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NEW ORLEANS (CBSNews.com)-Though weakening slightly, Tropical Storm Karen remained poised to become the first named storm to hit the U.S. during what had been a relatively quiet hurricane season.

Karen was forecast to lash the northern Gulf Coast over the weekend as a weak hurricane or tropical storm. Officials on the Louisiana barrier island of Grand Isle called for a mandatory evacuation.

A hurricane watch from Grand Isle to west of Destin, Fla., was downgraded to a tropical storm watch. 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.

CBS News hurricane consultant David Bernard reports Karen had slowed down Friday and was not expected to cross the coastline until late Sunday or early Monday morning. A powerful cold front causing a historic October blizzard in the Northern Plains will eventually then scoop up the storm.

TheNational Hurricane Centerin Miami said late Friday that Karen was about 235 miles south-southwest of the mouth of the Mississippi River and 270 miles south-southeast of Morgan City, La. It's moving north-northwest at 7 mph. Maximum sustained winds were 50 mph.

Along with strong winds, the storm was expected to produce rainfall of 3 to 6 inches through Sunday night, with isolated totals up to 10 inches possible. Forecast tracks showed it possibly brushing, or crossing, the southeast Louisiana coast before veering eastward toward south Alabama and the Florida panhandle.

Lifeguard stands were moved off the beach to higher ground on beaches in Florida and Alabama. States of emergency were in effect in Alabama, Louisiana, Mississippi and parts of Florida.

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

In Mississippi, Gov. Phil Bryant urged 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.

Florida Gov. Rick Scott declared an emergency for 18 counties.

Traffic at the mouth of the Mississippi River was stopped Friday morning in advance of the storm.

In New Orleans, CBS affiliate WWL-TV reports some inmates housed at Orleans Parish Prisonwere being moved ahead of the storm.

Orleans Parish Sheriff's Office spokesman Philip Stelly told the station that 432 inmates, 298 male and 134 female, who are housed in tents were being moved as a precaution to an undisclosed location.

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 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 thatstalled 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 tothe government shutdownto prepare for the storm.

White House spokesman Jay Carney said President Obama was being updated about the storm. He said Mr. 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.

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 were expected to be largely the same: Heavy rain with the potential for similar storm surge.

Camardelle, whose vulnerable island is often the first to order an evacuation in the face of a tropical weather system, said the town was 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.

© 2013 CBS Interactive Inc. All Rights Reserved. This material may not be published, broadcast, rewritten, or redistributed. The Associated Press contributed to this report.

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