Preparations began Thursday along the central Gulf Coast and local emergency officials were among those on alert as recently formed Tropical Storm Karen threatened to become the first named tropical system to menace the United States this year.

Hurricane and tropical storm watches were posted from southeast Louisiana to Florida and some oil and gas platforms in the storm’s projected path were being secured and evacuated.

The National Hurricane Center in Miami said Karen was about 485 miles south of the mouth of the Mississippi River and had maximum sustained winds of 65 mph.

The hurricane watch was in effect from Grand Isle to Indian Pass in the Florida Panhandle. A tropical storm watch also was in effect for parts of the Louisiana coast west of Grand Isle, including the New Orleans area.

Karen was moving north-northwest at 12 mph. It could be at or near hurricane strength by Friday, forecasters said.

On Thursday morning, the National Hurricane Center gave the system a 70 percent chance of development within 48 hours.

The Washington Parish Office of Homeland Security and Emergency Preparedness urged local residents to stay alert.

“We are currently in the cone of error, so we ask all to remain vigilant and stay tuned to local media,” said Emergency Management Specialist Bobbi Jo Breland. “Our Facebook and parish government web page will be updated as information on this system is received.”

After the 2 p.m. briefing, Breland said the forecast track had not changed.

“With the current track we could possibly experience 2 to 4 inches of rain, and wind speeds of 15 to 25 miles per hour with the possibility of tropical storm-force gusts,” she said.

At 2:30 p.m. Gov. Bobby Jindal declared a state of emergency based on the forecast.

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 a weak hurricane or strong tropical storm, Karen’s effects are expected to be largely the same: heavy rain and the potential for similar storm surge.

(The Associated Press contributed to this article.)