuesday should remain in the mid-60s.

Then the pick of the week will be on Wednesday with partly sunny skies in the low 70s. Another round of showers and thunderstorms is possible Wednesday night into Thursday ahead of a strong cold front.

The coldest air of the season so far will arrive Friday just in time for fall, with high temps struggling to get out of the 50s. So the first full day of astronomical autumn will feel like fall.

“We’ll have a significant cool down Friday into the weekend,” Belk said.

Ahead of the start of fall, Hurricane Fiona is gaining steam near Puerto Rico, and could impact the East Coast by the end of the week. Fiona may produce 12 to 16 inches of rain, possibly up to 25 inches, over portions of Puerto Rico — triggering extreme life-threatening flooding risk.

The National Hurricane Center reported that “catastrophic flooding” is expected.

“There will probably be some rough surf here,” Belk said about the local Cape Cod impacts. “We’ll have to see what swells it will generate, but there will most likely be rough seas at beaches as we get into the later part of the week.”