Tropical Storm Isaac was expected to continue strengthening, the National Hurricane Center said in its 11 p.m. advisory.
The storm was moving west at 8 mph in the eastern Atlantic, about 1,580 miles east of the Windward Islands. Isaac reached maximum sustained winds at 50 mph.
The system had been churning in the Atlantic as Tropical Depression 9 for most of Saturday at 35 mph, just under the 39 mph threshold.
It’s still too early to forecast whether Isaac could be a threat to South Florida, but it is expected to be a hurricane by early next week.