Trees toppled as the storm lingered for hours over Haiti's poor, deforested southern peninsula, and water levels were rising in banana, bean and vegetable fields. One man was killed in a landslide in the mountain town of Benet, civil protection director Marie Alta Jean-Baptiste told Radio Metropole.
"If the rain continues, we'll be flooded," U.N. food consultant Jean Gardy said from the southeastern town of Marigot.
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 to the nation's crops on Tuesday because of Haiti's poor infrastructure and faulty communications.
Oil prices shot up $5 a barrel Tuesday after the National Hurricane Center predicted Gustav could enter the gulf as a major hurricane this weekend. Prices of futures in natural gas, heating oil and gasoline also rose.
If Gustav 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.
"Most indications are that Gustav will be an extremely dangerous hurricane in the northwestern Caribbean Sea in a few days," the Miami-based hurricane center said.
Gustav roared ashore Tuesday afternoon near the city of Jacmel with top sustained winds near 90 mph. Heavy rains pelted the area as winds bent palm trees and kicked up surf along waterfronts of dilapidated wooden buildings.
Patrice Tallyrand, 43, fled with his family to a friend's home after Gustav knocked down four trees in their back yard in the southern town of Kabik.
"We had to leave the house before it got worse," he said.
Forty miles to the north, residents in the capital wrapped themselves in plastic sheeting against the rain and wind as they ran home in advance of the storm. Businesses closed early, and stranded travelers mobbed the American Airlines counter at the airport 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.
Forecasters said Gustav should slice along the southern coast of Cuba all week and grow into a perilous Category 3 hurricane with 120 mph winds before entering the central gulf on Sunday. Forecasters were reluctant to predict the storm's path beyond the weekend, the third anniversary of Hurricane Katrina.
A powerful storm in the gulf could force shutdowns on the offshore rigs that account for a quarter of U.S. crude production and much of its natural gas. Royal Dutch Shell PLC said it could begin evacuating workers as soon as Wednesday.
The U.S. military base at Guantanamo Bay, Cuba, had been expecting a direct hit, but later forecasts suggested the fiercest winds and rain will pass offshore. Base spokesman Bruce Lloyd said they were preparing for emergencies in any case.
More than 4,000 people were evacuated from their homes in the Dominican Republic, while in Jamaica, officials alerted shelters to prepare for possible evacuations Wednesday.