These were the ingredients for tragedy in Texas, a state that is well acquainted with weather extremes of all kinds: high heat and deep cold, deluges and droughts, tornadoes and hurricanes, hail and snow. Indeed, the Hill Country, the part of the state where the Guadalupe River swelled on Friday, is sometimes called “flash flood alley” for how at risk it is to seemingly out-of-nowhere surges of water.

Humid air blows into the area from two main sources, the Gulf of Mexico and the tropical Pacific Ocean. When this air collides with cool air drifting down across the Great Plains, severe storms can erupt. The hilly terrain and steep canyons quickly funnel the rain into river valleys, transforming lazy streams into roaring cascades.

In parts of Texas that were flooded on Friday, the quantities of rain that poured down in a six-hour stretch were so great that they had less than a tenth of 1 percent chance of falling there in any given year, according to data analyzed by Russ Schumacher, a professor of atmospheric science at Colorado State University.

The Guadalupe River rose from three feet to 34 feet in about 90 minutes, according to data from a river gauge near the town of Comfort, Texas. The volume of water exploded from 95 cubic feet per second to 166,000 cubic feet per second.

And the warming climate is creating the conditions in Texas for more of these sharp, deadly deluges.

In the eastern part of the state, the number of days per year with at least two inches of rain or snow has increased by 20 percent since 1900, according to the most recent National Climate Assessment, the federal government’s flagship report on how global warming is affecting the United States. Across Texas, the intensity of extreme rain could increase another 10 percent by 2036, according to a report last year by John Nielsen-Gammon, the Texas state climatologist.

To understand patterns of heavy rain at a more local level, communities and officials rely on data from the National Oceanic and Atmospheric Administration. The agency has for decades published nationwide estimates of the probabilities of various precipitation events — that is, a certain number of inches falling in a particular location over a given amount of time, from five minutes to 24 hours to 60 days.

Engineers use NOAA’s estimates to design storm drains and culverts. City planners use them to guide development and regulations in flood-prone areas.

NOAA’s next updates to the estimates are scheduled to be released starting next year. For the first time, they are expected to include projections of how extreme precipitation will evolve as the climate changes, in order to help officials plan further ahead.

But in recent months, the Trump administration has cut staff at the agency and at the National Weather Service, which sits within NOAA. The administration has also dismissed the hundreds of experts who had been compiling the next edition of the National Climate Assessment, which was scheduled to come out in 2028. And it is proposing deep cuts to NOAA’s 2026 budget, including eliminating the office of Oceanic and Atmospheric Research, which conducts and coordinates climate research.

“It will be extremely dangerous,” said Constantine Pashos, a meteorologist at the Weather Service’s Austin/San Antonio office.

The service said it was difficult to pinpoint exactly where the rainfall would be heaviest on Saturday, but said the highest chance for it was east of San Antonio and Austin. The worst flooding on Friday was west of those cities, and the area could get another 2 to 4 inches of rain on Saturday.

A flash flood emergency was in place for much of Burnet County and western parts of Williamson and Travis Counties. The Weather Service warned people in those areas to seek higher ground immediately, calling it a “life-threatening situation.”

A flood watch was in effect for much of the region until 7 p.m., and it could be extended into Sunday if conditions do not improve.

The storm system that produced the flooding on Friday, killing at least 24 people, was worsened in part by Tropical Storm Barry, which caused significant flooding in southeastern Mexico, Mr. Pashos said. The storm led to a surge of tropical moisture in Central Texas.

The storms in the area are also slow moving or are drenching some areas more than once, Mr. Pashos said. He said residents should make sure they have a way to receive flash flood warnings, and warned that excessive runoff could produce flash floods in low-lying areas and along rivers and creeks.

The heavy rains could continue into Sunday, Mr. Pashos said, and the storm may linger in the region into Monday.

Here’s what they say:

For people searching for loved ones

Several reunification centers have been set up for people to connect with their missing loved ones, including:

• Arcadia Live Center in Kerrville, Texas

• Ingram Elementary School in Ingram, Texas

The Red Cross is also assisting with reunification efforts.

For those who want officials to conduct welfare checks, the authorities asked that they call the Kerr County Sheriff’s Office dispatch or the Kerrville Police Department.

For those seeking shelter

People whose homes were swept away or who have otherwise been displaced can find some assistance in these places.

In Kerrville:

• Calvary Temple Church

• Notre Dame Catholic Church

• Schreiner University Event Center

• First United Methodist Church

In Comfort, Texas:

• Comfort High School

• The Immanuel Lutheran Church

• The Lobby Coffee Shop

Other residents

For all residents in affected areas, officials are asking them to stay away from flood zones and downed power lines. Residents should also shelter in place and clear the way for emergency medical workers, the authorities said. Emergency workers in Kerr County have been hindered at some rescue sites by people filming and taking photos of the flood, as well as heavy traffic, they said.

“This incident is not over, and now is not the time to go look at the river,” the Kerrville Police Department said in a Facebook post, referring to the Guadalupe River. “Please help us by steering clear and giving us room to work.”

Parents of campers who have not been accounted for have been notified, the email said. About 750 girls were at the camp this week, Lt. Gov. Dan Patrick of Texas said at a news conference on Friday.

The camp said that it was assisting with search-and-rescue operations, but that it did not have power, water or Wi-Fi and was struggling to get more help because a nearby highway had washed away.

On social media and in text messages, parents circulated photos of some of the missing girls, and exchanged hopeful stories that they were hearing about dramatic rescues: girls clinging to trees, or floating downriver to a boys camp five miles away.

Camp Mystic aims “to provide young girls with a wholesome Christian atmosphere in which they can develop outstanding personal qualities and self-esteem,” its website said. It draws from families around Texas and beyond, with the youngest campers entering third grade in the fall.

The camp was established in 1926, according to its website, and has been run by generations of the same family since the 1930s. The current owners, Dick and Tweety Eastland, have been with the camp since 1974. They worked alongside the previous owners for years after graduating from the University of Texas in Austin. Camp activities include archery, cooking, cheerleading, fishing and a variety of sports. Videos posted to the camp’s Instagram account show large groups of girls participating in group dance performances this summer.

The affected stretch of the Guadalupe River is home to several summer camps for children, including Camp La Junta for boys, about five miles from Camp Mystic. The boys camp informed families on Friday that all campers there were safe and fed, but evacuations would not begin until at least 7 p.m. local time on Friday.

The Facebook page for another nearby girls camp, Heart o’ the Hills, reported that it was not in session when the flooding took place.

Ten of the teenagers were swept away and killed; 33 others, and four adults, were rescued. Some of the survivors held on to the upper branches of cypress and pecan trees, praying until helicopters arrived to carry them to safety, The New York Times reported. At the time it was the worst flooding of the Guadalupe River in 55 years, The Times reported.

Rob Kelly, the Kerr County judge, said at a news conference on Friday morning that the flooding this time might exceed what took place in 1987, based on the waterline at his property along the river.

As in Friday’s flooding, in 1987, five to 10 inches of rain fell in the upper headwaters of the Guadalupe River basin. In Hunt, Texas, where the Guadalupe River forks, over seven inches had fallen since Thursday afternoon, which was the highest total at the site since the early 1990s.

The rapid rainfall led to a fast rise of the river that accelerated to over 29 feet before sunrise on Friday, the second highest crest ever recorded. Still, it might have even gone higher. As the waters rose 20 feet in two hours, they flooded the instrument box that the U.S. Geological Survey uses to send river gauge data.

The box stopped transmitting at 4:35 a.m. local time on Friday.

In 1987, though, warnings were issued early in the morning to summer camps along the river, and it was unclear why the church vehicles crossed the swollen river. All but one body was recovered.

More than a year later, a sheriff’s deputy in Kendall County, Texas, said of the missing camper that a cresting river would create sandbars, and a body could end up buried, possibly until another big flood comes to “turn things upside down again.”