The agency also advised that gale-strength northwesterlies were possible in eastern areas of the South Island and the southern North Island.
Strong wind watches have been issued for the Canterbury high country, Fiordland, Queenstown and Southland west of Lumsden.
MetService meteorologist Alex Holden said a low pressure system was moving in off the Tasman Sea.
“It’s managed to grab a good stream of moist air from the subtropics and is just directing it straight onto the mountains and producing a lot of rainfall there.”
Holden recommended people keep a close eye on MetService’s forecasts for any upgrades to warnings, as well as the New Zealand Transport Agency’s website.
“We see that with heavy rainfall like this, driving conditions can be quite hazardous, and we’ve also seen infrastructure impaired by these sorts of events over the last few months.”
Warm sea surface temperatures in the West Pacific, currently tracking one to two degrees above normal, were a rainfall factor.
“That will definitely be energising [the system], making it moister and a better rain-producer.”
The front was forecast to weaken as it moved onto the North Island on Saturday.
Meanwhile, Holden said forecasters were watching another low pressure system building below New Zealand, and potentially arriving as a second moisture-charged system next week.
“From what I can comment on at the moment, it looks like a very similar scenario to what’s going to be happening over the end of this week.”
