MIAMI - Tropical Storm Hanna on Monday developed into a full-fledged hurricane east of the Bahamas in the Atlantic ocean, US officials reported, as deadly Hurricane Gustav pounded the Gulf Coast near New Orleans.

"Hanna becomes the fourth hurricane of the season," the National Hurricane Center reported in a bulletin, adding that the storm was very near Mayaguana Island in the southeastern Bahamas and packing winds near 75 miles (120 kilometers) per hour.

The NHC said hurricane warnings were issued for the Central Bahamas, Southeastern Bahamas and Turks and Caicos Islands, and that Hanna was churning west-southwest at five miles (seven kilometers) per hour, but was expected to turn northward in a direction of the southeaster US coast.

"Some additional strengthening is forecast during the next 24 hours" as it moves over the Bahamas -- notably Eleuthera and Abaco islands -- and produces up to 12 inches (25 centimeters) of rain through Thursday, it said.

By Friday it is projected to threaten the US coastline near near the Georgia-South Carolina border, giving the United States a second major cyclone to contend with in the same week.

On the Gulf of Mexico's US coast, ferocious rain and wind gusts unleashed by Hurricane Gustav threatened to send surge waters flooding into New Orleans three years after Katrina decimated the Louisiana city.

Also taking shape in the Atlantic Monday was Tropical Depression Nine, which formed about 1,470 miles (2,365 kilometers) east of the Leeward Islands, and was expected to travel slowly in a west-northwest direction.