By Madeline Holcombe, Eric Levenson and Judson Jones, CNN

(CNN) -- After battering western Cuba as a tropical storm, Laura has strengthened into a hurricane in the Gulf Coast and is expected to grow even stronger as it heads toward Texas and Louisiana.

Hurricane Laura currently has maximum sustained winds of 75 mph, according to data from a NOAA hurricane hunter plane, and is likely to become a major Category 3 storm or higher over the next day or so. The center of the storm is located 620 miles from Galveston, Texas, and it's moving at a rapid clip of 16 mph.

A hurricane warning has been issued for portions of the Texas and Louisiana coastline, according to the National Hurricane Center. The warning, an upgrade from the earlier hurricane watch, stretches from San Luis Pass, Texas, through Intracoastal City, Louisiana.

The warning includes Galveston and Galveston Bay, as well as portions of the Houston metro area, and stretches across Texas's northeast coast and the western half of Louisiana's coastline.

The NHC warned that Laura is expected to produce 4 to 8 inches of rain from Wednesday night into Saturday, with isolated maximum amounts of 12 inches across parts of the Gulf Coast. This could cause widespread flash and urban flooding, the NHC said.

Laura's impending arrival comes as the Gulf Coast avoided a powerful storm in Marco, which significantly weakened before reaching the US.

As a Tropical Storm, Laura killed at least nine people in the Caribbean. When it makes landfall in the US, it could bring storm surge of 7 to 11 feet along portions of the coast, the NHC said.

Houston is particularly vulnerable

Houston, the largest city in the region, is particularly vulnerable. The concrete-filled city has notoriously poor drainage systems and a propensity to flood, such as during the overwhelming rainfall from Hurricane Harvey in 2017.

Laura's potential path and rapid intensification bears closer resemblance to Hurricane Rita in September 2005, the last time a major hurricane made landfall in Louisiana. Rita came just a month after Hurricane Katrina devastated the region, and its impending approach caused mass evacuations and gridlock on Texas highways.

More than 100 people died in Texas due to the evacuation, including 24 nursing home evacuees aboard a bus that caught fire and exploded.

The threat of Hurricane Laura has already sparked evacuations in Texas. Galveston issued a mandatory evacuation order for all residents on Tuesday morning, according to a post on the city website. All city service will be suspended at noon Tuesday.

"With the uncertainties of this story and its increasing strength, we need to take all necessary precautions to protect our residents," Galveston Mayor Pro Tem Craig Brown said in a press release.

A mandatory evacuation order was issued for all residents of Jefferson County, Texas, Monday, according to the county's Office of Emergency Management's Facebook page. And Orange County, Texas, has recommended a voluntary evacuation for the entire county ahead of Tropical Storm Laura.

With Marco no longer posing an impending threat, Louisiana Gov. John Bel Edwards said Monday night all eyes are now on Laura. His big concern was large amounts of rainfall and river flooding.

"There will be storm surge impact, there will be wind impact, there will be rain impact," the governor said.

In Louisiana, residents have been preparing for the storms as well. Long lines formed outside grocery stores on Monday in Louisiana as residents braced for both Marco and Laura.

Stacie Osborn said it took her 30 minutes just to get through the checkout line at a market in New Orleans.

"I stocked up on enough food for the week, extra water and gassed up my car just in case," she said.

And New Orleans Mayor LaToya Cantrell said the site of the Hard Rock Hotel, which collapsed during construction in October last year, remains a public safety risk because of the building's instability. Three people died and dozens were injured during the collapse. It took some 10 months to recover two of the bodies because of the structure's instability.

Marco downgraded to tropical depression

The Gulf was predicted to be in danger of back-to-back powerful storms with Laura striking within miles and 48 hours after Marco.

Edwards worried earlier in the week that "there may not be much of a window" to enact power restoration and rescue efforts between storms.

But Marco made landfall near the mouth of the Mississippi River Monday as a tropical storm, and later that night was downgraded once more to a tropical depression.

Overnight, Marco was traveling west along the Louisiana shoreline, but it will likely fizzle out over open waters as it heads toward Texas, said CNN meteorologist Michael Guy.

The tornadoes and storm surge that Marco threatened to bring along with it as it moved along the Gulf Coast are no longer a source of concern, Guy said. However, the storm could still be a rainmaker, and localized areas could see up to five inches of precipitation.

9 people killed in the Caribbean

At least nine people have died in the Caribbean, including several in the Dominican Republic and Haiti, due to Laura.

The victims include a 7-year-old boy who died along with his mother after a wall collapsed in their home in the Dominican Republic. Another person died after a tree fell on a house.

Dominican Republic President Luis Abinader said an army corporal was killed while helping with rescue efforts in Pedernales province.

Five people were killed in Haiti, including a 10-year-old girl, the country's civil protection agency said.