The extremely dangerous storm is predicted to bring days of rain to southeast Texas starting on Aug. 25. (NASA/YouTube)

The extremely dangerous storm is predicted to bring days of rain to southeast Texas starting on Aug. 25. (NASA/YouTube)

Texas is bracing for potentially catastrophic flooding and winds as Hurricane Harvey intensified Thursday and cruised toward a late Friday impact near Corpus Christi.

The National Hurricane Center described Harvey’s sudden strengthening as “astounding.” The storm is expected to strike as a Category 3 hurricane — meaning with winds greater than 111 miles per hour — making it the most powerful storm to make landfall in the United States since Hurricane Wilma in 2005.

Despite the increasingly alarming forecasts, officials in Corpus Christi held off on ordering mandatory evacuations of the city, which includes a great deal of low-lying land and a barrier island. “I’m not going to risk our police and fire people trying to drag somebody out of the house if they don’t want to go,” Mayor Joe McComb said Thursday.

But the warnings from the National Weather Service grew increasingly dire.

The NWS office in Corpus Christi said Friday that a combination of flooding from the storm surge and rainfall should make some locations “uninhabitable for an extended period.” It also warned of “structural damage to buildings, with many washing away” and that “streets and parking lots become rivers of raging water with underpasses submerged.”

Capital Weather Gang's Jason Samenow breaks down the three main threats from Harvey: Torrential downpours, a storm surge and heavy winds. (Claritza Jimenez,Jason Samenow/The Washington Post)

By early Friday, Harvey was about 140 miles southeast of Corpus Christi and moving toward shore at about 10 mph, the hurricane center said.

The surprise hurricane is poised to be the first major test of disaster response for the Trump administration, whose appointee to lead the Federal Emergency Management Agency — William B. “Brock” Long — was confirmed in June.

“With Harvey now strengthening at a faster rate than indicated in previous advisories, the intensity forecast has become quite concerning,” the National Hurricane Center wrote in a Thursday morning advisory. “Harvey has intensified quickly this morning, and is now forecast to be a major hurricane at landfall, bringing life-threatening storm surge, rainfall, and wind hazards to portions of the Texas coast.”

Harvey had disintegrated into a tropical depression as it crossed the Yucatán Peninsula into the western Gulf of Mexico this week. But it reorganized itself over the hot Gulf waters, forming a new, 15-mile-wide eye, and rapidly evolved into a hurricane by midday Thursday.

When it comes ashore, forecasters said, it could have sustained winds of 125 miles per hour, with a 12-foot storm surge.

1 of 74 Full Screen Autoplay Close Skip Ad × Southeast Texas prepares for expected landfall of Hurricane Harvey View Photos Tropical Storm Harvey intensified into a hurricane that forecasters said would be the first major hurricane to hit Texas in nine years. Caption The hurricane, which has weakened to a tropical storm, is the first Category 4 storm to hit the United States since Charley in 2004. Harvey has destroyed homes, severed power supplies and caused severe flooding. Aug. 27, 2017 Two kayakers try to beat the current of an overflowing Brays Bayou in Houston. Rescuers answered hundreds of calls for help as floodwaters from the remnants of Hurricane Harvey began to fill second-story homes. Mark Mulligan/AP Buy Photo Wait 1 second to continue.

Worse, it is projected to stall on the Texas coast for several days, which could dump historic quantities of rain, with some places seeing as much as 35 inches, the hurricane center said.

The storm is forecast to meander to the east, deluging Houston and possibly New Orleans next week.

Officials in Corpus Christi scrambled Thursday to respond to the sudden hurricane threat but decided against mandatory evacuations. Instead, officials instructed residents on the barrier island and low-lying areas inland to evacuate on a voluntary basis.

“We are up to and almost at the threshold of mandatory evacuations, but we are not going to cross that line right now,” McComb said. “We are going in the strongest possible terms to encourage the residents in the low-lying areas, as they say, ‘Get out of Dodge.’ ”

Nueces County Judge Samuel L. Neal, who is overseeing the county’s emergency response, did not rule out mandatory evacuations but said such a move would not be done lightly.

“We will do it if we feel it’s necessary,” he said. “This would create a major, major impact on the way a lot of people do business.”

Texas Gov. Greg Abbott (R) declared a preemptive state of disaster in 30 counties, including Harris County, home to Houston, the fourth most-populated city in the country. Charles Bujan, mayor of the barrier-island city of Port Aransas, Tex., ordered all citizens to evacuate except those working as emergency responders.

Long has stressed in interviews with The Washington Post that state and local officials need to improve their emergency readiness and recognize that it is not the federal government’s responsibility alone to respond to natural disasters.

Long has also urged citizens to understand that they will often be their own first responders in a crisis.

“People need to be the help before the help arrives,” he said earlier this month.

Long met with New Orleans Mayor Mitch Landrieu and Louisiana Gov. John Bel Edwards (D) on Tuesday and discussed preparations for hurricane season and the Aug. 5 flooding in New Orleans.

“Preparedness is a partnership between the local, state and federal level,” Long said. “Here, there is great concern over the city of New Orleans’s ability to pump water out of the so-called bowl.”

The city has 120 water pumps, but currently only 105 are operational, said Tyronne Walker, communications director for Landrieu. He said the city has brought in 26 generators to provide electricity during an emergency.

“Right now, there’s no reason to panic, but you know, everybody should just be focused on getting their plans in order,” Walker said. “While we’re in a stronger position than we were in the last drainage incident, we’re still vulnerable.”

Harvey would be the first hurricane to hit Texas since Ike, a high Category 2 storm, came ashore in September 2008 in Galveston and caused tens of billions of dollars in property damage.

In Corpus Christi, some residents on Thursday left work early to begin preparing their homes, while others headed out of town or contemplated hitting the road before the storm arrived.

“Everybody’s just trying to get away from this area right now,” said Ricky Nesmith, the kitchen manager at Blackbeard’s On the Beach.

Nesmith said a full staff came into the restaurant Thursday morning, but most workers left early to get their homes ready. The looming storm has not slowed business, Nesmith said, saying that large groups kept the restaurant busy Thursday before the owner decided to close up shop early.

Bill Sissamis, who owns the Silverado Smokehouse, a barbecue restaurant about two miles from the water, said that he would stay open as long as the weather allows.

“We do tend to get a lot of false alarms here,” said Sissamis, 54, of previous storm warnings, adding, “The city goes a little bit nuts.”

The Gulf of Mexico is vitally important for the nation’s oil infrastructure. Offshore platforms produce about 1.7 million barrels a day, nearly a fifth of U.S. crude oil production. More than 45 percent of U.S. petroleum refining capacity lies along the Gulf Coast as well as 51 percent of total U.S. natural gas processing plant capacity, according to Energy Department data.

ExxonMobil said at noon Thursday that it was already reducing production at its Hoover oil and gas platform in the Gulf of Mexico about 200 miles south of Houston and was evacuating personnel working offshore.

Shell said that it had evacuated about 200 offshore workers by helicopter and that it had shut in production and secured equipment at its deepwater Perdido oil and gas production hub. Two other platforms continued to operate as of Thursday night.

A Citigroup report to investors said more than 85 percent of Texas’s refining capacity is located inside the highest precipitation zone for the storm.

joel.achenbach@washpost.com

Mark Berman, Tim Craig, Brian McNoldy and Brian Murphy contributed to this report.