San Francisco's recent heat wave is now San Francisco's deadly heat wave, officials said Wednesday, tracing the demise of three residents to the city's record-breaking temperatures. Add to that a release Thursday from the San Mateo County Coroner saying that three more people died there as a result of the heat — and the death toll may rise as more reports come in from other counties.

The San Francisco Medical Examiner's Office announced that three elderly people died due to “probable” heat-related causes this weekend, the Ex reports.

All three were born in the 1920s or 1930s, lived alone, and died at home, the ME's office says.

None of the deaths were preceded by calls to 911, putting to rest worries that any of the dead were among the 28 life-threatening calls made over a weekend so short on EMTs that fire engine crews had to wait 20 minutes or more for an ambulance to arrive.

San Mateo County Coroner Robert Foucrault told the Chronicle that we can add to that list Patrick Henry of Pacifica, 90; Ernesto Demesa of Daly City, 79; and Loraine Christiansen of Millbrae, 95. Demesa and Henry both lived in homes without air conditioning, Demesa alone and Henry with his wife. Christiansen lived in an assisted living facility.

As noted by NBC Bay Area, "People of advanced ages living independently are the most vulnerable in extreme conditions," saying that the ME's office recommends "well checks and frequent contact to ensure friends, family, and neighbors are healthy and not in need of assistance."

When contacted by the Chron regarding the deaths, Department of Public Health spokeswoman Rachael Kagan said “We will look deeply into these incidents and see what we can learn about improving outreach to elderly and vulnerable populations."

On Tuesday, Supervisors London Breed, Aaron Peskin and Jane Kim called for a hearing on the city's preparation for the heat wave, which the Chron described as "sluggish."

“It is deeply concerning that in a city with San Francisco’s resources, at least three preventable deaths happened as a result of the heat wave — and many more people were affected in non-fatal ways,” Peskin says.

“We will be asking the tough questions to make sure San Francisco is not caught flat-footed again."

And well he should: As previously reported, climate scientists are suggesting that the recent heat wave could be the first of many, as continued climate change makes for conditions leading to extreme temperatures like last weekend's.

"It makes more sense to ask whether global warming made an event more likely," UCLA climate scientist Dr. Daniel Swain says. "And in the case of an unprecedented extreme heat wave, the answer these days is usually yes."

Related: Record-Breaking Heat Could Be Ongoing Trend For SF Bay Area
ABC 7 Weatherman Drew Tuma Collapsed From Heat Exhaustion During Heatwave

*This post has been updated throughout.