Tropical Storm Debby churned in the Gulf of Mexico on Sunday, inching closer to the northern rim of the region. Forecasters are still uncertain of the storm’s path, and authorities warned of flood possibilities from Florida to Texas. As of 5 a.m. Sunday, Debby was about 165 miles southeast of the Mississippi River and was moving north at three miles per hour. At least one tornado linked to the storm touched down Saturday in southwest Florida, and heavy squalls pounded the state. Forecasters said Debby could near hurricane strength by Monday night.