Dominica closed its international airport for a second day on Friday, while St. Lucia ordered businesses to close for half the day. A ferry that travels to Guadeloupe, Dominica, Martinique and St. Lucia also has temporarily suspended service.
No damage or flooding has been reported on islands affected by the storm. Gusts of up to 63 mph (101 kph) were reported in some areas.
The National Hurricane Center said Ernesto is located about 90 miles (140 kilometers) west of St. Lucia near midday with top sustained winds of 50 mph (85 kph).
It is moving at 21 mph (33 kph) and is expected to strengthen into a hurricane by Monday.