PORTLAND, Maine — The temperature soared to 100 degrees on Friday in Portland for only the fourth time since records have been kept as oppressive heat that gripped the Midwest moved to the nation’s northeasternmost tip, a region where many homeowners don’t even have air conditioners in their homes.

It was the first time the city hit triple digits since 1975, according to the National Weather Service, and the 100-degree reading broke the record for the date of 94 set in 1994 and the all-time high of 99 for the month.

The temperature in Bangor hit 97 degrees, according to preliminary reports from the weather service, breaking the July 22 record of 95 degrees, established in 1926.

“It’s pretty darned hot,” said Margaret Curtis, a weather service meteorologist based in Gray.

Temperatures reached 91 in Millinocket, 87 in Houlton and 82 in Caribou.

The temperature briefly hit 101 in Portland, but it didn’t stay long enough to account for the official record, Curtis said.

Either way, it was just shy of the hottest temperature ever recorded in the city: 103 degrees on Aug. 2, 1975.

Across the region, people sought refuge in air-conditioned offices, or fanned out in search of beaches or other places to cool down.

James Maxim didn’t expect the scorching heat as he and family members spent the week in Limington. By Friday, he’d had enough, fleeing the smoldering vacation home and hopping into the Saco River, where he found some relief even though the water was freakishly warm.

“There’s only so many cold beverages you can drink before you have to jump into something,” said Maxim, 33, of Lunenburg, Mass., after sitting recliner-style on smooth rocks as the water washed over him.

It was hot across the region. It also hit triple digits in Manchester, Concord and Portsmouth in New Hampshire.

The temperature was expected to hit the 90s again on Saturday in Portland, which would meet the National Weather Service’s definition of an official heat wave. Things will cool down on Sunday after a cold front moves through, bringing the high down to 78 or 80.

As the temperature climbed Friday, a power line failure knocked several power substations out of commission, leaving 13,000 Central Maine Power customers without electricity from Scarborough to Saco.

It couldn’t have come at a worse time for Funtown/Splashtown USA in Saco. The water and amusement park had to send several thousand guests packing on the hottest day of the summer.

Thankfully, no one was stuck on roller coasters or other rides.

“Horrible timing. Couldn’t be worse,” said Ed Hodgdon, sales and marketing director, noting that guests were given vouchers to return on another day.

The entire urban Northeast baked like a potato wrapped in foil as record-breaking, temperatures and steam-bath humidity combined with the heat-trapping effects of asphalt and concrete to make millions of people miserable.

The mercury in Newark, N.J., reached 108, the highest temperature ever recorded in the city. Airports near Washington and Baltimore hit 105. Philadelphia reached 104, Boston 103, and Providence, R.I., 100. New York City hit 104 degrees, just 2 short of its all-time high, and with the oppressive humidity, it felt like 113.

Donald Demarque, a handyman, sat outside an auto repair shop in the broiling Bronx, waiting to get the air conditioner checked on his Nissan.

“It’s only working at about half power,” he said. “I think if it was a regular day I could put up with it, but not today. Today you don’t want to have the car windows open.”

In Baltimore, a homeless Dale Brown said he buys a $3.50 day-pass to ride the commuter rail system to stay cool — and sober.

“I’m surprised more homeless people don’t do that,” he said. “That kills a lot of the day. One more day successful without drinking.”

An old prison in Cranston, R.I., had to bring in portable air conditioners, fans and cold water for the 100 inmates on a cellblock with a broken air-conditioning system.

In Philadelphia, 50 of the city’s 70 pools operated on 45-minute cycles to give everyone a chance to get in. Some New Yorkers were unable to take a dip to cool off at some beaches in Brooklyn and Staten Island after millions of gallons of raw sewage spilled from a wastewater treatment plant.

The heat wave wafted in from the Midwest — it began last weekend and did not break until Friday in Chicago — and is a suspected or confirmed cause in more than a dozen deaths around the country. On Friday, the medical examiner’s office in Chicago listed heat stress or heatstroke as the cause of death for seven people. An 18-year-old landscaper who died Thursday night in Louisville, Ky., had a temperature of 110, the coroner said.

Jake Crouch, a climatologist at the National Climatic Data Center in Asheville, N.C., said the heat wave is taking its place in duration alongside deadly hot spells in 1988 and 1995 that lasted a week or more.

On Friday, power supplies were stretched, and utilities were hoping that some businesses would close early for the weekend.

Con Edison in New York set a record for power demand at 1 p.m., breaking a mark set Aug. 2, 2006, utility spokesman Bob McGhee said.

Several hundred homes and businesses were hit with blackouts, but power was restored by midafternoon. Voltage was deliberately reduced in several neighborhoods in the city and suburbs to keep underground cables from overheating; McGhee said customers wouldn’t notice.

The electrical grid that serves 13 states, mostly in the Mid-Atlantic region, set an all-time record Thursday for power usage.

Dangerous-heat advisories and air quality alerts were sent out for most of the Northeast on Friday. Richard Ruvo, section chief in New York for the Environmental Protection Administration, said: “Today is a very bad day.”

“When there’s more power demand, there’s more power plants running, and there’s more pollution. We’re seeing ozone levels above unhealthy levels in the entire Northeast and Midwest, not just in the cities,” he said. “On days like today, the air quality affects everyone, not just asthmatics and the elderly.”

Lauren Nash, a meteorologist with the National Weather Service, said the cities are experiencing the “urban heat island” effect.

“All the concrete and the blacktop warms up faster, so it keeps the city hotter and it stays hotter longer,” she said. Overnight temperatures did not get below 80 in some areas.

Richard Karty, who teaches urban ecology at the New School in New York City, said, “If one urban area is next to another urban area, like New York and Newark, it’s just going to compound both the heat and the air pollution.”

Dayana Byrnes, 21, of Waldorf, Md., learned something new about herself as she worked outdoors in Washington to promote a website with free bottled drinks.

“I didn’t think legs could sweat,” Byrnes said.

In Manchester, Conn., the fire department sent out a vehicle to distribute cold water to road crews.

Horse races were canceled at several tracks.

But hundreds of people who lined up outside the Izod Center in Newark to audition for NBC’s “The Voice” were undeterred. And in Manassas, Va., Civil War buffs said the weather — perhaps 20 degrees hotter than in 1861 — would not prevent a 150th anniversary re-enactment of the Battle of Bull Run.

George Alcox, 58, of Berea, Ohio, said the wool uniforms and muslin undergarments the re-enactors wear are “not as hot as they look.”

“They’re hotter,” he said.

The Bangor Daily News and Associated Press writers Jim Fitzgerald in New York, Matthew Barakat in Manassas, Va., Laura Crimaldi in Providence, R.I., Maryclaire Dale in Philadelphia, Alex Dominguez in Baltimore, Samantha Henry in Newark, N.J., Karen Matthews in New York, and Randy Schmid and Jessica Gresko in Washington contributed to this report.