Dangerous heat wave continues along West Coast

Millions of people on the West Coast are facing a continuation of intense early-season heat for multiple days, forecasts show.

Washington state began seeing record-breaking temperatures at the start of the weekend. On Sunday, Seattle could reach 90 degrees for the first time this year, which would also break the daily record high of 88 degrees. Highs in Portland and Medford, Oregon, could also break records before the weekend is through.

These temperatures are coming well in advance -- more than a month -- ahead of when they usually start creeping up.

The region, known for its typically cool and rainy climate, has been experiencing more uncharacteristic heat waves and wildfires in recent years.

The temperatures could raise the risk of heat-related illness, especially as the majority of households in the region are not equipped with central air conditioning.

High temperatures are cranking up even more further down the coast. Fresno, California, is forecast to be approaching 100 degrees on Sunday, with high temperatures of 95 degrees to 100 degrees for at least the next five days.

About 12 million people are under heat advisories along the West Coast.

More extreme heat is an indicator of human-caused climate change, according to scientists.

Extreme heat is the deadliest natural hazard in the U.S.

More than 230 locations in the U.S. have seen the annual number of minimum mortality temperature heat days -- temperatures at which the health risks also start to rise -- by 21 more days on average since 1970, according to an analysis by Climate Central.

While the South and Southeast tend to be the riskiest heat spots, increases in days above local minimum mortality temperature were observed in every region in the U.S., according to Climate Central.

ABC News' Tracy Wholf contributed to this report.