Record daily high temperatures in Oregon were suspected in four deaths reported in the Portland area Monday as much of the country continued to swelter under an early heat wave.

California, Nevada, Arizona, Oregon, Washington and Idaho on Monday were under an excessive heat warning, the National Weather Service’s highest alert, while parts of the East Coast as well as Alabama and Mississippi were under heat advisories. The death of a motorcyclist Saturday in California’s Death Valley also was blamed on the severe heat.

In Oregon’s Multnomah County, home to Portland, the medical examiner is investigating four suspected heat-related deaths recorded on Friday, Saturday and Sunday, officials said. Three of the deaths involved county residents who were 64, 75 and 84 years old, county officials said in an email. Heat also was suspected in the death of a 33-year-old man transported to a Portland hospital from outside the county.

Authorities said it could take months to confirm the causes of death.

Portland broke daily record temperatures on Friday, Saturday and Sunday and was on track to do so again on Monday with a forecast high of 102 degrees Fahrenheit (38.9 Celsius), National Weather Service meteorologist Hannah Chandler-Cooley said.

“We are looking at the potential for breaking more records,” she said.

The county has been operating three daytime cooling centers since Friday to help people who are vulnerable to heat-related illness, such as those living outside, older people, people with disabilities and people whose homes don’t have air conditioning.

High temperatures were expected in Portland through Tuesday evening, the National Weather Service said, with the most dangerous portion of the multi-day heat wave starting on Monday.

The temperatures aren’t expected to peak as high as they did during a similar heat wave in 2021 — which killed an estimated 600 people across Oregon, Washington and western Canada — but the duration could pose a problem. Many homes in the region lack air conditioning, and round-the-clock hot weather means people’s bodies aren’t able to sufficiently cool down at night. The issue is compounded in many city settings, where concrete and pavement can store the heat, essentially acting as an oven.

The U.S. heat wave came as the global temperature in June was record warm for the 13th straight month and it marked the 12th straight month that the world was 1.5 degrees Celsius (2.7 degrees Fahrenheit) warmer than pre-industrial times, the European climate service Copernicus said.

Dozens of locations in the West and Pacific Northwest tied or broke previous heat records over the weekend.

A high temperature of 128 F (53.3 C) was recorded Saturday and Sunday at Death Valley National Park in eastern California, where a visitor died Saturday from heat exposure and another person was hospitalized, officials said.

The two visitors were part of a group of six motorcyclists riding through the Badwater Basin area amid scorching weather, the park said in a statement.

The person who died was not identified. The other motorcyclist was transported to a Las Vegas hospital for “severe heat illness,” the statement said. Due to the high temperatures, emergency medical helicopters were unable to respond, as the aircraft cannot generally fly safely over 120 F (48.8 C), officials said.

The other four members of the party were treated at the scene.

“While this is a very exciting time to experience potential world record setting temperatures in Death Valley, we encourage visitors to choose their activities carefully, avoiding prolonged periods of time outside of an air-conditioned vehicle or building when temperatures are this high,” park Superintendent Mike Reynolds said.

Caution is urged during hot weather

Officials warned that heat illness and injury are cumulative and can build over the course of a day or days.

Across the desert in Nevada, Las Vegas on Sunday set a record high of 120 F (48.8 C).

Triple-digit temperatures were common across Oregon, where several records were toppled, including in Salem, where on Sunday it hit 103 F (39.4 C), topping the 99 F (37.2 C) mark set in 1960.

“Drink plenty of fluids, stay in an air-conditioned room, stay out of the sun, and check up on relatives and neighbors,” read a weather service advisory for the Baltimore area. “Young children and pets should never be left unattended in vehicles under any circumstances.”

Heat records shattered across the Southwest

Rare heat advisories were extended even into higher elevations including around Lake Tahoe, on the border of California and Nevada, with the weather service in Reno, Nevada, warning of “major heat risk impacts, even in the mountains.”

“How hot are we talking? Well, high temperatures across (western Nevada and northeastern California) won’t get below 100 degrees (37.8 C) until next weekend,” the service posted online. “And unfortunately, there won’t be much relief overnight either.”

More extreme highs are in the near forecast, including possibly 130 F (54.4 C) around midweek at Furnace Creek, California, in Death Valley. The hottest temperature ever officially recorded on Earth was 134 F (56.67 C) in July 1913 in Death Valley, though some experts dispute that measurement and say the real record was 130 F (54.4 C), recorded there in July 2021.

___

Weber reported from Los Angeles. AP journalists Margery Beck in Omaha, Nebraska, and Walter Berry in Phoenix contributed to this report.