Tropical Storm Debby slowly gained strength Sunday as it hovered in the Gulf of Mexico on a still uncertain path.

The National Hurricane Center, in its 11 a.m. advisory, acknowledged struggling with a “very difficult and highly uncertain forecast.’’

The center shifted the official track significantly from southern Texas to the coast of Louisiana but also cautioned that “we must be ready to make a change of the forecast track at any time.’’

Tropical storm warnings and watches were up for much of the low-lying Louisiana coast, where flooding from storm surge is a serious concern, and for Florida’s Panhandle and Big Bend area.

With the 60 mph storm slowly drifting north, computer models were in sharp disagreement over where it would track west or turn east, picked up by an approaching trough, toward the Big Bend area of Florida.

At 11 a.m., Debby was about 140 miles south-southwest of Apalachicola, and was expected to remain over the open Gulf for the next few days, which forecasters believe could allow it to become a hurricane before making landfall, perhaps sometime Thursday.

For coastal Louisiana, the greatest risk was from storm surge, which forecasters predicted could reach three to five feet. But there was also a risk of flooding from rainfall that could top 10 inches along some sections of the northern Gulf coast.

Though many experts had predicted a normal hurricane season, it has gotten off to a historically fast start. Debby is the earliest fourth storm on record, the center reported, surpassing Hurricane Dennis, which became the fourth storm of 2005 on July 5.