“[It also means] the rain distribution differs slightly between the models, so there’s quite a bit of doubt at this stage as to where the heaviest [rain will hit],” Baillie said.
The lower half of the country is also tipped to see heavy rain as the front crosses the South Island on Thursday night.
Fiordland and the south of the Westland district are first in the firing line, followed by Dunedin and North Otago.
The National Institute of Water and Atmospheric Research (Niwa) said: “A vigorous sub-tropical jet stream will drive the development of a strong, slow-moving low later this week. This will coincide with an atmospheric ‘stop sign’ [blocking high pressure] east of New Zealand, likely leading to widespread rain, some heavy - and it may last a while.”
Baillie said the rain will continue into the weekend and possibly linger into Monday and Tuesday next week.
“There’s going to be periods of rain and showers after that main front goes through,” Baillie said.
The weather system will also push the unusually warm temperatures out to make space for chillier nights.
MetService meteorologist John Law said temperatures were “very warm for this time of year” over the last few days, but that will not last.
“We have been spoilt with some very unseasonable temperatures but it was a brief blip and we’ll be back to something much more familiar for this time of year.”
While New Zealand should expect heavy and widespread rain later in the week, Law said we are looking at a much better few days beforehand.
“[Today] and Wednesday look pretty good, with much more settled weather.
“It’s worth keeping an eye on the forecast because I think things will go downhill for the rest of the week.”
