This will bring rain or showers to most places, although it should clear from eastern areas north of Otago on Sunday.
"Although Christchurch is getting some drizzle and rain over the next few days, it should be gone in time for the Super Rugby Match between the Crusaders and the Chiefs on Sunday afternoon," MetService meteorologist Stephen Glassey said.
"Auckland is more likely to see showers for the game on Saturday night between the Blues and the Highlanders."
Niwa forecaster Ben Noll said the low forming up in the Tasman had been helped by a connection to subtropical moisture to the north of New Zealand.
"It's pulling moisture down from the likes of Fiji and Vanuatu – and even north-west of Vanuatu – so it's a nice little northerly connection," he said.
"We tend to see our best rainfall events, especially in northern New Zealand, when we have that tap of moisture from the tropics and subtropics turned on, and that's what's going on here. It also helps that we have this disturbance in the Tasman Sea."
WeatherWatch forecaster Philip Duncan expected the subtropical element making the rain heavier to linger in some regions for days, with more downpours coming to northern and eastern parts of New Zealand.
"By Monday a colder southerly change is arriving – but with a twist for northern New Zealand, as it may spark a small local area of low pressure which once again will drive in rain and showers," Duncan said.
"Across 2020 IBM data and even GFS data from the US Government has been fairly consistent at forecasting weak northern lows that have failed to truly bring rain.
"The difference with this set-up is that the 'blocking' high pressure system to the south has pushed further away from northern New Zealand than previous similar events – allowing the rain to sink south over land and not remain painfully close out at sea."
He added there was some resistance – the high pressure in the south was pushing back and that made for a very windy night in eastern Waikato with big gales over 100km/h roaring down the western side of Mt Te Aroha and into the Te Aroha township.
"A normal set-up with a windy easterly but this strong wind isn't caused by a storm – it's simply the squash zone of air pressure between a weak but large low in the Tasman and a strong high further south."
Noll said that, before this wet period, many northern spots had been on track to see their driest – or near-driest – June on the books.
Those places included Mangere and Western Springs (driest), North Shore (second driest), Cape Reinga, Dargaville, Whenuapai (third driest) and Whitianga (fourth driest).
"Some locations in North Island are likely to fall out of the running because of this rain – but it's still likely the January to June period will become the driest on record [for Auckland]," he said.
"So by all means, it is welcome that it's raining outside, but just because there are big puddles on the sidewalk, doesn't mean that the impact of what has been one of our worst droughts is over."
Auckland's current dam storage was currently sitting at 45 per cent, compared with an average 78.5 per cent for this time of year.
With a dry outlook for the rest of the year, Watercare this week described the situation as "critical".
