The storm could also produce isolated tornadoes across Florida on Tuesday, the National Hurricane Center said.
As of Tuesday morning, Debby was centered about 90 miles west of Cedar Key, Florida, the weather agency said. The sprawling storm was creeping east at 4 mph, packing maximum sustained winds of 45 mph along the way.
A tropical storm warning is in effect for the Gulf coast of Florida from Mexico Beach to Englewood. The center of Debby will move over northern Florida in the next day or two, the hurricane center said Tuesday.
"Isolated storm total amounts of 25 inches are possible in north Florida," the weather agency said.
In addition to drenching northern Florida, Debby is expected leave an additional 4 to 8 inches of rain across central Florida and far southeastern Georgia as well as 3 to 5 inches in southern Florida and far southeastern South Carolina.
The cyclone has stalled multiple times in the Gulf of Mexico, dumping up to 5 inches of rain per hour on parts of the Florida Panhandle.
Magalie Caragiorgio said Monday that she had been stuck in her home in New Port Richey, near St. Petersburg, since Sunday because of flooding and hasn't been able to get to her job as a nurse.
"It's unnerving because you can't do anything," she said. "I guess I wasn't prepared. I wasn't expecting to be flooded out like this."
The storm already has been blamed for one death in Venus, Florida, about 100 miles southeast of Tampa, when a woman died while trying to shelter her 3-year-old daughter during a tornado Sunday. That twister struck Heather Town's home and flung the 32-year-old about 200 feet into the surrounding woods, the Highlands County Sheriff's Office said Monday.
Neighbors found her still cradling her 3-year-old daughter, who was being treated at a Tampa hospital.
"She never let go of her little one even in death," Highland County Sheriff Susan Benton said.
Another twister hit St. Pete Beach on Sunday night.
Laura Miller wedged herself between her refrigerator and a kitchen pantry as the tornado passed.
"We heard the proverbial noise, the train," Miller said. "The transformer blew, the windows started busting out. It was just very chaotic, all the glass flying, the debris flying into the house. It was pretty intense."
Florida Gov. Rick Scott declared a state of emergency Monday "so we can coordinate the use of all state resources to make sure we can respond promptly if anything happens."
Debby has followed an unpredictable path since forming over the weekend. Storm warnings once stretched as far west as Morgan City, Louisiana, before shifting eastward on Sunday afternoon and Monday. That raised concerns for crews working on 596 manned oil and gas production platforms throughout the Gulf, run by various companies.
Shell, BP and ExxonMobil began evacuating workers from offshore rigs on Sunday, but BP and Shell had made plans to return to those platforms as Debby turned toward Florida.
CNN's Dave Hennen, Sarah Dillingham, Meridith Edwards, Kim Segal and Ashley Hayes contributed to this report.
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