KINGSTON, Jamaica — Residents, tourists and oil workers fled as Gustav swamped Jamaica today, leaving 59 people dead in its wake. Louisiana and Texas put their national guards on standby, and New Orleans said a mandatory evacuation might be necessary.

At least 51 people died in Haiti from floods, mudslides and falling trees, including 25 around the city of Jacmel, where Gustav first struck land Tuesday. Eight more people were buried when a cliff gave way in the Dominican Republic. Marcelina Feliz died clutching her 11-month-old baby. Five more of her children were smothered in the wreckage beside her.

This afternoon, Gustav was 40 miles (65 kms) off Jamaica but already lashing the island with tropical storm-force winds. Forecasters said it could grow to a hurricane before hitting the low-lying capital of Kingston tonight. Grand Cayman braced for a possible strike a day later.

Even as tourists searched for flights off the islands, officials urged calm. One of the owners of the Grand Caymanian Resort, Theresa Foster, said Gustav didn’t look as threatening as Hurricane Ivan, which destroyed 70% of Grand Cayman’s buildings four years ago.

“Whatever was going to blow away has already blown away,” she said.

Forecasters said parts of Jamaica could get 25 inches (63 centimeters) of rain, which could trigger landslides and cause serious crop damage. Authorities told fisherman to stay ashore, and hotel workers secured beach umbrellas in the resort city of Montego Bay.

Jamaica ordered residents to evacuate low-lying areas including Portmore, a crowded and flood-prone area outside Kingston, and move into shelters. Kingston’s main airport was closed and buses stopped running even as people streamed into supermarkets for emergency supplies.

Oil prices jumped above $120 a barrel on fears that the storm could affect production in the Gulf area, home to 4,000 oil rigs and half of America’s refining capacity. Hundreds of offshore workers pulled out as analysts said the storm could send American gas prices back over $4 a gallon.

“Prices are going to go up pretty soon. You’re going to see increases by 5, 10, 15 cents a gallon,” the publisher of the Oil Price Information Service in Wall, N.J., Tom Kloza, said. “If we have a Katrina-type event, you’re talking about gas prices going up another 30 percent.”

In the Atlantic, meanwhile, Tropical Storm Hanna formed on a course that pointed toward the American east coast. It was too early to predict whether Hanna could threaten land, but Gustav was causing jitters from Mexico’s Cancun resort to the Florida panhandle.

With top sustained winds just below hurricane strength, Gustav was projected to become a major Category 3 hurricane after passing between Cuba and Mexico and entering the warm and deep Gulf waters. Some models showed Gustav taking a path toward Louisiana and other Gulf states devastated by hurricanes Katrina and Rita.

Louisiana Governor Bobby Jindal declared a state of emergency to lay the groundwork for federal assistance. Texas Governor Rick Perry issued a disaster declaration, and together they put 8,000 National Guard troops on standby.

New Orleans Mayor Ray Nagin said he would order a mandatory evacuation of the city if forecasters predict a Category-3 strike — or possibly even a Category-2 — within 72 hours.

Both Mr. Jindal and Mr. Nagin were meeting with the U.S. Homeland Security Secretary, Michael Chertoff, to plan.

“I’m panicking,” said Evelyn Fuselier of Chalmette, whose home was submerged in 14 feet (4 meters) of Katrina’s floodwaters. “I keep thinking, ‘Did the Corps fix the levees?,’ ‘Is my house going to flood again?’ … ‘Am I going to have to go through all this again?'”

In Gustav’s wake, Haitians struggled to find affordable food. An 18-year-old banana grower, Jean Ramando, said winds tore down a dozen of his family’s banana trees, so he was doubling his price.

“The wind blew them down quickly, so we need to make some money quickly,” he said.