With forecasts showing Ike blowing ashore this weekend, authorities lined up nearly 1,000 buses in case they are needed to move out the many poor and elderly people who have no cars.
Federal authorities gave assurances they would not check people's immigration status at evacuation loading zones or inland checkpoints. But residents were skeptical, and there were worries that many illegal immigrants would refuse to board buses and go to shelters for fear of getting arrested and deported.
"People are nervous," said the Rev. Michael Seifert, a Roman Catholic priest and immigrant advocate. "The message that was given to me was that it's going to be a real problem."
One reason for the skepticism: Back in May, Homeland Security Secretary Michael Chertoff said the Border Patrol would do nothing to impede an evacuation in the event of a hurricane. But when Hurricane Dolly struck the Rio Grande Valley in late July, no mandatory evacuation was ordered, and as a result the Border Patrol kept its checkpoints open. Agents soon caught a van load of illegal immigrants.
It would be the first mandatory large-scale evacuation in South Texas history. State and county officials let people decide for themselves whether to leave a hurricane area until just before Hurricane Rita struck the Gulf Coast in 2005. Now county officials can order people out of harm's way.
Hidalgo County Judge J.D. Salinas said if an evacuation is ordered this time, county officials will visit immigrant neighborhoods and forcefully urge people to clear out.
After Hurricanes Katrina and Gustav, "there were a lot of immigrants who said, `I'm not going to go,"' said Salinas, the county's top elected official. "It's going to be hard."
In Washington, Rear Adm. W. Craig Vanderwagen, assistant U.S. health secretary for preparedness and response, told reporters: "In storm events, if people are trapped it doesn't particularly matter to those of us in the humanitarian assistance world which side of that border they come from. We will do what we need to do to evacuate the people who need to be evacuated."
At 8 p.m. EDT, Ike was about 95 miles west of Havana, Cuba, moving west-northwest at 10 mph with sustained winds near 75 mph.
It was expected to cross the Gulf of Mexico, strengthening to a Category 3 with winds of up to 130 mph.
Forecasters said that it could hit on Saturday morning just about anywhere along the Texas coast, with the most likely spot close to the Corpus Christi area.
Areas from Matagorda Bay to Corpus Christi and south to Brownsville - about 250 miles of coastline - were told to prepare for possible mandatory evacuation.
On Tuesday, Ike roared across Cuba, ravaging homes, killing at least four people and forcing 1.2 million to evacuate.
The Rio Grande Valley is still soggy from Dolly, which flooded the region, damaging hundreds of homes but killing no one. Many homes still have blue tarps on their roofs.
The Rio Grande Valley's residents are among those least equipped to handle hurricane flooding. It is one of the poorest parts of the country, with one-third of all families living below the poverty line, compared with 10 percent nationally.
Colonias, or ramshackle communities often lacking sewer systems and paved streets, dot the Valley. Even an ordinary rainstorm can fill yards with disease-ridden sewage from flooded septic tanks. Many of the poor lack health insurance.
Mexican officials said more than a dozen dams in the northern state of Chihuahua were at capacity or spilling over, heightening fears of flooding on the American side of the border.
Gov. Rick Perry declared 88 coastal counties disaster areas Monday to start the flow of state aid, and began preparing for an evacuation, lining up "buses rather than body bags."
The Dallas-Fort Worth area sheltered about 3,000 Hurricane Gustav evacuees last week and is prepared for up to about 20,000 people this time, said Steve Griggs, a county official. The downtown convention center would again serve as the main shelter.
Associated Press writers Eileen Sullivan in Washington, April Castro in Austin, Texas, and Jeff Carlton in Dallas contributed to this report.