As of Wednesday afternoon, the disturbance was about 700km west of Rotuma and moving east.
Fiji Meteorological Service director Misa Funaki said people, especially in the maritime islands, were being warned to expect rough seas, heavy rain and strengthening winds.
"As [of Wednesday afternoon], it is still located about 1000km northwest of Nadi, it is slowly moving eastwards. Its current projections are projecting for it to head towards Vanua Levu, and we are looking at around Friday for this to occur.
"Some projections they are keeping it at a category one, while some are also projecting for it to become a category two system, but we are keeping a lookout on this."
The projected cyclone, on its current path, also poses a threat to Tonga's main island, Nuku'alofa.