At 10 p.m. ET, tropical storm Andrea was about 430 kilometres southwest of Tampa and moving north at about nine km/h. The storm had maximum sustained winds near 65 km/h, with higher gusts.
Forecasters said tropical storm conditions "are expected to first reach the coast within the warning area by Thursday afternoon."
The storm is then expected to move over southeastern Georgia and eastern South Carolina Thursday night and into Friday, the storm centre said.
Andrea is the first named tropical storm of what is predicted to be a busy 2013 Atlantic hurricane season.
The Canadian Hurricane Centre said in a statement the storm is expected to transform "into a wet low pressure system affecting Atlantic Canada this weekend."