Updated

Thousands of people were ordered to evacuate the Texas and Louisiana coasts Tuesday as Laura strengthened into a hurricane that forecasters said could slam into land as a major storm with ferocious winds and deadly flooding.

More than 385,000 residents were told to flee the Texas cities of Beaumont, Galveston and Port Arthur, and still more were ordered to evacuate low-lying southwestern Louisiana, where forecasters said more than 11 feet of storm surge topped by waves could submerge entire towns.

“Heads up! Today is the last day to prepare for Hurricane #Laura. Evacuation zones are based on potential storm surge. If an evacuation has been ordered, life-threatening storm surge is expected. Get your loved ones to a safe place...their life depends on it!” the National Weather Service tweeted.

LAURA MOVING ACROSS GULF OF MEXICO, PROMPTING HURRICANE AND STORM SURGE WARNINGS

Laura was upgraded from a tropical storm to a Category 1 hurricane Tuesday and is expected to make landfall late Wednesday or early Thursday as a Category 3 hurricane, with winds of around 115 mph, according to the weather service.

Houston was not placed under an evacuation order as of noon Tuesday, and city officials urged residents to stay off the roadways to create a clear passage for those fleeing the shoreline, KTRK reported. Residents were also urged to fill up their gas tanks as soon as possible and gather enough supplies should they lose power over the next couple of days.

Some residents are still struggling to recover from Hurricane Harvey in 2017.

In Galveston and Port Arthur mandatory evacuation orders went into effect at 6 a.m. Tuesday. People planning on entering official shelters were told to bring just one bag of personal belongings each, and “have a mask” to reduce the spread of coronavirus.

Judge Lina Hidalgo emphasized that Laura should not be compared to past hurricanes like Harvey while addressing the media from Houston Transtar on Monday, Aug. 24, 2020. (Hadley Chittum /Houston Chronicle via AP)

Judge Lina Hidalgo emphasized that Laura should not be compared to past hurricanes like Harvey while addressing the media from Houston Transtar on Monday, Aug. 24, 2020. (Hadley Chittum /Houston Chronicle via AP)

Forecasters said ocean water could push onto land along a more than 450-mile-long stretch of coastline from Texas to Mississippi. Hurricane warnings were issued from San Luis Pass, Texas, to Intracoastal City, La.; and storm surge warnings from the Port Arthur flood protection system to the mouth of the Mississippi River.

State emergencies were declared in Louisiana and Mississippi, and shelters opened with cots set farther apart, among other measures designed to curb infections.

Cesar Reyes, right, carries a sheet of plywood to cut to size as he and Robert Aparicio, left, install window coverings at Strand Brass and Christmas on the Strand, 2115 Strand St., in Galveston on Monday, Aug. 24, 2020. ( Jennifer Reynolds/The Galveston County Daily News via AP)

Cesar Reyes, right, carries a sheet of plywood to cut to size as he and Robert Aparicio, left, install window coverings at Strand Brass and Christmas on the Strand, 2115 Strand St., in Galveston on Monday, Aug. 24, 2020. ( Jennifer Reynolds/The Galveston County Daily News via AP)

Laura's unwelcome arrival comes just days before the Aug. 29 anniversary of Hurricane Katrina, which breached the levees in New Orleans, flattened much of the Mississippi coast and killed as many as 1,800 people in 2005. Hurricane Rita then struck southwest Louisiana that Sept. 24 as a Category 3 storm.

While crosswinds ripped apart Marco, which still doused the region with heavy rain, there was little to keep Laura from turbocharging. Nearly all the computer simulations that forecasters rely on show rapid strengthening at some point in the next couple of days.

Forecasters turned their attention to the Gulf Coast, where up to 11 feet of seawater — or a storm surge — could inundate the coastline from High Island in Texas to Morgan City, La., the hurricane center said.

On top of that, up to 15 inches of rain could fall in some spots in Louisiana, said Donald Jones, a National Weather Service meteorologist in Lake Charles, La. — in the bullseye of Laura’s projected path.

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Laura passed Cuba after killing nearly two dozen people on the island of Hispaniola, including 20 in Haiti and three in the Dominican Republic, where it knocked out power and caused intense flooding. The deaths reportedly included a 10-year-old girl whose home was hit by a tree and a mother and young son crushed by a collapsing wall.

The Associated Press contributed to this report.