The storm is 605 miles (975 kilometres) east of Antigua and moving quickly westward, the National Hurricane Center said yesterday.
With maximum sustained winds of 40 miles per hour (65 kilometres per hour), it has sparked storm watches on several islands, including Antigua, Montserrat and Barbuda.
A tropical storm watch indicates that tropical storm conditions are possible within 48 hours.
"On the forecast track, the centre of Erika will be near the Leeward Islands Wednesday night and early Thursday," the Miami-based centre said.
On its current path, Erika - expected to strengthen over the coming days - could reach the Bahamas as a hurricane over the weekend, according to the NHC.
Erika comes on the heels of Danny, the first hurricane of the Atlantic season, which dissipated Monday as it reached the Caribbean.
