Incoming wild weather could cause flooding and destruction like Cyclone Gita - forecaster

Whether Cyclone Oma hits New Zealand or not this weekend, Kiwis should brace themselves for a wild mix of heavy rain, wind, plummeting temperatures, and even snow.

Cyclone Oma is currently bearing down over the north of New Caledonia, where Niwa forecaster Ben Noll told Magic Talk's Peter Williams the storm was causing issues for meteorologists.

"It actually knocked out the radar system up there... that speaks to the strength of this system, and that is something we will be keeping a very close eye on," he said.

While it is still up in the air whether Oma will strike New Zealand, either way, Mr Noll said Aotearoa will still be battered from a wild mix of weather this weekend and into next week.

"It could still be a high impact... Oma or not, it does look like a high impact weather event occurs this weekend."

Mr Noll said an "impressive storm system" moving up New Zealand from the south could merge with moisture from Cyclone Oma dropping down from the Pacific and Australia.

"[It is] certainly not a time to let your guard down, there could be some heavy rain with that system, some high winds, maybe even high elevation snow in the South Island, and then temperatures that are more like a taste of late Autumn or early winter as we go into Sunday, Monday and Tuesday."

When asked by Williams if that system could bring flooding and destruction similar to that which Cyclone Gita set down on New Zealand last year, Mr Noll said that was very possible.

"The reason that could occur is because the soil right now is very dry, and that means it is kinda like concrete, so when the rain falls on that soil, that may just run off and not get absorbed by the ground," said Mr Noll.

Mr Noll said eastern parts of the South Island, such as Christchurch up to Blenheim, and Wellington likely to be hit hardest by the storm, with South Island towns forecast to get a lot cooler very quickly.

"They might struggle to get to 15degC as we go through Sunday into Monday and that is a massive change. Time to grab the jumpers."

But that doesn't mean people in other centres are off the hook.

"Everyone gets rain, everyone gets wind, everyone gets cooler," he said.

WeatherWatch on Tuesday said the cooler change will begin on Friday with temperatures dropping significantly over the weekend. Regions like Southland and Canterbury can expect highs to reach only 14degC.