As people waded in chest-high floodwaters, Houston turned its main convention center into a shelter Sunday, evoking memories of Hurricane Katrina, when breached levees in New Orleans stranded tens of thousands of people in squalid conditions at that city's football stadium and convention center.
Elected officials have vowed to heed the lessons from Katrina in 2005, when about 30,000 evacuees spent days packed inside the sweltering Superdome with limited power and water and a roof that was shredded in the howling wind.
The fiasco exposed the failure of both the city and federal government to prepare adequately for the storm.
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Sen. Chuck Grassley of Iowa told President Donald Trump on Twitter to "keep on top of hurricane Harvey" and not repeat the mistakes that President George W. Bush made with Katrina. Bush was heavily criticized for a slow federal government response to the storm, which left more than 1,800 people dead and caused $151 billion dollars in damage.
"Got your message loud and clear. We have fantastic people on the ground, got there long before #Harvey. So far, so good!" Trump tweeted back.
Later, the White House announced Trump would go to Texas on Tuesday.
There is no doubt the challenge will be huge for Houston, a city of 2.3 million residents.
Forecasters predict the remnants of Harvey could dump as much as 50 inches (127 centimeters) of rain in parts. "The breadth and intensity of this rainfall is beyond anything experienced before and is resulting in catastrophic flooding," the National Weather Service said in a statement.
Harvey made landfall Friday as a Category 4 hurricane. It has since been downgraded to a tropical storm.
In New Orleans, almost 80 percent of residents were evacuated days ahead of Katrina's arrival. In contrast, Houston Mayor Sylvester Turner advised people to stay in their homes, saying it was not feasible to completely evacuate the nation's fourth-largest city.
Houston authorities urged people to escape to the roofs of their homes to avoid becoming trapped in attics, which caused more than a dozen deaths in Katrina's aftermath.
Rescue workers were so overwhelmed with calls for help Sunday that they initially were responding only to life-or-death situations.
The number of shelters was expected to increase dramatically.
Dallas also opened its convention center to shelter 5,000 people from the southern part of the state.
In Houston, the George R. Brown Convention Center received hundreds of people as authorities scrambled to ready the building with 1.8 million square feet (0.17 million sq. meters) of space. Officials asked for help from restaurants to feed the growing population.
In 2005, Houston hosted Katrina survivors, with the convention center and the Astrodome receiving thousands of people fleeing the horrific conditions of New Orleans' shelters.
Among them was Raeann Barber, who came to Houston with nothing but the nightgown on her back.
The 37-year-old woman, who rebuilt her life in Houston, found herself again fleeing her home when she woke up to knee-high water in her apartment. A Coast Guard boat helped her escape.
"One way or another, guess what?" she said as she looked for a cot at the convention center. "To me, the Lord will make the way, one way or another."
The Texas city won applause for its efforts in helping Katrina survivors. But some people Sunday were questioning city officials' decisions so far in this storm.
Desiree Mallard, who escaped her apartment complex by using an inflated air mattress to float her nearly 2-year-old son through chest-high floodwaters, said she wished she had left before Hurricane Harvey approached the Texas Gulf Coast. But she saw on the news to stay in place.
"And then when it got bad, they said it's too late to evacuate," she said.
Asked if this storm could become Houston's Hurricane Katrina, Texas Gov. Greg Abbott, who had contradicted the mayor's advice and urged people to flee from Harvey's path, ducked the question.
"As far as the evacuations, now is not the time to second-guess the decisions that were made," Abbott told reporters in Austin. "What's important is that everybody work together to ensure that we are going to, first, save lives and, second, help people across the state rebuild. And because of the effort that we've been able to put together, I think and believe we will be very successful."
Associated Press writers Nomaan Merchant and Will Weissert contributed to this report.