Summer is starting earlier. Massachusetts is not prepared.

Natalie Santos-Castillo, manager of Family Hardware on Blue Hill Avenue, arranged room and window fans on a shelf in Dorchester.John Tlumacki/Globe Staff

Officially, summer doesn’t start for another month, but you’d never know it from this weekend’s scorching forecasts. On Saturday and Sunday, roughly half of the country will be blanketed by a sweltering heat dome. Temperatures could climb above 90 degrees in Boston, with a real-feel forecast of over 95 degrees on both days.

The weekend’s weather will bring Boston’s “first widespread significant heat and humidity” of the season, according to the National Weather Service. Temperatures could set local daily and monthly records.

When compared with historical temperature data, these figures are outliers. But as New England warms thanks to the climate crisis, summer-like temperatures in May are becoming the new normal — and local institutions and cultural practices are struggling to keep up.

“One of the most dangerous problems we have in New England is that people don’t think of this area as a hot area,” Bianca Bowman, climate justice organizer at the environmental justice organization GreenRoots, said.

This early in the season, when temperatures historically were much cooler, most pools and beaches are still without lifeguards. University commencements are staged in un-air-conditioned arenas. People haven’t lugged fans out of storage, never mind put air conditioners in the windows.

Caught unprepared, some were racing Friday to buy AC units while hardware stores were still stocked. Roxbury resident Veronica Williams, 58, went to the South Bay Home Depot to buy one for her mother, who has chronic obstructive pulmonary disease.

“She’s 81, elderly, and [with] the heat wave coming, I want her to be comfortable and nice and cool, so she won’t have trouble breathing,” Williams said. “When it’s really, really hot, the air is thick, and I just want her to be comfortable.”

Rachel Licker, principal climate scientist at the Union of Concerned Scientists, said the weekend’s heat is a clear hallmark of the climate crisis, and that without urgent action, even higher temperatures are in store.

The Clougherty pool is empty of water and locked up as people will be looking for ways to stay cool over the hot weekend. John Tlumacki/Globe Staff

”This kind of hot weather is exactly what climate change has in store for New England, especially if we do not get our act together as a nation and ramp down heat trapping emissions,” she said.

Outdoor workers, the elderly, children, and those with respiratory and cardiovascular disease are at higher risk, she said.

“It’s critical that people check in on elderly neighbors or family members, as well as those with disabilities to make sure they able to keep safe,” she said.

AC units can be a lifesaving cooling measure, though they also contribute to the climate problem by spewing out planet-warming pollution. They can also put extra stress on the electricity system. But Matthew Kakley, a spokesperson for the regional grid operator ISO-New England said he didn’t expect any outages due to increased demand over the weekend.

“The relatively short time frame of hot weather ... serves to keep demand levels down,” he said.

Window air conditioners can be hard to afford for some people, both the upfront expense and the cost of running them. That’s especially true for low-income residents, who also disproportionately live in heat islands — areas where abundant concrete and asphalt soak up the sun’s rays and radiate excess heat, driving up the cost of staying cool.

Bowman, the environmental activist, will spend Saturday at a women’s wellness fair in Chelsea, helping residents to advocate for changes that can help them weather the heat, such as cooling centers and tree coverage.

The Rev. Vernon K. Walker, senior program manager of Communities Responding to Extreme Weather, or CREW, plans to spend Sunday at St. Stephen Episcopal Church distributing water and other materials, along with staff from Massachusetts General Hospital, to help residents stay cool and hydrated, and also will raffle off energy-efficient air conditioners.

He noted that in the United States, heat waves are the deadliest form of extreme weather, especially for poorer people, communities of color, and others who have fewer resources to stay cool when they strike.

“We should treat heat with the seriousness that it deserves,” he said.

Cities and towns scrambled to help keep residents cool. In Boston, Mayor Michelle Wu announced the city will open 15 cooling centers at Boston Centers for Youth & Families community centers on Saturday and Sunday from 9 a.m. through 5 p.m., and more than 50 splash pads will be open at parks and playgrounds.

The city will also open some community centers’ indoor pools on Saturday, which residents can use if they register ahead of time.

In Plymouth, the splash pad inside Nelson Memorial Park on Water Street will be open all weekend; its public library’s main location and Manomet branch will also be open on Saturday, officials said.

In Brookline, officials are opening water play areas for children at 13 parks earlier than usual. Canton and Hingham are using their libraries as cooling centers, while in East Bridgewater residents can visit Town Hall, which will be staffed by Community Emergency Response Team volunteers, officials said.

But many public pools in Massachusetts still don’t open until early June or even later — a relic of years past, when heat waves in May were exceedingly rare. At most ponds, lakes, and beaches, lifeguards remain in short supply — a concern in late spring, when hot weather, cool water, and unsupervised waterfronts can make swimming dangerous.

Plymouth officials — who warned that there would be no lifeguards on duty until Memorial Day — cautioned residents that despite the heat, cold water temperatures “can incapacitate a person quickly should they unexpectedly fall into the water.”

Carolyn Assa, a spokeswoman for the state Department of Conservation and Recreation, said there would be no lifeguards this weekend at any of the state’s more than one dozen public beaches, where staff are not posted until Memorial Day weekend each year. Assa said, though, that the state is opening 15 spray decks to the public on Saturday, a week ahead of the season, to help children and families cool off.

Houghton’s Pond in Milton, where a 39-year-old Quincy father drowned last year, won’t have lifeguards until next Saturday, according to the DCR. And, until next weekend, no lifeguards will be on duty at Crane Beach in Ipswich, where a 24-year-old man drowned last year, or at any other beaches operated by the Trustees of Reservations, spokesman Aaron Gouveia said.

Colleges and universities prepared to hold graduation ceremonies as usual, in spite of the heat. This weekend, students are set to walk the stage at colleges across the area, including Boston University, Brandeis in Waltham, and Tufts in Medford.

At Salem State University. Elisa Castillo, associate dean of students for wellness, said the COVID-19 precautions the school has in place will likely help guests at its graduation festivities beat the heat.

To encourage social distancing, the school is hosting five small ceremonies instead of three larger ones, so its un-air-conditioned Rockett Arena will only hit a maximum 75 percent capacity. Attendees can also opt to watch the celebration via livestream.

Joey Wolongevicz is graduating Saturday from Salem State with a bachelor’s degree in geography. Having spent four years learning about climate change, he says graduating in such extreme temperatures is the “cherry on top.”

“To have the actual ceremony where I get my degree be during a heat wave,” he said, “it’s kind of poetic, I suppose.”

Correction: Because of incorrect information supplied to the Globe, an earlier version of this story misstated the field in which Salem State University student Joey Wolongevicz is receiving a degree. Wolongevicz studied geography. The story also included an incorrect date for lifeguards returning to Houghton’s Pond. The lifeguards return on May 28. Additionally, the story did not mention that the DCR was to open 15 spray decks on May 21, a week early.