Hurricane Harvey made landfall Friday night between Port Aransas and Port O'Connor, Texas, as a Category 4 storm with winds of 130 mph, the National Hurricane Center said.
Harvey is the first Category 4 hurricane to make landfall in the United States since Hurricane Charley in 2004.
The storm is poundng the Texas coast and its millions of residents with hurricane-force winds knocking down trees, power poles and signs, and with torrential rain deluging streets.
In its 11 p.m. ET update, the National Hurricane Center said the center of the storm had passed over San Jose Island, bringing with it a dangerous and powerful eye wall.
The hurricane center warns that some areas will see as much as 13 feet of storm surge and large, destructive waves.
And there's the rain that the slow-moving storm is expected to produce. Because it is expected to come to a near halt inland, Harvey could drop as much as 40 inches of rain in some places, and up to 30 inches in others, by Wednesday.
The combination of wind and water could leave wide swaths of South Texas "uninhabitable for weeks or months," the National Weather Service in Houston said.
Such daunting language hasn't been seen by CNN's experts since Hurricane Katrina, which left more than 1,800 people dead in 2005.
The threat has prompted officials in at least one town to ask residents who stay behind to write their Social Security numbers on one of their arms in case. It will make identifying bodies easier.
"Texas is about to have a very significant disaster," said Brock Long, director of the Federal Emergency Management Agency.
Gov. Greg Abbott warned of record-setting flooding and called on people to flee the area before the storm hits.
"My top goal is to be able to make it through this storm in a way in which we lose no lives," Abbott said. "Put your life first and your property second."
Residents were urged to evacuate. A mass exodus from the coast caused extensive traffic jams along the state's highways, while other people boarded up windows and stocked up on food and water ahead of the storm, the effects of which are expected to last for days.
The storm will stall and dump rain on South Texas and parts of Louisiana into the middle of next week, forecasters predicted.
-- Rockport, Texas, officials are advising residents who refuse to evacuate to write their names and Social Security number on a forearm, Mayor Pro Tem Patrick Rios told CNN. Rios said it will "help out first responders should they find a body."
-- The National Weather Service in Corpus Christi issued an extreme wind warning for portions of the Texas coast. "Widespread destructive winds of 115 to 145 mph will produce swaths of tornado-like damage," the agency said.
-- Texas' governor requested additional federal help with a presidential disaster declaration. The White House is considering the declaration.
-- President Donald Trump, who will visit the area next week, has signed a disaster declaration for the state.
FEMA prepared for 'significant disaster'
Those who stay should "elevate and get into a structure that can withstand potentially Category 3 winds from a hurricane," said Long, the FEMA director.
"The bottom line message is, right now, if people have not heeded the warning, again, their window to do so is closing," Long said. "If they refuse to heed the warning, that's on them."
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Long said he is "very worried" about storm surge, or "wind-driven water," slamming coastal areas, saying it has the "highest potential to kill the most amount of people and cause the most amount of damage."
Trump tweeted that he has spoken with the governors of Texas and Louisiana, saying he is "closely monitoring Hurricane Harvey developments and here to assist as needed."
Record flooding expected
Officials worried that Harvey's deluge of rain will drench Texas and the region for several days.
"We could see this storm park for almost five days in some places, and we hear three feet of rain," said Bill Read, the former director of the National Hurricane Center. "That's just going to be a huge problem for these areas."
"The water is going to be the issue," Corpus Christi Mayor Joe McComb said. "We've never had anything like this."
Harvey is also causing concern in New Orleans, where heavy rain could usher in as much as 20 inches of rain through early next week and overwhelm the city's already-compromised drainage system.
Storm nears shore
Joey Walker, 25, works with the Galveston Island Beach Patrol and is riding out the storm from a house on Galveston Island. He posted video of near-white out conditions overlooking Stewart Beach.
Houston Mayor Sylvester Turner said anyone not leaving should plan to stay off the roads once the storm starts.
"People need to know, this is not a one-, two-day event and done," Turner said.
'I'm trying to be strong'
The threat of Harvey became evident Thursday when several coastal Texas counties issued evacuation orders, leading to hordes of residents sitting bumper to bumper for miles.
Rose Yepez told CNN it took her twice as long as usual to drive 140 miles from Corpus Christi to San Antonio, en route to Texas Hill Country.
Private vehicles -- along with city buses packed with adults and children carrying backpacks -- jammed roads for hours.
"I'm shaking inside, but for them, I'm trying to be strong," a Corpus Christi woman who was waiting with her two daughters to board a bus out of town told CNN affiliate KRIS.
Workers at 39 offshore petroleum production platforms and an oil rig in the Gulf of Mexico also evacuated Thursday, the Bureau of Safety and Environmental Enforcement said.
First responders such as Brittany Fowler stayed behind and waited for the storm.
"Hopefully, it doesn't do any damage, but if it does, we've prepared," Fowler, a firefighter in Corpus Christi, wrote on Instagram.
Fowler's family helped by boarding up windows and doors at her home, and she bought plenty of water, food and a small power generator.
Despite the warnings, Elsie and David Reichenbacher prepped supplies and planned to stay put in Corpus Christi.
"I've gone through a lot of hurricanes. I've lived here most of my life," Elsie Reichenbacher said. "I'd rather take care of my home and my animals and be safe here. I'm on high ground with my house."
CNN's Joe Sterling, Amanda Jackson, Matt Rehbein, AnneClaire Stapleton, Dakin Andone, David Williams, David Shortell, Eliott C. McLaughlin, Nick Valencia and Keith Allen contributed to this report.