From a tiny, vulnerable island off the Louisiana coast to the beaches of the Florida Panhandle, Gulf Coast residents prepared Thursday for a possible hit from tropical storm Karen, which threatened to become the first named tropical system to menace the United States this year.

Karen was forecast to lash the northern Gulf Coast over the weekend as a weak hurricane or tropical storm. A hurricane watch was in effect from Grand Isle, La., to west of Destin, Fla. A tropical storm warning was issued for the Louisiana coast from Grand Isle to the mouth of the Pearl River, including the New Orleans area.

State of emergency declared

In Alabama, safety workers hoisted double red flags at Gulf Shores because of treacherous rip currents ahead of the storm.

In Mississippi, Gov. Phil Bryant declared a state of emergency, urging residents to prepare. State Emergency Management Agency director Robert Latham said local schools will decide whether to play football games. He said the southern part of the state could have tropical storm-force winds by late Friday.

"I know that Friday night football in the South is a big thing, but I don't think anybody wants to risk a life because of the potential winds," Latham said.

Louisiana Gov. Bobby Jindal also declared a state of emergency, citing the possibility of high winds, heavy rain and tides. Florida Gov. Rick Scott also declared an emergency for 18 counties.

TROPICAL STORM KAREN

Terry and Clair Canette of Biloxi, Miss., gas up their cars at the Clark's Shell station on Cedar Lake Road in Biloxi in preparation for Tropical Storm Karen on Thursday Oct. 3, 2013. (John Fitzhugh, Sun Herald/Associated Press )

The Army Corps of Engineers said it was closing a structure intended to keep storm surge out of the Inner Harbor Navigation Canal in Louisiana — known locally as the Industrial Canal — where levee breaches during Hurricane Katrina led to catastrophic flooding in 2005.

Mayor David Camardelle of Grand Isle, La., an inhabited barrier island and tourist town almost 100 kilometres south of New Orleans, called for voluntary evacuations as he declared an emergency Thursday afternoon.

Louisiana officials were taking precautions while noting that forecasts show the storm veering to the east. The storm track had it likely brushing the southeastern tip of the state before heading toward the Alabama-Florida coast. And it was moving faster than last year's Hurricane Isaac, a weak storm that stalled over the area and caused widespread flooding.

"It should make that fork right and move out very, very quickly," said Jerry Sneed, head of New Orleans' emergency preparedness office.

Offshore, at least two oil companies said they were evacuating non-essential personnel and securing rigs and platforms.

Some furloughed workers recalled

In Washington, the White House said the Federal Emergency Management Agency was recalling some workers furloughed due to the government shutdown to prepare for the storm.

White House spokesman Jay Carney said President Barack Obama was being updated about the storm. He said Obama directed his team to ensure staffing and resources are available to respond to the storm.

Hundreds of thousands of federal workers have been furloughed under the partial government shutdown. It's unclear how many FEMA workers are being brought back.

The National Hurricane Center in Miami said Karen was about 579 kilometres south of the mouth of the Mississippi River Thursday evening and had maximum sustained winds of 100 km/h with higher gusts. The storm was moving north-northwest at 19 km/h. It could be at or near hurricane strength late Friday and early Saturday, forecasters said, with the centre near the coast on Saturday.

Storm could weaken near coast

While meteorologists said it was too soon to predict the storm's ultimate intensity, they said it could weaken a bit as it approaches the coast over the weekend.

"Our forecast calls for it to be right around the border of a hurricane and a tropical storm," said David Zelinsky, a hurricane center meteorologist.

Whether it's a weak hurricane or strong tropical storm, Karen's effects are expected to be largely the same: Heavy rain with the potential for similar storm surge.

Forecasters say Karen is expected to bring 100 to 200 millimetres of rain to portions of the central and eastern Gulf Coast through Sunday night, mainly near and to the right of the path of the centre.

Camardelle, whose vulnerable island is often the first to order an evacuation in the face of a tropical weather system, said the town is making sure its 10 pump stations are ready. He encouraged residents to clean out drainage culverts and ditches in anticipation of possible heavy rain and high tides.