National Hurricane Center
Heavy rains in south Alabama and the Florida Panhandle are expected to flood waterways, potentially submerging bridges and flooding homes.
It was the second hurricane to hit the Gulf Coast in less than three weeks and the latest blow in one of the busiest hurricane seasons ever recorded.
The Category 1 storm may also dump up to 2 feet of rain on the region and spawn tornadoes.
Forecasters say Tropical Storm Sally is expected to become a hurricane on Monday and reach shore by early Tuesday.
Officials in the New Orleans area issued a mandatory evacuation order for areas outside of levee protection.
Forecasts suggest the storm would reach hurricane strength early in the week before striking the northern Gulf Coast.
The National Hurricane Center projected that Laura will become a Category 3 hurricane before landfall late Wednesday or early Thursday.
The Gulf Coast braced for a history-making onslaught from the twin storms, with many evacuees recalling the damage caused by Hurricane Katrina in 2005.
The storm grew into a Category 1 hurricane early Friday as the Bahamian government urged citizens to prepare for the worst.
The storm is expected to keep inundating the northern Gulf Coast well into Monday.