KEY WEST, Fla. - Thousands of residents fled the Florida Keys as Tropical Storm Rita barreled toward the island chain, poised to grow into a hurricane with a potential 9-foot storm surge and sparking fears it could eventually ravage the hobbled Gulf Coast.

South Floridians kept a wary eye on Rita, which threatened to arrive today and drop up to 15 inches of rain on some parts of the low-lying Keys. Oil prices surged on the possibility that oil and gas production would be interrupted once again.

"I've lived in Florida all my life," said James Swindell, 37, who shopped along a cleared-out Miami Beach on Monday. "You always have to be worried about a storm, because they are too unpredictable and they can shift on you at the last minute. Nobody knows what they are going to do."

The storm had top sustained winds of 70 mph early today, and it was expected to strengthen into a Category 1 hurricane, with winds of at least 74 mph, as it approached the Keys. The storm's outer rain bands began drenching the Keys and Miami-Dade County early today after felling trees in the Bahamas.

"The main concern now is the Florida Keys," said Max Mayfield, director of the National Hurricane Center in Miami. "It's moving over very warm water and that's extremely favorable for development."

Hurricane warnings were posted for the Keys and Miami-Dade County, the hurricane center said. Residents and visitors were ordered to clear out of the Keys, and voluntary evacuation orders were posted for some 134,000 Miami-Dade residents of coastal areas such as Miami Beach.

"We're just trying to get enough gas to get home," said Andres Sweeting, 29, of Miami, as he stopped at a Coconut Grove gas station with his family. Long lines of customers had depleted two of the station's four gasoline tanks.

Forecasters said 3 to 5 inches of rain was possible across southern Florida. A storm surge rising 6 to 9 feet above normal tide level was predicted for the Keys.

In the Bahamas, no serious damage was reported after Rita passed to the south. However, fishermen had dragged their boats to dry land and some people shuttered their windows - a sign that normally laid-back islanders had been concerned about the storm.

Officials in Galveston, Texas - nearly 900 miles from Key West - were already calling for a voluntary evacuation. Forecasters said Rita could make landfall in Mexico or Texas by the weekend, with a possibility that it could turn toward Louisiana.

Louisiana Gov. Kathleen Blanco urged everyone in the southwest part of the state to prepare to evacuate. "If Rita passes us by, we will thank the Lord for our blessings," Blanco told the state's storm-weary residents in a televised address.

Rita is the 17th named storm of the Atlantic hurricane season, making this the fourth-busiest season since record-keeping started in 1851. The record is 21 tropical storms in 1933. Six hurricanes have hit Florida in the last 13 months.