Scorching heat and suffocating humidity are expected to make for a sweltering weekend in Massachusetts, threatening temperature records and sending energy-sapped residents and midsummer tourists to beaches and air-conditioned rooms for relief.
For both Saturday and Sunday, temperatures in the high 90s are predicted to combine with oppressive humidity in a double-barreled assault on anyone who ventures outdoors for long.
Emergency officials warned that the effect could be life-threatening, particularly for the elderly and those with medical conditions.
The National Weather Service, which issued an excessive heat warning for most of the state, said temperatures could shatter the Boston records of 99 for July 20, set in 1991, and 102 for July 21, set in 1977.
“When temperatures rise this high, and especially with humidity as high as it’s expected, we start worrying,” said Dr. Brian Yun, associate director of clinical operations for Massachusetts General Hospital’s emergency department.
“Whether you’re an athlete who thinks that they’re acclimated to the weather or a child or an elderly person, we’re all at risk for heat-related illness,” Yun said.
The thermometer will tell only part of the sizzling story. The humidity, with weekend dewpoints expected in the sultry mid-70s, should make the air feel several degrees hotter, possibly as high as 110 and above in some places.
The heat index, which measures that combined effect, was expected to peak Saturday in Eastern Massachusetts and parts of the Connecticut River Valley. Forecasters predicted that Cape Cod and the islands would escape the worst.
Heading north won’t provide much relief. Temperatures in Concord, N.H., are expected to be in the mid-90s Saturday with a heat index of 104, according to meteorologist Alan Dunham of the National Weather Service. In Portland, Maine, the thermometer should reach the upper 80s with a heat index of 100.
Around the region, preparations by hospitals, municipal officials, first responders, and utility companies ramped up Friday. Residents were cautioned to stay indoors, keep hydrated, and check on neighbors.
Boston Mayor Martin J. Walsh declared a heat emergency that began at noon Friday and will extend through Sunday evening. Cooling areas are available at 35 of the city’s Youth & Families centers, and public pools will be open free of charge.
The city also is increasing outreach to the elderly and homeless, including added checks on the most vulnerable. An advisory from the Massachusetts Emergency Management Agency urged residents to check with local authorities or call 2-1-1 to find cooling centers and shelters.
Mass. General will have fans, water-spray bottles, and ice-water baths ready.
“What we’re trying to do is get the message out to everyone all over the state to be careful,” Yun said.
The rise in temperatures comes as a high-pressure system, and hot air and humidity from the Southeastern United States and Gulf of Mexico, arrived in the region. The weather is giving Massachusetts a taste of the heat that has enveloped much of the country, according to the National Weather Service.
Improvement is expected Monday, when temperatures will drop into the 80s.
The prospects of an uncomfortable weekend were on the minds of many Friday as the mercury began rising.
Ivette Collado, a native of the Dominican Republic, treated herself to a stick of chocolate-covered vanilla ice cream as she walked toward South Station in Boston to catch a train home to Attleboro.
“I have to be careful with myself because I get dizzy. I get headaches really easily,” Collado said. “I’ll try to go to the beach a little bit, if I can, with my daughter.”
Steven Jenkins of Cambridge, walking in the Financial District, said he and his girlfriend will head to Cape Cod and Martha’s Vineyard to escape the heat.
“I’ll spend some time on the beach. It’s still going to be sunny,” said Jenkins, 28. “We’ll probably do a little bit of shopping, grab some great food on Martha’s Vineyard.”
At Carson Beach in South Boston, David Schiemer tested an inflatable neon green kayak that he had just bought.
“I’m just going to hang by the beach, stay by the water, and enjoy some water sports,” said Schiemer, a 28-year-old mechanical engineer.
Nearby, Larinda Cole sunned herself in a chair at M Street Beach.
Cole, a career coach at Babson College, lives in West Roxbury but is originally from Virginia, where she became accustomed to 100-degree weather during the summer.
Cole said she’s mastered a hot-weather routine.
“I’ll enjoy the little bit of sun in the beginning of the morning, stay indoors during the hottest. Maybe go to an indoor mall . . . do some window shopping, see a movie,” Cole said. “Evenings, I’ll probably go to some restaurants with friends. Seafood is complementary to this weather right now.”
Fang Li, of Sharon, also said she has lived in many hotter places than the Boston area.
“It’s never gotten to a time when it was really, really hot,” said Li, 47, who endured Chinese summers without air conditioning.
“I lived in Georgia before I moved here, so I know what it could be. The heat could be much hotter. Before that I was in Minnesota, and Minnesota could get really humid and hot. So this is not really that bad,” Li said with a laugh in Downtown Crossing.
“Worst case, we have air conditioning, and the best thing is that we have a basement,” she said. “The basement is really cool.”
Li said she might take her two sons, 16 and 14, to the YMCA so they all can enjoy the swimming pool.
Amy Mangiafico, 49, of Danvers, sat unfazed in the lunchtime sun Friday. Over the weekend, she said, she probably will head to the state beach in Salisbury.
“I love the heat. It doesn’t get to me,” Mangiafico said in Liberty Square. “You adjust to any and all conditions.”