There is increasing confidence a tropical cyclone brewing between Vanuatu and Fiji could strike New Zealand in the lead-up to Christmas, forecasters say.
Modelling shows the weather system will build near the Pacific Islands mid-next week before pivoting into the Tasman Sea and towards Aotearoa around the summer solstice - about December 21.
NIWA says for now, there's just a cluster of rain and thunderstorms north of Fiji, but predicts it will develop into a tropical cyclone early next week. If it does, Fiji, Vanuatu and New Caledonia could be in the firing line.
Weather Watch head forecaster Philip Duncan says he expects the Fiji Meteorological Service will declare the storm a tropical cyclone on Sunday.
He says data shows the cyclone could be a category 3 - indicating sustained winds of up to 157km/h and gusts of as high as 225km/h - and warns that Kiwis should be wary.
"New Zealand is in the risk zone for it," he says.
"It's not guaranteed to hit us - not at all - but this far out, to be seeing a storm like that in this area, it means it's one for us to keep a close eye on."
One of the reasons there is so much uncertainty about whether it'll impact New Zealand is because high pressure is forecast over the country at the same time, which may keep it at bay.
Duncan says the high will act like 'traffic lights' for the cyclone.
"This high will decide if this tropical low moves into the Tasman Sea, northern New Zealand, or pushes it out to our east with little impact on us," he explains.
"This high will also decide how soon the storm can track down here, perhaps giving it a red light for a week to remain up over New Caledonia waters."
The South Pacific Ocean recently moved into tropical cyclone season. The season lasts from November 1 to April 30, and comprises about 10 tropical cyclones in that period - only one of which will affect New Zealand on average, MetService says.
Last week, NIWA revealed in its seasonal climate outlook that New Zealand would be at "elevated" risk of significant rainfall, damaging winds and coastal inundation during the tropical cyclone season.
The forecaster said Kiwis would be in store for a dry start to summer, but that "moist, subtropical disturbances" could bring heavy downpours and flooding to New Zealand as it goes on.
It also said air temperatures would be above normal throughout the country, alongside a marine heatwave and elevated humidity levels in the North Island.
