The storm lost its tropical characteristics late Wednesday and was downgraded to a post-tropical cyclone, with maximum sustained winds of 40 mph, the National Weather Service said. No further public advisories were going to be issued, the service said.
The Polk County death was a 21-year-old woman whose vehicle hydroplaned and crashed, said Jessica Sims, spokeswoman for the emergency team.
In Pinellas County, Armando Perez, 71, was found face down in floodwater outside his Indian Rocks home, county officials said. An autopsy determined the cause of death to be drowning, with heart disease as a contributory factor, authorities said.
"According to detectives working with the medical examiner's office, Mr. Perez may have suffered a heart attack serious enough to incapacitate him, so that he collapsed and could not remove himself from the floodwaters," the Pinellas County Sheriff's Office said in a statement.
The death in Highlands County came when a tornado struck the town of Venus, Florida, about 100 miles southeast of Tampa.
Heather Town, 32, died while trying to shelter her 3-year-old daughter, officials said. The twister flung her nearly 300 feet into surrounding woods, the state emergency response team said. She was found still cradling her child, who was being treated at a hospital Sunday, officials said.
The State Emergency Response Team initially said three people had died, then briefly decreased the total to two before reconfirming the Pinellas County man's death was storm-related, Sims said.
Authorities did not release details of the death in Lake County, beyond confirming that one life had been lost.
In Alabama, the search continued Wednesday for a 32-year-old man who went missing Sunday while swimming off the coast of Orange Beach, according to Battalion Chief Kevin Lanford of Orange Beach Fire-Rescue.
On Wednesday, authorities in Florida's Pasco County lifted an evacuation order for flooded residents and businesses between the Anclote and Pithlachascotee Rivers, officials said.
More than 7,000 residential and commercial addresses, which were evacuated, were hit by flooding waters, and power had been restored to about 1,800 of the homes, authorities said.
Seventy-three county residents stayed in shelters Tuesday night, county spokesman Eric Keaton said Wednesday. Pasco County is north of Tampa.
Debby made landfall as a tropical storm on Florida's northern Gulf Coast Tuesday and weakened while crossing the northern portion of the state.
Rain had finally moved out of the region Wednesday, according to National Weather Service radar, but flood warnings remained in effect across northern Florida. All tropical weather watches and warnings were canceled.
"Rainfall associated with Debby will continue to diminish across the Florida peninsula today," forecasters said. "Additional isolated rainfall amounts of up to 1 inch will be possible in some of the lingering rain bands, mainly over southern Florida."
In Venice, Florida, about 60 miles south of St. Petersburg, CNN iReporter Bob Wilder sent pictures of heavy surf.
"The rain has pretty much slowed down, though we did have a pretty heavy squall pass over the house a few minutes ago," he said. "This storm has been different in that it has hung around for so long. Normally, we'll have a day of heavy weather and that's it. Two or three days of on-again, off-again rain and constant wind is a bit unusual."