Tropical Storm Lee was already pushing rain into south Mississippi and Louisiana, and officials said it could bring major flooding over the next few days.
Barbour's state of emergency frees up resources that can be used to prepare for the storm. The declaration was for the following counties: George, Hancock, Harrison, Jackson, Marion, Pearl River and Stone. The counties are all on or near the coast.
"While it is not a hurricane, this weather system is expected to cause tremendous flooding. Make preparations now to protect your family and your property," Barbour said in a news release.
Jackson County Emergency Management Director Donald Langham said county officials also declared a state of emergency Friday. Jackson County is one of Mississippi's three coastal counties and borders Alabama. It is home to Ingalls Shipyard, Mississippi's largest private employer.
"The main concern is because it is such a slow moving storm it's going to be dropping a tremendous amount of rain in the next few days," Langham said Friday. "The outer bands are starting to come ashore. Some of it's heavy, some of it's light, but it will be picking up."
Mississippi Emergency Management Agency spokesman Jeff Rent said MEMA is having ongoing discussions with officials in the state's southernmost counties about what preparations they're making and "how we can support them through this."
Rent said the main concern is water, with 17 to 20 inches of rain possible in some areas. Coastal flooding is another concern due to an expected rise in tides of up to four feet. Wind could also uproot trees in soggy soil and knock out power.
MEMA plans to send sandbags to Hattiesburg, a halfway point between Jackson and the coast. Officials from south Mississippi can pick up the bags there.
"There's going to be some wind. You have all the typical things that come with a tropical system — torrential rain, some wind, there could be some spinoff tornados," Rent said.
"When you have rain over several days, it doesn't take much wind to knock down trees. So there will be some power outages," Rent said. "We're concerned about all the effects, but what concerns us the most is the rainfall. It will be wave after wave of showers and storms."
Forecasters upgraded the storm Friday from a depression to a tropical storm. Tropical Storm Lee became the 12th named storm of the Atlantic hurricane season. Around midday Friday, the center of the storm was nearly stationary off the Louisiana coast. Its center was expected to make landfall in Louisiana over the weekend.
A tropical storm warning was in effect for coastal Mississippi. That warning extends from Pascagoula to Sabine Pass, Texas.
While officials are keeping a close watch on the tropical depression in the Gulf of Mexico, so far it has not caused a lot of concern for tourism, said Taryn Sammons, spokeswoman for the Mississippi Gulf Coast Convention and Visitors Bureau.
"As far as I know everything is still going on as planned. I haven't heard of any cancelations," Sammons said.
Sammons said the Mississippi Gulf Coast markets many indoor activities that wouldn't be hampered by rainy weather, such as casinos, museums and restaurants.