Forecasters said radar spotted possible tornadoes spun off by the storm overnight in southern Alabama and the Florida panhandle, and more are possible on Wednesday night in MS and western Alabama.
Gordon could drop heavy rain - generally 4 to 8 inches, but as many as 12 - from Florida's western panhandle to southern Arkansas through Thursday, the National Hurricane Center said.
Governors in Alabama, Mississippi and Louisiana all declared states of emergency to better mobilise state resources and National Guard troops for the storm.
A child has been killed in Florida after a tree was blown on top of his mobile home in an incident which may be linked to Gordon.
Gordon will bring some much needed rain to parts of our area today.
A couple of tornadoes are possible near the Alabama and Florida coasts, the NHC said.
In coastal Mississippi's Jackson County, people filled bags with sand at government distribution points, intending to line their homes with them to avert flooding. Officials haven't released the child's identity.
Separately, the NHC on Wednesday named storm Florence, which was about 1,370 miles (2,205 km) east-southeast of Bermuda, as the first major hurricane of the 2018 Atlantic hurricane season with winds of 125 miles per hour (201 kph).
Smith said there's more to it than rain and flooding; it's also the unsafe rip currents and possible power outages.
Driftwood and other debris on the causeway made for hazardous driving early Wednesday to nearby Dauphin Island, where streets were submerged in seawater overnight.
The system will likely march west-northwest over the next five days, at which point forecast models are split on where it will go. At 10:52 Eastern Standard Time, a tornado was confirmed over Galt City, Florida, near Milton, moving northwest at 35 miles per hour. The mayor noted the ongoing construction on Highway 1, the lone road that connects Grand Isle to the rest of the state, and said it could cause "severe problems" for people evacuating.
Even though Gordon has been downgraded to a tropical depression, he's still packing quite a punch, along with the potential for life-threatening storm surges. No one else inside the home was injured, spokeswoman Amber Southard said.
More than 35,000 homes and businesses in Alabama and MS were without electricity early yesterday, Poweroutage.us reported.
United States oil producer Anadarko Petroleum Corp evacuated workers and shut production at two offshore platforms on Monday, and other companies with production and refining operations along the Gulf Coast said they were securing facilities.
Anadarko also said it plans to begin moving workers back to two offshore sites and will restart production as quickly as possible.