“What we had during March was the MJO being more active over in the eastern Pacific, which helped give us those very different weather patterns as compared to previous months, when we had La Niña and more northerly winds .
“But what we have coming up in the second week of April and mid-April is a brief return to the La Niña-like flavour of weather that we had over the summer season.”
“That perhaps won’t be the most welcome news for folks, namely in northern and eastern North Island, who’ve been enjoying the dryness that March largely brought.”
That change would start to be felt from Thursday to Saturday, as a subtropical low moved down toward the north and east of the North Island.
“This system looks to bring some rain, but it might stay just far enough offshore that we don’t receive copious amounts,” he said.
“Then, as we go from Sunday night and into Monday – and possibly continuing into next week – we’re going to have more low pressure moving in from the Tasman Sea.”
While the long weekend would start off with widespread fine conditions in the South Island, this second low would bring a marked shift across the south – and then to the rest of New Zealand.
“This could come with a fair bit of instability, and maybe enough energy for widespread thunderstorm activity, given it could be charged up with some warm, humid air from northern Australia.”
It wasn’t the only system forecasters were expecting over the first week of the school holidays.
“It looks to be a pretty busy week, with the potential for frequent rain, strong gusty winds and thunderstorms.”
With our climate state now in an “ENSO-neutral” holding pattern – meaning neither La Niña or El Niño was shaping conditions – Noll said we were more exposed to more variable weather, such as stormy pulses from the MJO.
As an El Niño continued to build, however, winter conditions may follow a tidier path – and also prove cooler and drier than the record-warm – and in last year’s case record-wet – seasons New Zealand has experienced so far this decade.
“That certainly will also contrast with what we’re expecting out to mid-April.”
Earlier this week, Niwa forecaster Chris Brandolino told the Herald that Kiwis might well notice cooler temperatures over what will be our first El Niño winter since 2015.
“Because we’re entering El Niño in the tropical Pacific, our airflows are going to be changing,” he said.
“What that means for New Zealand is that we tend to get more southwest winds during the autumn, and more southerly winds during the winter.
“So, it’s very likely that as we progress through autumn, especially May, and as we enter the winter season, we’ll see a propensity for more southwest and southerly winds.”
While the winters of 2020, 2021 and 2022 had come in at 0.97C, 1.16C and 1.2C above average respectively – each coming in at the warmest on the books – this season’s temperatures are likely to hover closer to average.
“We’ve had record-warm winters, so people have developed a recency bias [regarding] what winter is like.”
