By MICHAEL KUNZELMAN and KEVIN McGILL Associated Press

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.

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 and state Emergency Management Agency Director Robert Latham urged coastal residents to be prepared. 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 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.

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, an inhabited barrier island and tourist town about 60 miles 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.

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.

The National Hurricane Center in Miami said Karen was about 400 miles (644 kilometers) south of the mouth of the Mississippi River Thursday evening and had maximum sustained winds of 65 mph (100 kph) with higher gusts. The storm was moving north-northwest at 12 mph (19 kph). It could be at or near hurricane strength late Friday and early Saturday, forecasters said.

In Mexico's Caribbean coast state of Quintana, the brief passage of Karen before the storm moved north caused authorities to close seaports and some schools, but little rain was actually reported.

A few fishing camps and small hamlets along the coast were ordered evacuated late Wednesday, and some boat services were suspended for the estimated 35,000 tourists currently in Cancun. But the head of the Cancun Hotel Association, Roberto Cintron, said tourists appeared to be taking it in stride.

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 4 to 8 inches 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 center.

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.

"Hopefully, this one is just a little rain event," Camardelle said. "We don't need a big storm coming at us this late in the season."

Forecasters said a cold front approaching from the northwest was expected to turn Karen to the northeast, away from the Louisiana coast and more toward the Florida Panhandle or coastal Alabama. But the timing of the front's arrival over the weekend was uncertain.

Grand Isle suffered damage from Hurricane Isaac in August 2012. Isaac clipped the mouth of the Mississippi River for its official first landfall before meandering northwest over Grand Isle and stalling inland. Though a weak hurricane, Isaac's stall built a surge along the southeast Louisiana coast that flooded communities in neighboring Plaquemines Parish.

Karen was expected to pass over Gulf oil and gas fields from Louisiana to Alabama, but early forecasts suggested the storm would miss the massive oil import facility at Port Fourchon, La., just west of Grand Isle, and the oil refineries that line the Mississippi River south of Baton Rouge.

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Associated Press writers Mark Stevenson in Mexico, Emily Wagster Pettus in Jackson, Miss., and Michael J. Mishak in Miami contributed to this report.