Forecasters in Fiji say a tropical depression, with the potential to form into a cyclone, will bring damaging gale force winds to northern parts of Vanuatu tonight.
The Fiji Meteorological service says heavy rain, including squally thunderstorms are expected to hit the north of the Vanuatu island of Espiritu Santo overnight.
It expects flooding including sea flooding of low-lying areas and damaging, heavy swells.
Forecasters say the potential for the system to develop into a tropical cyclone within the next 24 to 36 hours is moderate to high.
The joint typhoon warning centre in Hawaii says there is a "good" chance of the formation of a tropical cyclone in the area about 880 kilometres north west of Fiji in the next 24 hours.