World Swelters in Record-Breaking Heat

“It just feels awful,” said Mazey Christensen, 20, a scooper at Sweet Republic, an ice cream shop in Phoenix.

Business at the store has been steady; on blistering days, customers tend to go for fruity flavors like watermelon sorbet and pineapple whip. But they mostly visit the shop later in the day when the sun is not so scorching.

The temperatures are “very extreme,” said Matt Salerno, a meteorologist with the National Weather Service in Phoenix. “We’re talking 10 degrees above where they normally are.” The city set another heat record on Monday: eight consecutive days in which the overnight temperature never dipped below 90 degrees.

The heat is particularly brutal and inescapable at the sprawling homeless encampment in central Phoenix known as “The Zone.” Phoenix is slowly clearing tents block by block, but healthcare workers in the Zone say that regular counts show the number of people living there has remained the same or even grown.

There are barely any trees and, this July, people have been suffering second-degree burns after they pass out or fall asleep on the hot asphalt and sidewalks.

There are few sources of running water other than donated bottles and portable wash stations. So a spigot outside a shelter often has a line of people pouring water over their heads and filling up five-gallons jugs to take back to their tents.

“It just sucks it right out of you,” said Charles Outen, 49, who said he had spent the summer hopscotching between cooling centers during the day and sleeping at local churches at night to avoid the heat.

For many in the city and across the Southwest, the searing temperatures have come with little relief: The monsoon season — which typically brings cooling thunderstorms to the deserts of Arizona and New Mexico — is arriving later than usual.

And all across the South, the heat has been not only strikingly severe, but also abnormally persistent.

This week, hot and humid conditions were expected to worsen along the Gulf Coast and throughout the Southeast, according to the Weather Service. Across the country, about 100 million people are under heat alerts. And even parts of Northern states, including Michigan, New York and Vermont, have recently broken daily temperature records.

In Palm Springs, Calif., a desert resort city in Southern California, residents and tourists have been trying their best to keep cool in temperatures that spiked to around 115 degrees.

Zach Stone, who lives in his car, says the heat inside the vehicle is unbearable. To find relief, he came to the Demuth Community Center, where he worked on a puzzle in the gym.

“They have bread and water and there’s vending machines and bathrooms, and that’s a huge convenience,” he said.

The heat can be especially brutal for those who were already dealing with medical conditions like cancer, diabetes, drug addiction and heart disease, said Dr. Jerald Moser, a co-director of the emergency department at the Tucson Medical Center in Tucson, Ariz., where the heat wave has brought in more patients than usual. Temperatures are forecast to exceed 110 degrees there this week.

People without shelter or access to water are especially at risk, Dr. Moser said, adding that many of them wind up in emergency rooms after being found incapacitated on the ground, sometimes with secondary burns from the scorching sidewalks.

“We see people passing out from full-blown heat stroke with a core body temperature of 104 degrees,” he said.

The persistent heat in the Southwest is the result of a high-pressure system that has been parked over the region for weeks. It has been particularly stubborn this year, delaying cooling storms.

The monsoon schedule varies from one year to the next, said Michael Crimmins, an environmental science professor at the University of Arizona in Tucson, so while it is not yet clear whether climate change is to blame for the heat wave’s persistence, it has very likely made the daily high temperatures even higher.

In the Phoenix area, there have been 12 reported heat-related deaths this year through mid-June, and 40 more open cases where heat is being investigated as a factor, according to the medical examiner in Maricopa County, which includes Phoenix.

In Texas, the heat this year has prompted cotton plants, especially in the southern parts of the state, to bloom early. “It’s running ahead of time, which is not good,” said Josh McGinty, an agronomist with the Texas A&M AgriLife Extension Service whose office in Corpus Christi is bordered by cotton fields.

Normally during this time of year, a few bulbs would be starting to unfurl. Instead, Mr. McGinty said, “every fruit on the plant is open, and they shouldn’t be. The heat is just shutting the plants down. They’re in survival mode at this point.” But even that, he said, is better than last year, when the cotton crop suffered even more because of droughts.

Farther east, residents of Southern states are bracing for a long spell of hot and muggy days. Heat indexes, which measure how hot it feels outside while accounting for both temperature and humidity, were expected to surpass 100 degrees this week in many cities including Jackson, Miss., Montgomery, Ala., and Tallahassee, Fla.

On Monday afternoon, Ralph Horton was driving east along Interstate 20 to his home Tallapoosa, Ga., when he stopped in Vicksburg, Miss., for a break.

He was traveling from Texas, where he had spent a few days. “Oh my gosh, it was hot,” he said.

On Monday, he stood on an overlook with a view of the Mississippi River, anticipating a different kind of heat — the kind that is oppressive even when the temperatures don’t reach triple digits. “The humidity is killer in this part of the country,” Mr. Horton said.

The spot where he stood was already under a heat advisory, with heat indexes forecast to reach around 110 degrees on Tuesday.

Reporting was contributed by Maggie Miles, Jack Healy and Sheryl Kornman.