Updated at 10:13 p.m. ET: Parts of Florida and Alabama were under a tropical storm warning Sunday as Debby churned off the Gulf Coast, leaving wary residents to closely watch a storm whose path has so far been difficult to forecast.
Underscoring the storm's unpredictable nature, forecasters discontinued a tropical storm warning for Louisiana after forecast models indicated Debby was less likely to make a westward turn than initially predicted. Coastal Alabama and parts of Florida, including the Panhandle, remained under tropical storm warnings.
Debby already had dumped heavy rain on parts of Florida and spawned some isolated tornadoes, causing some 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.
Debby, no longer expected to gain hurricane strength, packed winds of 60 mph, the Miami-based center said.
Citing a "significant change in the forecast track," the NHC said Debby is expected to hit the Florida Panhandle near Panama City on Thursday as a tropical storm. "This forecast remains uncertain due to weak steering currents," the NHC said.
The NHC had previously predicted that the storm would track westward toward the Louisiana coast as a weak hurricane, spurring Louisiana Governor Bobby Jindal to declare a state of emergency.
Chris Landsea, a meteorologist at the 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 was could become a hurricane.
A major concern will be flooding from heavy rainfall. Parts of Florida and southeast Georgia could receive 10 to 15 inches of rain, with some areas getting as much as 20, he said.
Debby's top sustained winds were at about 60 mph (95 kph). The storm was moving toward the northeast at 3 mph (6 kph).
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.
At least one tornado linked to the storm touched down Saturday in southwest Florida, but no injuries were reported. Another was reported Sunday in Venice, damaging some homes.
"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."
Debby has shut nearly a quarter of offshore crude oil and natural gas production, the U.S. government said.
BP Plc, the largest oil producer in the Gulf of Mexico, shut in all of its production. The Louisiana Offshore Oil Port, the only U.S. port for handling the largest oil tank ships, stopped operating due to rough seas.
ConocoPhillips and Royal Dutch Shell Plc had also shut some of their production as of Sunday as the first storm of the 2012 Atlantic hurricane season to threaten offshore production gained strength in the Gulf.
The storm has a 30 percent chance of reaching hurricane strength before landfall and could temporarily disrupt 55 percent of Gulf offshore oil production and 44 percent of natural gas production due to short-term evacuations, according to Weather Insight, a unit of Thomson Reuters.
Despite storm 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 with rental companies used pickup trucks to gather chairs and umbrellas as a precaution against an unusually high tide.
The Associated Press and Reuters contributed to this story.
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