Subtropical Storm Theta formed Monday night making this the most active Atlantic hurricane season on record with 29 storms so far.
Theta is expected to remain over the eastern Atlantic for the next several days, according to the National Hurricane Center.
The system, which has maximum sustained winds of 85 kilometres per hour, was located 1,545 kilometres southwest of the Azores at 9:00AM GMT, the US-based agency stated in an advisory.
No coastal watches or warnings are in effect for the storm which is forecast to travel east into open waters before dissipating.
Another system, Tropical Storm Eta made landfall in Lower Matecumbe Key in late Sunday, bringing heavy rains and flooding to South Florida, and leaving thousands without electricity.
Eta was making landfall for the third time, having hit Central America as a Category 4 hurricane last week and impacting Cuba on Sunday.
The Atlantic season may yet be in for more storms, with the official end-date schedule for November 30.