Authorities in Portland, Oregon, said they would keep cooling shelters open until Sunday night as a likely record-breaking heatwave brought scorching weather to the normally temperate region.
At least seven people are suspected to have died from hyperthermia since the hot spell began a week ago.
The most recent suspected heat-related death was announced by Clackamas County officials on Saturday, Portland television station KOIN-TV reported – an elderly man who died in his home, where he did not have working air conditioning.
The other six suspected hyperthermia deaths occurred earlier in the week in Multnomah, Umatilla and Marion counties.
Jessica Mokert-Shibley, a spokeswoman for Multnomah County, said the county, the city of Portland and other organisations would keep overnight cooling centres open until Sunday evening. Nearly 250 people used the overnight shelters on Friday night, she said.
Temperatures in Portland have neared triple digits all week, hitting a high of 102F (38.9C) on Tuesday.
The National Weather Service issued an excessive heat warning for both the Portland and Seattle, Washington, regions lasting until late Sunday evening, with temperatures expected to reach as high as 103F (39C).
Shawn Weagle, a NWS meteorologist based in Portland, said on Saturday that the region had likely tied its record for its longest heatwave with six consecutive days in a row topping 95F (35C). A new record could be set on Sunday, he added.
Temperatures have remained abnormally high at night — only dropping to about 70F (21C) — making it hard for residents to adequately cool off their homes before the sun rises, Mr Weagle said. Many homes in the region lack air conditioning.
“It’s an increasingly common issue with our heatwaves, the lack of recovery at night,” he said. “That really impacts people who don’t have air conditioning. It’s the ‘urban island effect’ — the downtown Portland core has been built up so much, and that concrete is slower to cool down overnight than a rural valley or even suburban neighbourhood would.”
The region’s heatwaves also seem to be getting stronger in general, Mr Weagle said.
He said expects relief from the hot weather will come midweek.
“Right now it’s looking like Tuesday we’ll start to get closer to normal but still in the 80s, and by Wednesday we should be a touch below normal temperatures,” he said.
The Seattle region was slightly cooler but still topped 90F (32C) on Saturday for a fifth straight day, compared with normal temperatures in the high 70s.
Mr Weagle said people should drink plenty of water, do what they can to stay cool and check on their neighbours, particularly older people and those who are at greater risk of heat-related illnesses.
Climate change is fuelling longer heatwaves in the Pacific Northwest, a region where week-long heat spells were historically rare, according to experts.
Residents and officials in the Northwest have been trying to adjust to the likely reality of longer, hotter heatwaves following last summer’s deadly “heat dome” weather phenomenon that prompted record temperatures and deaths.
About 800 people died in Oregon, Washington, and British Columbia during that heatwave, which hit in late June and early July.
Temperature at the time soared to an all-time high of 116F (46.7C) in Portland and broke heat records in cities and towns across the region. Many of those who died were older and lived alone.