Valentine’s Day in Boston was the coldest on record for more than 80 years, as temperatures plunged to levels that could even keep an intrepid Cupid indoors.

Sunday morning, the temperature plummeted to minus 9, with a windchill of minus 36, shattering the record by 6 degrees. Before Sunday, the coldest Valentine’s Day recorded in Boston rang in at minus 3 in 1934, according to the National Weather Service in Taunton.

“It’s extremely rare to get this cold in Boston,’’ said Hayden Frank, a meteorologist at the National Weather Service.

Temperatures across the state were below zero at daybreak Sunday, with wind chills in some areas down to minus 40 or more.

But relief is around the corner.

Monday, temperatures are expected to rise to near-freezing levels with the possibility of snow, and Tuesday, temperatures may climb into the 50s, accompanied by wind and rain.

Over the weekend, the arctic-like weather prompted outreach teams of trained professionals to canvass the city for people without shelter. They brought in dozens of homeless men and women from the streets.

Pine Street Inn, one of New England’s largest homeless shelters, said the record-breaking temperatures meant its facilities were housing hundreds more than usual.

Barbara Trevisan, a spokeswoman for the nonprofit, said the shelter helped treat two people with frostbite, one of whom had to be taken to the hospital.

Boston’s homeless shelter providers keep a list of people they know are on the streets, and workers go out during hazardous weather and actively encourage them to come indoors, Trevisan said.

“There were about 10 people who rarely come in, who came in and that was pretty huge,’’ she said. “It’s pretty intensive work.’’

Che Knight, a spokeswoman for the city’s public health commission, said the agency’s street teams reached 30 individuals who usually opt to stay outside.

Knight said the city’s shelters, already operating at maximum capacity, continued to admit people throughout Sunday.

“All of the shelters have been full and staff are encouraging guests to not go outside today,’’ Knight said in a statement.

Despite the pleas from public safety professionals, however, Michelle Carnazzo-Amoroso of Revere decided to brave the frigid conditions. Carnazzo-Amoroso, who told the Globe on Saturday afternoon of her intentions to remain outside through the night, said she stuck to her plan.

“I just stayed outside,’’ Carnazzo-Amoroso said. “Things were all right.’’

On Sunday afternoon, she was back to her usual place near the Park Street MBTA stop. Carnazzo-Amoroso has been homeless for two years.

“Yesterday was a little worse than usual,’’ Carnazzo-Amoroso said. “But Tuesday it’ll be 50, so that’ll be nice.’’

Terri Ramirez and Jason Martin, a married couple homeless their entire adult lives, said they stayed at Pine Street Inn last night — reluctantly.

“They forced us in,’’ said Ramirez, a 53-year-old woman from El Paso, Mexico.

Her husband was disappointed. To enter the shelter, he said, the two had to leave some possessions behind.

Myra Ackerman, a program manager for homeless families who works for FamilyAid Boston, said the full impact of the weekend’s bitter cold on the homeless population may not be known for days.

“There’s much more homelessness than people know,’’ Ackerman said. “We’ll see how it goes.’’

Sunday morning, the MBTA’s Red, Orange, and Green lines experienced moderate to severe delays due to mechanical problems and rails cracking under “arctic-like conditions,’’ said MBTA spokesman Joe Pesaturo. But by 2 p.m., the problems had been fixed.

“MBTA personnel worked very hard all night on preventative measures, but the coldest morning in decades has had an impact on aging vehicles and infrastructure,’’ Pesaturo said.

At Logan International Airport, some passengers experienced moderate delays, while others had to wait for hours to board flights.

Michelle Hoffman of North Carolina was stuck at the JetBlue terminal Sunday afternoon as she waited to return from a snowmobiling trip.

“We’re four-and-a-half-hours delayed,’’ she said.

In Lynn and Saugus, more than 14,000 customers lost power over Saturday night into Sunday morning, according to the Massachusetts Emergency Management Agency power outage website.

One Lynn resident, 48-year-old Chris Conrad, said he woke up in a frigid house at about 8 a.m.

“We woke up, it was 46 degrees inside the house and with below-zero temperatures outside, so that’s not good,’’ Conrad said. “The whole house was freezing.’’

By afternoon, Conrad’s power had been restored, as had the power for most residents.

Anyone hardy enough to venture along the ocean’s edge Sunday got to see beautiful tendrils of “arctic sea smoke’’ over the water, caused by the very cold air hitting the warmer ocean water.

“That cold air over the warmer water goes ahead and condenses some of the water vapor evaporating over the water, and that gives you your arctic sea smoke,’’ said meteorologist Alan Dunham with the National Weather Service.

But the cold air arriving on Valentine’s Day caused problems for florists like David Levine, the owner of Central Square Florist in Cambridge.

He and his staff prepared more than 200 deliveries by adding extra wrapping for the flowers, and beefing up delivery crews.

“Last year, we had the snowiest Valentine’s Day in a hundred years,’’ Levine said, referring to the barrage of snowstorms in early 2015 with record-setting accumulations. “And this day, we got the coldest day in a hundred years.’’

Globe correspondent Alexandra Koktsidis and Aimee Ortiz of the Globe staff contributed to this report. Nicole Fleming can be reached at nicole.fleming@globe.com. Astead W. Herndon can be reached at astead.herndon@ globe.com. Follow him on Twitter @AsteadWH.