Tropical storm warnings were posted Thursday from Texas to Mississippi as Tropical Depression 13 formed in the Gulf of Mexico.
The depression was forecast to grow into a tropical storm that could bring up to 10 to 15 inches of rain over southern Louisiana, Mississippi and Alabama through Sunday, the National Hurricane Center said. The storm would be named Lee.
Louisiana Gov. Bobby Jindal declared a state of emergency, which allows him to activate the National Guard.
Early forecasts were for landfall early Saturday afternoon in south-central Louisiana, but National Weather Service meteorologist Frank Revitte said it was too early for a firm time or location.
"Wow. This could be a very heavy, prolific rainmaker," Revitte said.
According to the hurricane center, maximum sustained winds could reach 60 mph by Saturday, lower than hurricane strength of 74 mph.
Meanwhile, Tropical Storm Katia continued to spin through the Atlantic toward the United States. Though some models predict the storm will curl north, others anticipate a more linear track toward Florida. Forecasters said it is too early to predict whether Katia will strike the United States.
Katia was downgraded from a hurricane to a tropical storm Thursday, but it was over warm waters and in a low wind shear environment, two factors that could propel it back to hurricane status.
A third patch of weather 360 miles north of Bermuda also got the attention of forecasters Thursday, though it was expected to harmlessly shove off to the northeast.
Information from the Associated Press was used in this report.