(CNN) -- Anticipating the possibility that Hurricane Ike might hit the Texas coast this weekend, the cities of Corpus Christi and Galveston warned residents Tuesday to plan.
The National Hurricane Center indicated Ike would likely come ashore along the Texas coast between Galveston and Brownsville as a major hurricane. But forecasters stressed the unpredictability of the storm, which could change course at the last minute.
"It's very frustrating for all of us," said Galveston Mayor Lyda Ann Thomas, adding, "We're on alert and we will continue to monitor this storm. I wish we could be clearer about where it's going."
Ike's center left western Cuba late Tuesday afternoon, having hit it with 75-mph winds, high surf and torrential rains in its second Cuban landfall in three days, the National Hurricane Center said.
At 5 a.m. ET Wednesday, Ike, with its 85-mph winds, was churning in the southeastern Gulf of Mexico, according to the center. The wind speed of the storm increased by 10 mph overnight.
Forecasters say Ike is likely to make landfall around Port O'Connor, Texas late Friday or early Saturday as a Category 3 hurricane, with winds of between 111-130 mph.
Tropical storm-force winds extended Tuesday to the Florida Keys. Storm-surge flooding of 1-to-3 feet beyond the normal tide levels was possible there, and large swells that could generate life-threatening rip currents were expected along the east coast of Florida into Wednesday, the hurricane center said. iReport.com: Big waves hit Florida Keys
Thomas warned residents to stock up on nonperishable items, including pet food and diapers, and to prepare for going without electricity. Track the storm
City Manager Steve LeBlanc issued a warning to residents of Galveston's West End, citing forecasters' estimates that the area could get tides of 6 feet above normal if the storm arrives there. The West End, he said, is the area of Galveston most susceptible to flooding.
Thomas said she could call for voluntary evacuations of the West End by Wednesday morning, depending on forecasts.
By Tuesday night, officials in Corpus Christi, Texas, had called for the evacuations of special-needs residents beginning Wednesday morning. They also called for the relocation of high-profile vehicles -- including vans, motor homes, travel trailers and hitched boats -- that could hinder traffic if expanded evacuations become necessary.
The Texas Department of Transportation said it expected to open a shoulder of northbound Interstate 37 to traffic -- from coastal Corpus Christi to U.S. 281 roughly 80 miles inland -- on Wednesday morning to help people trying to leave the city.
Texas Gov. Rick Perry put 7,500 National Guard members on standby Tuesday, his office said. Watch where Ike may be headed along U.S. coast »
In Cuba, evacuations appeared to save lives. Four deaths were reported from the storm, according to the Cuban government. The Cuban Civil Defense brought buses or trucks to take people to shelters. See the damage from the storm »
Cuban state television reported that two people were killed when they tried to remove an antenna, The Associated Press said. One man died when a tree crashed into his home, and a woman died when her home's roof collapsed, according to the AP.
The storm shredded hundreds of homes and caused some dilapidated buildings in Havana's older areas to collapse, the AP reported.
Teresa Tejeda, who is in her 70s, told the AP she joined several hundred other elderly people at a government shelter because she was too scared to stay in her old apartment building.
"My house has really bad walls, and I feel much more secure here," Tejeda said. Watch as winds and waves pound Cuba »
The United States, which provided $100,000 in emergency aid to communist-run Cuba through private aid agencies after Hurricane Gustav hit the island August 30, said Tuesday that it was considering additional emergency aid for Cuba because of Ike.
Also, the United States said it will lift restrictions on cash and humanitarian assistance sent to Cuba for the next 90 days. That will allow non-governmental organizations to provide assistance and cash donations.
Flooding and rains from Ike's outer bands have been blamed for 70 deaths in Haiti, bringing that country's death toll from four recent major storms -- including Fay, Gustav and Hanna -- to 341, said Abel Nazaire, deputy head of Haiti's Civil Protection Service.
On Sunday night, waves as high as 50 feet crashed ashore in Baracoa, Cuba, southeast of where Ike made landfall as a Category 3 storm. At least 1,000 homes were damaged or destroyed as the sea surge moved into the city, witnesses said. Watch what Ike did to Cuba »
An estimated 900,000 people left their homes ahead of Ike's arrival and went inland or to higher ground. Some of the evacuees were homeless after Gustav pounded western Cuba.
Residents on the western half of the island scrambled to get necessities before the worst of the storm hit, CNN's Morgan Neill reported from Havana.
Coastal storm surge flooding of 3 to 5 feet above normal tide levels and rainfall of 6 to 12 inches were possible in Cuba, the hurricane center said.
People in the capital were worried that Ike's heavy rain would bring flooding and landslides to the area and damage some of its more fragile infrastructure.
Many evacuees went to schools or government buildings with stronger roofs. The Cuban government cut power to the eastern half of the island before Ike arrived and canceled all domestic flights.
CNN's Karl Penhaul, Morgan Neill, April Williams and Charley Keyes contributed to this report.
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