Weather modelling predicts that the remnants of a downgraded Cyclone Gita will hit the upper South Island.
The cyclone - which caused damage to Tonga last week - remains a severe category 3 tropical storm as it moves into the northern Tasman Sea, although it is likely to drop to a category 2 cyclone Saturday afternoon or tonight, according to WeatherWatch.
"Gita remains an intense and serious storm with a huge amount of wind and rain around it," WeatherWatch's head forecaster Philip Duncan said on Saturday.
While American modelling had been picking a South Island landfall early next week, while European modelling was tipping Gita would hit the western side of the North Island.
On Saturday, both adjusted their predictions and are saying the upper northwest corner of the South Island will be struck.
"Of course this isn't yet locked in and with the storm still at least three days away, this could definitely still change," WeatherWatch said.
"However, it does highlight that both main islands of New Zealand are at risk from flooding and wind damage. In the coming days we expect this to still shift around a bit northwards and southwards."
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It is expected that Monday will be the day for certainty around where Gita will make landfall.
Gales and rain could extend from Dunedin to Waitomo, with travel delays expected for flights and any travel in the Cook Strait.
MetService, meanwhile, is urging people to be prepared for Gita.
Anyone with boats in lakes, rivers and coastal areas should check their moorings during the weekend, and drains and gutters should be cleared and trampolines tied down.