Tropical Storm Hanna threatens Gulf Coast

Satellite image of Tropical Depression 9 taken Thursday at 10:02 p.m. EDT.

MIAMI, Florida (CNN) -- A tropical depression churning over the central Gulf of Mexico strengthened Friday morning and became Tropical Storm Hanna, the season's eighth named storm.

The National Weather Service issued a tropical storm warning from Grand Isle, Louisiana, to Apalachicola, Florida. A tropical storm warning means that tropical storm conditions are expected within the next 24 hours.

Hanna is expected to turn to the north later today, the Weather Service said. The center of the storm is expected to reach the coast within the warning area sometime Saturday morning.

A tropical storm watch remains in effect from east of Apalachicola to the Suwanee River in Florida.

Hanna's maximum sustained winds are near 45 mph with higher gusts. Additional strengthening is forecast during the next 24 hours, although Hanna is not expected to reach hurricane intensity prior to landfall.

At 4 a.m. CDT Friday, the center of the storm was 255 miles south-southwest of Pensacola, Florida. It was moving toward the northwest at about 8 mph.

Rainfall accumulations of 4 to 8 inches, with isolated higher amounts, can be expected near the path of Hanna, the Weather Service said. Large waves and dangerous rip currents will gradually increase across the watch and warning area on Friday.

Isolated tornadoes are possible, forecasters said, mainly to the east of where the center of Hanna makes landfall.

The first six storms of the Atlantic season all reached tropical storm strength but fell short of hurricane force 74 mph winds. But the seventh storm, Gustav, barreled offshore from the Atlantic seaboard and reached hurricane status near the Canadian east coast, far from its tropical origins.

Gustav spread heavy rain and high winds over Nova Scotia, Prince Edward Island and Newfoundland before heading off to the Labrador Sea, where it lost its hurricane status but remained a very large and strong extratropical storm.

Earlier this week, as a tropical storm, Gustav tormented North Carolina's Outer Banks.