The incoming storm and wild weather is "more than just a cold snap", according to MetService's John Law.
Speaking to Breakfast this morning, Law said the worst of the wild weather is expected to hit the country today and tomorrow.
"Today we're looking at those parts on the northern and western parts, New Zealand's seeing some of the heaviest rainfall and in the mix is some thunderstorms as well, especially for places like Northland, Auckland and the Coromandel.
"Some really intense bursts of rainfall, some heavy bursts of rain as it comes through, we are going to find more thunderstorms as it comes through this afternoon."
Law said floods and slips are also possible due to heavy rainfall in areas that are already very damp.
"We've got really wet ground, this has been a wet story so far in May and as the rain comes in its got nowhere to go so it may well cause things like some localised flooding and it may well cause some slips, particularly in those areas that are already very vulnerable.
"If you're out and about driving in these conditions as well, especially when heavy showers and thunderstorms come through, it will make things a little bit trickier so just take that extra bit of care when you're out in that rain this afternoon."
He said it's definitely worth keeping up to date with thunderstorm warnings and watches along with the rain radars.
Law warned temperatures are expected to plummet in some regions towards the end of the week and some may even see snow.
He said the daytime temperature will drop on Thursday, especially for places like Central Otago and the Central Plateau.
"It's going to be a real contrast to what we've been used to over the last week or so."
Law said while people should brace for wild weather, it should move through fairly quickly.
"I think because we've had so many warm temperatures over the last week or so things won't settle too long and too fast but if you're going to be crossing those high passes on the South Island, do keep that in mind."
He said drier weather and slightly warmer temperatures can be expected across the country as the weekend approaches.
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