It said it expects to restore power to another 750,000 customers by the end of the weekend — leaving nearly 400,000 customers for whom power is unlikely to be restored within a week of Beryl’s landfall early Monday.

At least nine people have died in Texas and Louisiana after the storms — people who were killed by falling trees, who drowned after being trapped in vehicles in rising floodwaters, or who were left vulnerable during power outages. Now, there are concerns the outages could cause more casualties as heat indexes surge into the triple digits.

Though cooling centers have opened across the region and the local bus authority will transport people to them for free, Brian Murray, deputy emergency management coordinator for Harris County, said he worries there are some people out there stuck at home without power.

“We know there are residents in that situation; we just don’t know who they are or where they are,” he said. So far, the county had not received any reports of heat-related fatalities, he said. “We’re hoping we don’t.”

The slow pace of power grid recovery underscores how, despite being a relatively low-end hurricane, Beryl unleashed major damage on a landscape that was already saturated and trees already weakened by other recent storms. Along the coast, parts of the electric system will need to be rebuilt entirely, and damage was also significant in dense parts of Houston, CenterPoint officials said.

Entergy, which serves customers in parts of eastern Texas, was meanwhile reporting 102,000 outages at midday Thursday, mostly in Montgomery County just north of Houston. The utility said that it expected to restore all but about 15,000 of those by Friday evening but that for some areas, power might not turn back on until Saturday or Sunday.

About 1.3 million utility customers were without power across all of Texas as of midday Thursday, according to PowerOutage.us.

Outages were having major impacts across southeastern Texas, where 160 boil water notices were in effect across eight counties and 135 wastewater treatment plants were offline, according to Nim Kidd, chief of the Texas Department of Emergency Management. A dozen hospitals were under internal disasters, he said; the designation that means routine hospital operations are compromised.

The Houston region was meanwhile under a heat advisory Thursday, with high temperatures forecast in the lower to mid-90s and humidity making it feel as much as 10 degrees hotter. Temperatures are forecast to approach the mid-90s each day for the next week, at least.

“This heat is especially dangerous if you remain without power and doing strenuous outdoor work,” the National Weather Service’s Houston forecast office warned. “Please stay hydrated and use safe generator practices.”

Harris County officials sent a wireless alert to residents Thursday urging them to be careful using portable generators after reports from fire stations about an uptick in calls related to possible carbon monoxide poisoning, Murray said. The hope, he said, is that utility crews restore outages sooner than later.

Gov. Greg Abbott (R), who is traveling in Asia on an economic development trip and left Lt. Gov. Dan Patrick in charge, on Wednesday called for an investigation into why the Houston region has repeatedly endured long-term, widespread power outages.

Frustration with CenterPoint was mounting during what was just the latest electricity crisis — in May, an intense storm known as a derecho also caused about 1 million power outages, some of which took six days to restore.

“It appeared they were maybe not as prepared as they should have been,” Patrick said at a Thursday news conference. “We’ll see what the facts are later.”

The utility said trees across the region “contributed heavily to the outages as they were vulnerable due to significant freezes, drought and heavy rain over the past three years.”

“We understand how difficult it is for our customers to be without power, particularly in this summer heat,” Lynnae Wilson, a CenterPoint senior vice president, said in a statement. “We know that our customers are counting on us, and we are committed to working as safely and quickly as we can until every last customer is back on.”