The governor declared a statewide emergency, and a tropical storm warning was in effect for most of Florida's Gulf coast. At least one person was killed by a twister in Florida, and crews in Alabama searched for a man who disappeared in rough surf Sunday.
In St. Pete Beach on Florida's Gulf coast, a tornado ripped the roof off a marina and an apartment complex, and felled fences, trees and signs.
Kourosh Bakhtiarian's yard was flooded. He said people were driving around to survey the area, and he was upset police hadn't closed off the neighborhood streets.
"We have a lot of visitors from outside of this area. They just want to see exactly where the disaster is. I mean, this is not the happiest time. Usually people come to the beach when it's sunny and nice and they can go to get a tan. But today, we saw a lot of visitors here."
State officials estimated at least 35,000 homes and businesses were without power, including Bakhtiarian's home.
The storm closed the sole bridge to St. George Island, a popular vacation island in Florida. Power was already out on the island and authorities said it could be for days.
"The tourists cleared out. It's not a good thing and hurts the economy during a week in peak season," said Patrick Sparks, 26, a manager at Eddy Teach's bar. "It's a tropical storm - it's not even a category one (hurricane). It's a little rash to send everyone home."
Residents in several counties near the crook of Florida's elbow were urged to leave low-lying neighborhoods because of the threat of flooding. Shelters were opened in some areas.
High winds forced the closure of an interstate bridge that spans Tampa Bay and links St. Petersburg with areas to the southeast. In several locations, homes and businesses were damaged by high winds authorities believe were from tornadoes.
The constant barrage of wind and rain triggered fears of the widespread flooding that occurred across the Florida Panhandle during Hurricane Dennis in 2005.
Debby's center was essentially stationary about 50 miles (80 kilometers) south of Apalachicola. Debby's top sustained winds were around 45 mph (72 kph) with little change in strength expected over the next day or so. The forecast map indicated the storm would crawl northeast, eventually coming ashore in Florida later this week. However, a storm's path is difficult to discern days in advance.
Underscoring the unpredictable nature of tropical storms, forecasters at one point thought Debby would head west toward Texas.
"There are always going to be errors in making predictions. There is never going to be a perfect forecast," said Chris Landsea, a meteorologist at the National Hurricane Center.
The storm is moving slowly, allowing its clouds more time to unload rain. A public advisory said parts of northern Florida could get 10 to 15 inches of rain, with some areas getting as much as 25 inches.
The Highlands County Sheriff's Office said several tornadoes moved through the area southeast of Tampa, damaging homes.
Sheriff's office spokeswoman Nell Hays said a woman was found dead in a house in Venus that was destroyed in the storm. A child found in the same house was taken to the hospital.
No further information was available on the child's condition or either person's age.
In Orange Beach, Ala., fire and rescue workers searched for a South Carolina man who was vacationing with his family when he went under. His name and hometown were not immediately released.
As of Sunday, 23 percent of oil and gas production in the region had been suspended, according to a government hurricane response team. Employees have been evacuated from 13 drilling rigs and 61 production platforms in the Gulf of Mexico.
The storm was not expected to result in higher oil and gas prices.
"It's largely a non-event for oil," said Tom Kloza, chief oil analyst at the Oil Price Information Service.