Slow-moving tropical storm Debby's outer bands lashed Florida with rain and kicked up rough surf off Alabama on Sunday, prompting storm warnings for those states and causing at least one death.

The death in Florida was blamed on a tornado spawned by the storm, while a man went missing in the Gulf of Mexico at an Alabama beach.

Coastal Alabama and parts of Florida, including the Panhandle, were under tropical storm warnings. Underscoring the storm's unpredictable nature, forecasters discontinued a tropical storm warning for Louisiana after forecast models indicated Debby wasn't likely to turn west.

Debby already has dumped heavy rain on parts of Florida and spawned some isolated tornadoes, causing damage to homes and knocking down power lines. High winds forced the closure of an interstate bridge that spans Tampa Bay and links St. Petersburg with areas to the southeast. Residents in several counties near the crook of Florida's elbow were urged to leave low-lying neighborhoods because of the threat of flooding.

Debby was essentially stationary about 185 kilometres south-southwest of Apalachicola, Fla., on Sunday evening. While storm tracks are difficult to discern days in advance, a forecast map predicted that the storm would meander north as the week unfolds.

Debby's top sustained winds were at about 95 km/h.

Contradictory computer models

Chris Landsea, a meteorologist at the U.S. National Hurricane Center, said forecasters rely on computer models which were contradictory until Sunday.

"They came into a bit more of an agreement that the westward turn is less likely," he said.

Landsea said every storm is different and has different characteristics, "and in this case it's a very unpredictable storm." He said Debby could become a hurricane.

A major concern will be flooding from heavy rainfall. The storm is moving slowly, allowing its clouds more time to unload rain. A public advisory said parts of northern Florida could receive 25 to 38 centimetres of rain, with some areas getting as much as 25.

The Highlands County Sheriff's Office said in a news release that 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.

"This is quite common with this type of storm," senior hurricane specialist Stacy Stewart with the National Hurricane Center said of the twisters. "They tend to not be very large or long-lived, which can be difficult to detect on radar. So people need to keep an eye on the sky."

Man missing in Alabama

Authorities urged residents to leave low-lying neighborhoods in Franklin, Taylor and Wakulla counties because of flooding. Shelters were open in the area.

In Orange Beach, Ala., a 32-year-old man went missing Sunday in rough surf kicked up by the storm, said Coast Guard Lt. J.G. Torry James. Further information wasn't immediately available.

Near the mouth of the Mississippi southeast of New Orleans, Plaquemines Parish President Billy Nungesser said officials were making preparations to protect the main highway from tidal flooding. Louisiana Gov. Bobby Jindal also declared a state of emergency to make it easier to send supplies and workers to areas that may need it.

However, despite warnings in the Panhandle, Debby hadn't totally dampened vacations.

Thousands were on the beach at Pensacola Beach, Fla., on Sunday morning. Many used their phones to take photos of huge waves crashing into the concrete supports of a fishing pier. There wasn't any rain yet; just gusty winds and dark, fast-moving clouds.

Few people were in the water. Red flags warned tourists to stay out of the surf, and lifeguards cruised the sand on all-terrain vehicles, blowing whistles at anyone who got near the waves.

Workers from rental companies used pickup trucks to gather chairs and umbrellas as a precaution against an unusually high tide.

As of Sunday morning, 23 per cent 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.

National Oceanic and Atmospheric Administration