The U.S. National Hurricane Center in Miami said the storm could regain hurricane strength soon and forecasts suggested it could head toward the U.S. Gulf Coast as a dangerous Category 3 hurricane next week.
That could mean higher gasoline prices for drivers around the world. Global oil prices rose by $1.40 early Wednesday to above $117 a barrel on concerns the storm could disrupt output in the Gulf, home to a quarter of U.S. crude production.
Royal Dutch Shell PLC said it could begin evacuating workers as soon as Wednesday.
If the storm continues on its path, it could drive up U.S. gasoline prices by 10 cents a gallon ahead of Labor Day weekend, predicted James Cordier, president of Tampa, Florida-based Liberty Trading Group and OptionSellers.com.
Gustav's maximum sustained winds were near 60 mph Wednesday morning, with higher gusts. The storm was centered about 90 miles west of Port-au-Prince and was expected to continue moving toward the west-northwest.
A hurricane warning was in effect for parts of Cuba, including the U.S. military base at Guantanamo Bay, and base spokesman Bruce Lloyd said it was preparing for any emergencies.
Jamaica issued a tropical storm warning Wednesday and also remained under a hurricane watch along with the Cayman Islands. A watch means hurricane conditions are possible within 36 hours.
As a hurricane, Gustav caused a deadly landslide and dumped torrential rains on southern Haiti, which is prone to devastating floods because its mountainous terrain has been stripped of trees for farming and charcoal.
At least eleven people have been confirmed dead due to the storm, including a man killed in a landslide in the mountain town of Benet, civil protection director Marie Alta Jean-Baptiste said.
Eight people died in a landslide in the Dominican Republic capital of Santa Domingo. The civil defense agency director Luis Luna Paulino said the victims who died overnight were members of one family. He said more than 5,000 people across the country have been evacuated as a result of the storm.
Details about the other deaths were not immediately available.
Hundreds have been driven from their homes by flooding. Rising waters surrounded palm trees near the southern coast city of Jacmel that had been kicked over by the storm and reached the city's trademark Victorian-style wooden buildings.
The storm lingered into the night over Haiti's poor, deforested southern peninsula, and water levels were rising in banana, bean and vegetable fields. Cars pushed through standing water in the streets of Port-au-Prince, as fallen trees and landslides blocked a major road out of the capital.
Hundreds of people in coastal Les Cayes ignored government warnings to seek shelter, instead throwing rocks to protest the high cost of living in the Western Hemisphere's poorest country. Witnesses said U.N. peacekeepers used tear gas to disperse the crowd.
Haiti is a tinderbox because of soaring food prices, which in April led to deadly protests and the ouster of the nation's prime minister. It was difficult to ascertain the extent of the damage from the hurricane to the nation's crops on Tuesday because of Haiti's poor infrastructure and faulty communications.
"If the rain continues, we'll be flooded," U.N. food consultant Jean Gardy said Tuesday from the southeastern town of Marigot.
At Port-au-Prince's airport, stranded travelers mobbed the American Airlines counter, desperate to rebook tickets after the airline canceled all flights.
"I knew it was coming, but I was hoping to be out before it came," said Jody Stoltzfus, a 27-year-old missionary who had planned a visit home to Lancaster, Pennsylvania.