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(CNN) — The tropical disturbance that brought holiday weekend flooding to Florida is now Bertha — the second named tropical system of the year.

As it moved off the Florida coast, the system gained energy from the warm ocean water.

It organized quickly overnight and has sustained winds of 45 mph, with higher gusts. The center is located around 30 miles east-southeast of Charleston and is moving northwest toward the coast. Bertha will make landfall in the Carolinas later Wednesday as a tropical storm.

“The center of the circulation at 8 a.m. ET is a little over 30 miles offshore and is closing in fast,” CNN meteorologist Chad Myers said. “There will only be a small window of opportunity for more strengthening, but it is very warm water now it is certainly possible.”

The system has become “significantly better organized,” said the National Hurricane Center. Tropical storm-force winds have already been reported from a buoy within the storm.

The NHC issued a tropical storm warning for the coast of South Carolina from Edisto Beach to South Santee River.

“The center of Bertha will move onshore in the warning area in the next

few hours and then move inland across eastern and northern South Carolina later today and into west-central North Carolina by

tonight,” the NHC said.

The storm will cause flash flooding over portions of the Carolinas and very gusty winds.

Life-threatening surf and rip currents will be likely along the coasts of Georgia and the Carolinas throughout the day.