But the professional first responders could not handle all of the thousands of calls from people endangered by rising waters. The roads were largely impassable. Residents reported calling 911 and getting no answer. The Red Cross command center in Houston became physically isolated amid floodwaters.
So people had to take matters into their own hands. They connected on social media, asking for or offering help. They launched private boats and kayaks. They carried people to higher ground.
"You're seeing rescues from very expensive, high-end to very low-rent apartments," said West Houston business owner Jody Goldstein, 51. "It's hitting people equally."
The disaster Hurricane Harvey — now a tropical storm — has created is immense in scale, encompassing thousands of square miles of Southeast Texas. It has brought epic flooding that will affect millions of people. Rivers are still rising, the rain still falling.
"This will be a devastating disaster, probably the worst disaster the state's seen," William "Brock" Long, administrator of the Federal Emergency Management Agency, told The Washington Post on Sunday. "The recovery to this event is going to last many years to be able to help Texas and the people impacted by this event achieve a new normal."
In an interview a few weeks ago, Long shared the one thing that worried him most when it comes to natural disasters: "You know what's keeping me up at night? This country has not been hit by a major hurricane since 2005."
That was the right thing to worry about, it has turned out. Long, just two months on the job, is coordinating the federal response to Harvey — the first storm of Category 3 or higher to hit the United States in 12 years — and the system's lethal aftermath.
FEMA acts as the nerve center for the entire federal government response, which now includes 5,000 federal employees in Texas, officials supplied by the Coast Guard, the Energy Department (whose staffers look for power failures and effects on oil production), the Department of Health and Human Services, and many other federal agencies.
FEMA said Sunday afternoon that it had 400 urban search-and-rescue personnel in Southeast Texas and that more than 500 additional rescuers would arrive Sunday evening. As of noon Sunday, the Coast Guard had 423 active-duty and auxiliary personnel and reservists deployed to the disaster zone, along with 16 helicopters flying rescue missions, Coast Guard spokesman Dave French said. The number of helicopters is slated to increase to 24 by Monday morning.
French said the agency has launched more than 2,000 rescue efforts and is searching for people stranded in homes and on rooftops in the Houston area.
The Department of Health and Human Services has assembled a team of 650 medical professionals in Dallas, waiting for orders to deploy to communities hit by the storm. Employees flew to the area Wednesday, Thursday and Friday from California, Ohio and other states. "We can open a small emergency room," said Edward Gabriel, HHS's principal deputy assistant secretary for preparedness and response.
President Trump signed a federal disaster declaration for the state, and Long said the move freed him to unify efforts and send in federal resources. Trump's declaration made federal financial assistance available to victims of the storm; they will have to apply for federal aid and can find information at disasterassistance.gov .
The unfolding disaster reflects the special vulnerability of Houston, the nation's fourth-largest city, which is barely above sea level, sits next to the stormy Gulf of Mexico, and has grown into a sprawling, heavily paved metropolis notorious for flooding.
Harvey's winds are creating a storm surge along the coast and in the bays and estuaries, essentially jacking up "sea level" and reducing drainage; gravity isn't much help.
The flooding in Houston also is slowing relief efforts elsewhere in Texas, which has experienced widespread flooding. Hundreds of Red Cross staffers and volunteers flew to Houston, expecting to drive to other affected areas to the south. But as the weather deteriorated Saturday, the organization determined that it was not safe to divert its staffers, issuing a "shelter in place" order.
Across Texas, 35 Red Cross shelters are open, but officials say the number will increase greatly on Monday. Relief efforts also are being slowed by a lack of hotel rooms in Corpus Christi, where many businesses remain closed because of widespread power outages. Those that remain open are overwhelmed by an influx of utility workers, fire and police crews, journalists, and evacuees.
Although FEMA has jumped on the Texas storm, its director has emphasized in recent interviews with The Post that the initial response to a disaster — whether it's a wildfire, a flood, a tornado or some other calamity — has to come from local and state agencies.
"Emergency management's a partnership. It's all based on a community's capacity to handle an event," Long said. "All disasters begin and end at the local level." As Long has described it, FEMA's job is to arrive when the local and state agencies are overwhelmed, which is what is happening in Texas.
Long has spoken of the need for a massive overhaul in how the country prepares for disasters, noting that the federal government alone can't always save the day. Ordinary citizens need to be prepared to be first responders, Long said. They need to have personal emergency plans. They need to be able to feed themselves for several days if disaster strikes. They need to be ready to save neighbors in harm's way.
"People need to be the help before the help arrives," he said this month at FEMA headquarters on what the agency referred to as a "blue-sky day" — a day without a major national catastrophe.
"I think we have to look at how we ask citizens to be ready, first of all. We used to look at citizens as disaster victims. Now they're looked at as what we call disaster survivors," he said. "I think we have to focus our attention back on the citizens and how we're training citizens to be truly ready for a disaster. Whether it's an active shooter, whether it's a tornado, in many cases citizens find themselves having to render first aid, CPR, or making safety decisions before the true first responders arrive."
W. Craig Fugate, President Barack Obama's FEMA director for two terms, said this month that Long's words about shared responsibility among federal, state and local agencies are an echo of what Fugate advocated for when he ran the agency.
Both men said, in different language, something similar: Americans tend to get complacent about the possibility of a disaster. "We have a long way to go," Long said about the nation's overall disaster readiness. Fugate, now retired, was more blunt: "It sucks."
Harvey made landfall late Friday as a Category 4 hurricane, then crept slowly inland. On Sunday, it was still a tropical storm, with a center of circulation 35 miles west-northwest of Victoria, Tex. The system had started to backtrack slightly Sunday, moving at just 2 mph to the southeast.
Harvey is the first major hurricane — Category 3 or higher — to hit the United States since Wilma in 2005.
Earlier that year, Hurricane Katrina killed more than 1,800 people, most of them in Louisiana, and put much of New Orleans underwater. FEMA's initially sluggish and ineffective response to Katrina tarnished the agency's reputation. It became a late-night talk show joke after President George W. Bush praised Michael Brown, his FEMA director: "Brownie, you're doing a heck of a job."
A 2006 law that Congress passed after Katrina is credited with improving the culture of an agency that had suffered from budget cuts and a lack of professional emergency managers early in the Bush presidency. The law required FEMA to dispatch teams to the scene along with massive relief supplies before a disaster hit.
Under Fugate, the agency improved coordination with the Red Cross and state and local emergency managers, and it boosted its use of social media to offer assistance to storm victims.
Yet even as nearly 60 federal agencies from the Defense Department to the Internal Revenue Service were on hand for the response to and recovery from Hurricane Sandy in 2012, FEMA confronted the limitations of bureaucracy in any disaster.
Large areas of New York and New Jersey were without electricity for weeks, for example, as FEMA struggled to get private utility companies and state agencies to move faster to restore power. Many homeowners who applied for disaster assistance found only confusion as they tried to navigate the many federal agencies tasked with helping them.
Trump has proposed cuts to federal emergency response funding. FEMA's $3.5 billion budget would lose $361 million under the spending plan the White House submitted to Congress in March.
Some programs criticized for a lack of effectiveness would be cut, but so would the federal commitment to helping state and local governments prepare for natural disasters through training, coordination, state-of-the-art equipment, and salaries and benefits for staff.
The Coast Guard's $9.1 billion budget for the fiscal year that starts Oct. 1 would be cut, too, by 14 percent.
With the Harvey disaster unfolding, the question is whether the storm could become another Katrina.
"It's hard to say. This is totally different from Katrina," Long said Sunday, recounting Harvey's unusual weather pattern. "This is an incredibly unique event."
Tim Craig in Corpus Christi contributed to this report.