In a tweet Tuesday night the National Meteorological Service said the system has the potential for development into a strong tropical wave or tropical storm passing south of Jamaica.
It said it is likely to become a threat and should be monitored closely.
The Miami-based US National Hurricane Center says the system, which is now a tropical wave, is producing shower and thunderstorm activity a few hundred miles east of the Windward Islands.
The system continues to show signs of organization and will likely become a tropical depression within the next two or three days.
The disturbance is forecast to move west-northwestward across the southern Windward Islands on Wednesday and then move toward the central Caribbean Sea late this week.
It put the formation chance over the next five days at 90 per cent.