The leading edge of Tropical Storm Gordon hurled rough surf, gusty winds and heavy rain at parts of the US Gulf Coast on Tuesday afternoon, hours before it was due to make landfall, possibly as a hurricane, forecasters said.
The storm caused global oil prices to rise after two oil platforms in the Gulf of Mexico were evacuated.
Gordon was due to come ashore late on Tuesday near the border between Louisiana and Mississippi, and drop as much as 12 inches (30 cm) of rain in areas still recovering from last year's powerful hurricanes, the National Hurricane Center said.
Louisiana Governor John Bel Edwards declared a state of emergency.
Winds of about 65 miles per hour (105 km per hour) in the afternoon were expected to reach hurricane force of at least 74 mph (119 kph) by the time storm reaches the Gulf Coast.
"I’m asking all residents to do their part in getting ready for this storm," New Orleans Mayor LaToya Cantrell said in a statement. "The City’s absolute number one priority is to ensure the safety of our residents."
Beaches around Mobile, Alabama, were being washed by storm-driven waves on Tuesday morning, said Stephen Miller, a meteorologist for the National Weather Service.
"We're expecting an increase in winds," Miller said in a telephone interview. "We could see flooding."
Outer rainbands of the storm were producing gusty winds and heavy rain along the coast of the western Florida Panhandle, the National Hurricane Center said in an afternoon advisory.
Sea levels could rise as much as 1.5 metres from Shell Beach, Louisiana, to Dauphin Island, Alabama, forecasters said.
The Mississippi Emergency Management Agency told South Mississippi residents to be prepared to evacuate.
Get ready
As of Tuesday afternoon, Gordon was about 130 miles (205 km) south-southeast of Mobile, Alabama, about 145 miles southeast of Biloxi, Mississippi, and heading west-northwest, according to the National Hurricane Center.
Chuck Lamey, owner of Pops Pizzeria in Biloxi, Mississippi, said he planned to close by 3 pm instead of 9 pm on Tuesday before the storm hits land.
"We're hoping to open at regular time tomorrow at 11 o' clock, but if it's still a threat we'll postpone the opening," Lamey said. "We want the employees to be safe and have time to prepare."
US oil producer Anadarko Petroleum Corp evacuated workers and shut production at two offshore oil platforms on Monday, and other companies with production and refining operations along the Gulf Coast said they were securing facilities.
The Gulf of Mexico is home to 17 per cent of US crude oil and 5 per cent of natural gas output daily, according to the US Energy Information Administration.
The US Coast Guard said the ports of New Orleans and Gulfport and Pascagoula, Mississippi, may have to close within 48 hours.
Last year, hurricanes hit Texas, Florida and Puerto Rico, causing widespread destruction and thousands of deaths.
Gordon was expected to weaken rapidly after moving ashore, forecasters said.
The Inn at Ocean Springs and The Roost Hotel in Ocean Springs, Mississippi, had guests planning to ride out the storm, said Kristin Smith, general manager of both hotels.
"A lot of guests are real comfortable sticking it out in our rooms," Smith said in a telephone interview. "Any of our guests who feel like they want to go home we encourage them to follow their instincts."