A tropical depression (TD05DF) to the west of Vanuatu is forecast to turn into a tropical cyclone sometime today.
The Fiji Meteorological Service says the cyclone might reach category 2 strength.
There is a tropical low advisory for Vanuatu with a yellow (moderate) alert for Shefa province.
New Zealand's National Institute of Water and Atmospheric Research principal scientist Chris Brandolino told RNZ Morning Report the system is forecast to move toward Vanuatu over the next couple of days.
"It is forecast to remain disorganised and overall weak for tropical cyclone standards," Brandolino said.
"But non the less, even weak tropical cyclones can produce very heavy rain and flooding so there can still be some impacts but at least it's not forecast to become anything overly significant, that is, category 3 or higher."
There have been seven tropical cyclones in the South Pacific so far this season.
There have been two cyclones over the this week and another one is brewing west of Vanuatu.
Ex-cyclone Nat by French Polynesia, and Osai south west of the Cook Islands, have been downgraded to tropical depressions.
Fiji's Metservice no longer has storm warnings listed for the Cook Islands, but there are two international marine warnings for tropical depressions.
Brandolino said more cyclones are forecast over the next 10 days in the South Pacific.
He said a packet of energy in the South Pacific is causing an uptake in tropical cyclone activity.
"Indications are that over the next week to 10 days we will probably see more.
"So I would not be surprised over the next week to 10 days if we see more activity over the south-west Pacific so there could be more to come."
Meanwhile, the Cook Islands emergency management office director John Strickland said tropical cyclone Osai did not cause any significant damage to Palmerston Island - the place that felt the strongest effects of the storm.
Strickland said the cyclone was downgraded to a tropical depression at about 7.30pm on Wednesday local time (Thursday, NZ time).
"Nothing significant to report apart from the normal rough seas but no inundation, winds have dropped and sunny now, the rain has dropped down in Palmerston Island and the people are safe, bottom line," he said.