At 11 p.m. EDT, the storm's maximum sustained winds were about 75 mph, up from 40 mph at 11 a.m., the National Hurricane Center in Miami reported. Omar was expected to gain strength further Wednesday.
Forecasters warned Omar is likely to bring heavy rain in Puerto Rico and smaller islands in its path and to the northern coast of Venezuela. The rain could trigger flash floods.
The storm was also expected to bring heavy swells and battering surf.