CHARLESTON, S.C. -- A storm off the Southeast coast that sent bands of rain into Georgia and South Carolina developed into a tropical depression late Friday night, the National Hurricane Center said.

The hurricane center issued a tropical storm warning from South Santee River, S.C., to Cape Hatteras, N.C., including Pamlico Sound. That means tropical storm conditions are expected within the warning area within the next 24 hours.

A tropical storm watch was issued from north of Edisto Beach, S.C., to South Santee River, and from north of Cape Hatteras to Oregon Inlet, meaning tropical storm conditions are possible within the watch area, generally within 36 hours.

At 11 p.m., the center of the tropical depression about 65 miles south-southeast of Charleston and about 330 miles southwest of Cape Hatteras. Movement was to the northeast at about 6 mph, and the hurricane center expected the storm to continue that movement for the next two days, keeping the storm close to the North and South Carolina coasts.

Maximum sustained winds were near 30 mph with higher gusts. Forecasters called for some strengthening in the next 24 hours, and said the depression could become a tropical storm on Saturday.

Meteorologist Jonathan Lamb of the National Weather Service in Charleston said most of the rain remained offshore and, even if the storm deepened, it would not cause too many problems.

"Even if it did develop and stayed off the coast, the impacts on the Charleston and Savannah areas would be relatively low," he said. "It wouldn't be anything near a hurricane or anything like that."

He said the storm could bring occasional showers and thundershowers, some heavy at times.

A tropical depression has winds of 38 mph or less. It becomes a tropical storm with winds sustained at 39 mph.

If the system develops into a tropical storm, it would be named Cristobal, the third named in the 2008 Atlantic Hurricane season