(CNN) - He used sand bags and a water pump, but Chad Mercer couldn't stop floodwaters from rising to his knees inside his Starke, Florida, home.
"I'm laughing about it now, because I've been doing this since 6 this morning," he told CNN affiliate WJXT Monday night. "Gotta laugh now."
But Tropical Storm Debby proved to be no laughing matter as it wreaked widespread havoc in Florida. The slow-moving storm has killed one person, dumped nearly 2 feet of rain in some areas and triggered flooding resulting in evacuations, rescues and road and interstate closures.
And Debby isn't finished -- forecasters warned the storm could bring another 8 inches of rain to the northern part of the state as it slogs through, headed from the Gulf of Mexico to the Atlantic Ocean. Isolated areas could see a total of 25 inches of rain from Debby.
In Columbia County, west of Jacksonville, authorities were preparing for the Suwannee River to rise 22 feet in one day.
The river was 55 feet at White Springs, Florida, on Monday, said Harvey Campbell, spokesman for Columbia County emergency operations. On Tuesday, the prediction is for the river to rise past flood stage -- 77 feet.
"We have significant flooding problems," Campbell said. "I have people who don't remember in their lifetime the kind of rain we had overnight."
Most of those living along the river have flat boats and "don't want to be rescued," he said. The area is anticipating another 5 to 8 inches of rain on Tuesday, he said, and "snakes are on the move."
President Barack Obama called Florida Gov. Rick Scott on Tuesday "to ensure the state had no unmet needs as the governor and his team continue to respond to extreme weather and flooding," the White House said.
Portions of Interstate 10 in Baker County in northeastern Florida were closed Tuesday in both directions because of standing water, according to the Florida Highway Patrol, which posted a lengthy list of water-related road closures on its website.
More than 20 inches of rain have fallen across northern Florida, particularly in areas just south of Tallahassee, according to the National Weather Service. Panacea, Florida, saw 20.63 inches in 24 hours; Sanborn, Florida, received 16.26 inches; and Saint Marks, Florida, received 20.96 inches over the past 48 hours, according to the weather agency.
The National Weather Service in Tallahassee issued a civil emergency message telling residents to stay home and off the roads.
In Sopchoppy, Florida, authorities rescued 38 people from homes surrounded by rising water overnight, said Keith Blackmar of the Wakulla County Sheriff's Office.
"It's astonishing. I've never seen anything like this," Blackmar said. "Our soil is sandy, so it handles water well, but not this much rain."
Flooding was seen as far south as Fort Myers, Florida, where the Caloosahatchee River overflowed its banks into the downtown area. CNN iReporter Alex Butler, who is also a reporter at CNN affiliate WFTX, said normally there is a wall separating the land from the river, but the wall was underwater Tuesday.
As of 11 a.m. ET Tuesday, Debby was centered about 70 miles west of Cedar Key, Florida, the National Hurricane Center said. The sprawling storm was creeping east at 3 mph. Its winds had weakened slightly, from 45 to 40 mph, and Debby was expected to be downgraded to a tropical depression over the next day or two, forecasters said.
The widespread damage resulted not only from Debby's slow movement, but also from the storm's size -- tropical storm-force winds of at least 39 mph extended outward up to 205 miles from its center. On Monday, rain bands from Debby passed over Hilton Head Island, South Carolina.
The storm also dumped 5 inches of rain hourly in some Florida Panhandle locations as it stalled in the Gulf earlier this week. In Clay County, authorities were urging residents near Black Creek to voluntarily evacuate, as the creek was more than 5 feet above flood stage, according to WJXT.
"This could really break some records, unfortunately," Bernita Bush of Clay County Fire and Rescue told the station Tuesday.
Shelters were open in numerous locations for residents across the state.
A tropical storm warning is in effect for the Gulf coast of Florida from Mexico Beach to Englewood. The storm spawned at least seven tornadoes in central Florida on Sunday, the National Weather Service said, including one that killed a woman.
Heather Town, 32, of Venus, Florida, about 100 miles southeast of Tampa, died while trying to shelter her 3-year-old daughter during a twister, authorities said. The tornado struck her home and flung Town about 200 feet into surrounding woods, the Highland County Sheriff's Office said Monday.
She was found still cradling her child, 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 tornado struck St. Pete Beach Sunday night.
"We heard the proverbial noise, the train," resident Laura Miller said. "The