Forecasters at 2 p.m. put the odds at 80 percent that Tropical Storm Arthur will form from the weather system starting to swirl off Florida's coast. A hurricane hunter airplane is en route to study it.
Forecasters still call for the storm to turn north and pass the Lowcountry offshore on Thursday. At least one forecasting group is calling for heavy rains in the Lowcountry on Thursday and Friday - the start of the July 4th holiday.
Some forecast tracks put the storm near or along the coast as it passes.
The Lowcountry's weather will include chance of showers and thunderstorms throughout the week.
The storm system, which was about 210 miles east of St. Augustine early Monday, had an 80 percent chance of turning into the first tropical cyclone of the season by Friday, according to the National Hurricane Center.
The instability over the Atlantic Ocean will put the Charleston area's chance of rain around 20 percent early in the week. The risk will increase to about 40 percent by Thursday.
Here is the complete forecast, according to the National Weather Service station for Charleston:
Monday: A slight chance of showers and thunderstorms after 2 p.m. Sunny, with a high near 91. East wind 7 to 10 mph. Chance of precipitation is 20 percent.
Monday night: Partly cloudy, with a low around 74. Southeast wind 5 to 10 mph becoming light after midnight.
Tuesday: A slight chance of showers and thunderstorms after 2 p.m. Mostly sunny, with a high near 90. East wind 5 to 8 mph. Chance of precipitation is 20 percent.
Tuesday night: Partly cloudy, with a low around 77. Southeast wind 5 to 9 mph.
Wednesday: A chance of showers and thunderstorms. Mostly sunny, with a high near 90. Light southeast wind increasing to 5 to 10 mph in the morning. Chance of precipitation is 30 percent.
Wednesday night: A chance of showers and thunderstorms. Mostly cloudy, with a low around 77. Chance of precipitation is 30 percent.