Gulf Coast residents kept a watchful eye and the oil industry began making preparations Thursday as forecasters warned that a weather system swirling over waters west of Florida could make landfall as a tropical storm over the weekend.

In storm-skittish Louisiana, the governor declared a state of emergency late in the day, putting the National Guard on alert and school buses, ambulances and evacuation shelter workers on standby.

Conditions favor the low-pressure system becoming a subtropical or tropical cyclone within the next day, the National Hurricane Center said. A coastal flood watch is in effect through Saturday, the National Weather Service said.

The storm's path remains uncertain, but "the general consensus" is that it will hit between the mouth of the Mississippi River and Alabama's Mobile Bay, said Sam Shamburger, a Weather Service meteorologist. That's about the same route Hurricane Katrina took in 2005.

The system could make landfall early Saturday, said Mark Smith, a spokesman for the Louisiana Office of Homeland Security and Emergency Preparedness.

"With Louisiana still suffering from the ravages of Katrina and having so many residents living in travel trailers and mobile homes, we feel it's prudent — at this time — less than 36 hours out from the onset of landfall, to recommend the governor make the declaration," Smith said.

A tropical storm carries sustained winds of 39 to 73 mph. In comparison, Katrina, which killed hundreds of people and flooded most of New Orleans, made landfall as a Category 3 storm, with sustained winds of at least 111 mph.

Oil industry workers have left five production platforms in the Gulf, and three drilling rigs have been evacuated, according to the federal Minerals Management Service.

In Louisiana, officials were taking no chances. Gov. Kathleen Blanco, in Spain on an economic development trip, ordered the state's Emergency Operations Center to open, and personnel will closely monitor the weather.

"From a planning and practical standpoint, we have to plan for a level higher than it is to ensure that we have the assets and resources in place should it become more severe," Smith said.

In New Orleans, which took the brunt of Katrina's fury and is still vulnerable to flooding, officials urged residents who might need help in the event of an evacuation to register with the city's 311 service.

"Now is the time to do so," said Col. Jerry Sneed, emergency office director.

Authorities encouraged residents to clear leaves from storm drains and catch basins on or near their properties to limit flooding in the event of heavy rains.

In Mississippi's coastal Hancock County, officials handed out sandbags Thursday, said Brian Adam, director of the county emergency management agency.

A telephone message recorded by Mississippi Gov. Haley Barbour warned residents not to panic but to be prepared. It started going Wednesday night, primarily in parts of Mississippi slammed by Katrina.