The US Gulf Coast braced Sunday for a hit from Tropical Storm Debby, as it pounded parts of the coast with strong winds and heavy rain, forecasters said.

The Federal Emergency Management Agency urged Gulf Coast residents to be prepared and monitor Debby's progress, amid a tropical storm warning in effect for the Mississippi-Alabama border eastward to the Suwannee River in Florida, as well as for parts of the Louisiana coast.

"History has taught us that storm tracks can change quickly and unexpectedly and people are urged to stay informed and monitor storm conditions," FEMA Administrator Craig Fugate said in a statement.

The Miami-based National Hurricane Center (NHC) said Debby was located about 200 miles (322 kilometers) east-southeast of the mouth of the Mississippi River.

Its top sustained winds had increased to 60 miles (96 kilometers) per hour as the storm moved toward the northeast at five miles (eight kilometers) per hour.

Although the storm's track was uncertain, officials urged Gulf Coast residents across a broad area -- from Texas to Florida -- to remain on alert.

The NHC's official forecast predicted Debby would strengthen to a category one hurricane on the five-point Saffir-Simpson scale before making landfall on Louisiana's coast.

It said tropical storm conditions were already affecting portions of the northeastern Gulf Coast, "making outside preparations difficult or dangerous."

Isolated tornadoes were also possible over portions of the west-central and southwestern Florida peninsula later Sunday.

"The combination of a storm surge and the tide will cause normally dry areas near the coast to be flooded by rising waters," the NHC said, predicting a storm surge of up to three feet (almost a meter) in some areas.

Debby was expected to dump up to 15 inches (38 centimeters) in isolated areas.

"Given the recent heavy rainfall and wet soil conditions, these additional amounts will exacerbate the threat of flooding across portions of northern Florida and southern Alabama," the center warned.