Separately, in the Pacific, Hurricane Fausto is projected to weaken as it passes north of the Hawaiian Islands as a tropical storm on Tuesday and Wednesday, while Hurricane Genevieve is strengthening off the coast of Mexico’s Baja California.

Extreme heat warnings and advisories stretch across the central US from the North Dakota–Canada border southward to Dallas. At least 20 daily high-temperature records are expected to be challenged or broken across the region on Sunday, with 33 warm overnight lows also under threat, according to the US Weather Prediction Center. The combination of heat and humidity will make conditions feel as scorching as 112°F (44°C) as the heat index climbs across broad swaths of the central US, the National Weather Service said. In St. Louis, where Sunday’s high is forecast to reach 97°F, atmospheric moisture could push the feels-like temperature closer to 116°F; Dallas is expected to see a high of 102°F, with a heat index as high as 109°F.

“A big heat dome is centered over the Rocky Mountains and Plains that’s going to bring record-breaking temperatures,” said Alex DaSilva, a meteorologist with commercial forecaster AccuWeather Inc. “Triple-digit heat is stretching from the Rockies to the Plains. There’s some dangerous heat there.”

At least 105 million people across the US are under heat advisories or extreme heat warnings for Sunday, including in Southern California, the Weather Prediction Center said. As the weather drives people to air conditioners for relief, the Southwest Power Pool and the Midcontinent Independent System Operator — which together cover at least parts of 20 states — have indicated that power loads may rise. Stagnant air trapped beneath the large high-pressure system may also reduce wind-generated power during peak demand periods. While high temperatures can damage some crops, they tend to benefit big retailers as sales of air conditioners and fans surge.

On top of the sweltering heat, there is a chance for severe thunderstorms, wind, and hail at the system’s edges, DaSilva said. Saturday brought 89 filtered reports of high winds and two of large hailstorms, mainly in Montana and South Dakota, the US Storm Prediction Center reported. There is a level-two risk of dangerous wind and thunderstorms across the upper Midwest again for Sunday, focused mainly on Minnesota and Wisconsin, the agency said.

“Any time you get these areas of high pressure, you have to watch the periphery as well,” DaSilva said. “There will be multiple chances to see severe weather.”

The heat dome will continue to drive temperatures higher across the western and central US this week before the focus shifts to the west by next weekend, said Bob Oravec, a senior branch forecaster at the Weather Prediction Center. Heat across the Southwest and California is likely to persist into the beginning of August, he added.

In the Pacific, the main impact from Fausto is likely to be rough surf and rip currents on the northern-facing shores of the Hawaiian islands, said AccuWeather’s DaSilva. “Overall, I don’t think this will be a big deal for them.” As Fausto weakens, Hurricane Genevieve is intensifying off Mexico’s southwest coast, potentially on its way to becoming a Category 4 major storm, bringing rough seas to the southern parts of the Baja California peninsula.