The slowly weakening storm was moving toward land at around 7 miles an hour, and was 235 miles southwest of the mouth of the Mississippi River. It is expected to slow considerably before making a right turn toward the Alabama and Florida coastline, but it is likely first to pass across the southeastern tip of Louisiana sometime on Saturday evening. Heavy rainfall is expected all along the coast, with as much as 10 inches in some isolated areas.
The storm is currently not expected to reach hurricane strength, but officials with the National Hurricane Center insisted, as they do every year, that residents in its path should not dwell too much on storm categories or rely too strictly on the black line that delineates a storm's predicted trajectory.
"We want to stress there's hardly any significant difference in impacts between a strong tropical storm and one that reaches the hurricane threshold," said Dennis Feltgen, a spokesman who, unlike his colleagues at the hurricane center, had been on furlough.
Mr. Feltgen emphasized that a three-to-five-foot storm surge is possible all the way from the mouth of the Mississippi River to Mobile Bay in Alabama, and that a one-to-two-foot surge might occur all the way from Louisiana to Tampa, Fla.
The storm is putting hundreds into action who were otherwise waiting for Congress to sort things out. While the National Hurricane Center remained almost fully staffed despite the shutdown, teams of federal liaisons with the Federal Emergency Management Agency have been called out of furlough, as have some Congressional staff members.
"We will not let the government shutdown in Washington in any way hurt our emergency response efforts in Florida," said Gov. Rick Scott in a statement.
In Louisiana, Gov. Bobby Jindal declared a state of emergency, and 650 National Guard members were mobilized, including 520 who had been on furlough.
The mayor of Grand Isle, La., one of the state's few beachfront communities and a frequent inaugural stop for gulf storms, called for a mandatory evacuation because of concerns that the island would be cut off. Mandatory evacuations have been ordered in some other parts of southern Louisiana as well, including Plaquemines Parish, which suffered from devastating floods during Hurricane Isaac last year.
"We almost made it through the entire hurricane season without having a threat like this," Mayor Mitchell J. Landrieu of New Orleans said at a news conference. "But it is what it is, and we've been through this before." The city is expecting heavy rain but no severe impacts.
Gov. Phil Bryant of Mississippi also declared a state of emergency, and state officials are warning that the soil along the coast, already rain soaked, could cause some problems.
"The ground is a little bit wet and weak, so trees may come down," said Brent Carr, a spokesman for the Mississippi Emergency Management Agency. "People need to be prepared for possibly a few days with no power."
The storm has provoked little anxiety, and many state emergency officials are simply encouraging people along the coast to make their own preparations. At least one high school football game and a Kiwanis pancake breakfast have been rescheduled, while a motorcycle rally was still going ahead at Panama City Beach, Fla., and the polka bands are still on call for the Oktoberfest celebration at the Flora-Bama Lounge.
Once the storm makes landfall, it is expected to head up through Georgia and the Carolinas, raising the prospect of flooding and tornadoes.
And after that, Mr. Feltgen said, "if Congress hasn't settled this issue, I'll probably go back on furlough."
