Heavy rain is expected to drench the South Island tomorrow and then make its way up the country - possibly hitting the already flood-stricken regions of Whanganui and Taranaki region hard on Friday.
MetService has issued a severe weather warning for Westland, Canterbury and Otago with heavy rain and gales expected to kick off about 2pm today.
Metservice meteorologist Emma Blades said a series of fronts would move east over the country from Thursday to Saturday.
The weather might become slow moving - meaning trouble for areas such as Taranaki and Whanganui, which are still cleaning up from severe flooding last month.
There was a low to moderate chance of heavy rain in Taranaki and the Bay of Plenty at this stage, she said.
"Whenever you get heavy rain, there's always that chance of flooding.
"It's going to gradually make its way up the country but the only areas [in the North Island] we're keeping an eye on really is around Taranaki and Waitomo possibly, and the Bay of Plenty.
"It's kind of a bit of a heads up, there might be something coming," she said.
Weather Watch head analyst Philip Duncan said it was "one to watch" for Hokitika and Whanganui.
The system definitely had the potential to bring flooding in some localised areas so people should keep up to date with weather watches, he said.
"It's very similar to that same front that came in two weeks ago that did bring flooding to Hokitika and Whanganui.
"The downpours are going to be heavy, the fronts going to be slow-moving, so it's one to watch but we're hoping it'll clear through a little bit faster and that will reduce the chances of any more problems in the North Island."
The downpour was also expected to hit Nelson, Buller and the Tararua Ranges on Friday with thunderstorms possible.
Severe gales could be seen in Marlborough, Wellington and south Wairarapa on Friday.