The heat wave enveloping the Eastern Seaboard brought punishing record temperatures to the Washington region Friday, sending scores of people to emergency rooms with heat-related illnesses and closing down outdoor events.

The combination of heat and humidity produced a heat index in Washington of 121 degrees, the highest since July 1980. The suffocating conditions stemmed from a sprawling, moist tropical air mass — described as a heat dome or heat bubble — that reached the region Thursday and is expected to remain into Sunday.

The blistering weather forced the cancellation of summer events and children’s activities; some people even steered clear of public pools because they provided little relief.

Local authorities had reported no heat-related deaths, but at least 25 people nationwide have died in the heat wave.

On Friday, Dulles International Airport hit 105 degrees, the hottest there ever; Baltimore-Washington International Marshall Airport’s mark of 106 was its second-hottest daily temperature ever; and Reagan National Airport’s reading of 102 was one degree shy of its record for the date.

Diane Woods, a management and program analyst with the Internal Revenue Service, drank five bottles of water Friday morning but still wound up in the emergency room. Woods, 57, of San Diego, was touring the Mall but had to lie on the grass because she was so dizzy. She found a nearby police officer who called an ambulance to pick her up.

“I felt terrible and scared. My throat was constricting. I was very frightened,” Woods said in a telephone interview as she received an intravenous drip at Georgetown University Hospital. “I thought because I had so, so much water, that would take care of it. But didn’t help at all.”

In response to the heat, Metro made an exception to its no-drinking policy and is permitting travelers to carry bottles of water on trains, buses and in stations until the system closes Sunday night.

From Baltimore to New England, the band of heat drove temperatures into the triple digits. The Weather Channel reported that New York’s Central Park was 104 degrees Friday afternoon, the hottest reading there since 1977, and that the 104-degree reading in Atlantic City, N.J., was the hottest there since 1969.

Other cities reached all-time highs: Hartford, Conn., notched 103 degrees; Newark reached 108; and Boston, which hit 103, had its hottest day since 1926.

Saturday’s temperatures were expected to remain unforgiving, hitting as high as 103, which would surpass the record for the date: 101 at National Airport. One reprieve Saturday might come in the form of scattered thunderstorms in the late afternoon or evening, which could cool things down.

Hospitals around the region admitted patients with a array of heat-related illnesses. At Inova Loudoun Hospital, Ron Waldrop, medical director of pediatrics, estimated that 10 to 20 people arrived both on Thursday and Friday with signs of dehydration or heat exhaustion. Many complained of stomach ailments.

“You get a few days in the low 90s, then suddenly it jumps around 100, and you get a lot more sick people,” Waldrop said. “This may be the hottest time I’ve seen in Loudoun.”

By 3 p.m. Friday, Georgetown University Hospital’s emergency room had admitted six people with heat sickness. Many were simply given a liter of fluids, but extremely hyperthermic patients — anyone with body temperatures exceeding 101 degrees — were placed under large fans and sprayed with water.

“Most patients have been drinking water and doing a good job, but it’s not been enough to compensate for the extreme heat,” said Sanjay Shewakramani, a Georgetown emergency physician. “Many of the patients have been elderly, doing yard work or are security officers working outside, and most had prolonged exposure to the heat for at least a half-hour. One person had to be admitted after passing out and striking their head on the ground.”

Throughout the Washington area, activities were scrubbed or moved indoors. The National Park Service canceled outdoor events scheduled between 2 p.m. and 6 p.m. as part of Friday’s program commemorating the 150th anniversary of the Civil War Battle of Bull Run in Manassas because of excessive heat, officials said.

In Northern Virginia, organizers of the Bluemont concert series, typically held outdoors, moved this weekend’s shows — in Fredericksburg, Leesburg, Middleburg and Warrenton — indoors.

In the District, the more than 100 children’s camps sponsored by the city’s Department of Parks and Recreation canceled all outdoors activities from Thursday through the weekend, said John Stokes, the department’s chief of staff.

The nonprofit DC SCORES program canceled all soccer activities for its elementary school students. The children, who attend a soccer and arts camp, went to dance classes, visited a museum or a watched movie instead.

Middle school students at a soccer camp were permitted to play, but with precautions. Counselors set up tents, furnished plenty of cold water and orange slices, and mandated frequent breaks to go inside. Several children with asthma stayed home.

Even that old reliable antidote to all-consuming heat — the pool — wasn’t the draw it usually is. By midafternoon Friday, attendance at the city’s 18 public pools dropped to about 1,000, down from 1,200, Stokes said.

In Rockville, Regina DeCarlo and Amy Macomber scuttled plans to hit the pool with their kids. They opted for a seemingly cooler activity for their children, ages 6 to 10: Rockville Town Center’s splash fountain. Their reasoning: Water that recycles through a fountain wouldn’t heat up as pools do, because pools are fully exposed to the sun.

They were right, they said.

“It’s cool,” assured DeCarlo, sitting in her swimsuit.

As the children played in the spraying water, the moms let other parents know that it was fine for adults to take a dip.

“You can do that?” one woman asked.

In Fairfax, organizers of the Asian Festival said hot weather was not going to hinder their weekend-long event, held at George Mason University, which features sports, music and food from India, Thailand, China and the Philippines. It draws thousands.

“We’re Asian people, remember? We’re used to hot. But we also know not to overdo things and take breaks,” said Bing Branigin, an event spokeswoman. “We’re still going to eat spicy food.”

Staff writers Lori Aratani, Justin Jouvenal, Susan Kinzie, Michael Laris and Donna St. George contributed to this report.