As the temperature soared in the Houston-area home Janet Jarrett shared with her sister after losing electricity in Hurricane Beryl, she did everything she could to keep her 64-year-old sibling cool. But on their fourth day without power, she awoke to hear Pamela Jarrett, who used a wheelchair and relied on a feeding tube, gasping for breath. Paramedics couldn’t save her, and the medical examiner has determined that her death was caused by the heat. “It’s so hard to know that she’s gone right now because this wasn’t supposed to happen to her,” says Janet Jarrett.

Almost two weeks after Beryl hit, heat-related deaths during the prolonged power outages have pushed the number of storm-related fatalities to at least 23 in Texas, per the AP. While it may be weeks or even years before the full human toll of the storm in Texas is known, understanding that number helps plan for the future. What is known so far:

• Just after the storm hit, the deaths included people killed by falling trees and people who drowned when their vehicles became submerged in floodwaters. In the days after the storm passed, deaths included people who fell while cutting limbs on damaged trees and heat-related deaths.
• But half of the deaths attributed to the storm in Harris County, where Houston is located, are heat related, according to the Harris County Institute of Forensic Sciences.
• Officials are still working to determine if some deaths that have already occurred should be considered storm related. But even when those numbers come in, getting a clear picture of the storm’s toll could take much more time. With power outages and cleanup efforts still ongoing, the death toll likely will continue to climb.
• Experts say that while a count of storm-related fatalities compiled from death certificates is useful, an analysis of excess deaths that occurred during and after the storm can give a more complete picture of the toll. For that, researchers will compare the number of people who died in that period to how many would have been expected to die under normal conditions.

(More Hurricane Beryl stories.)