Editorial: 2023 is shaping as the Year of the Big Wet

EDITORIAL

The MetService graph comparing this year’s daily rainfall with previous years fittingly looks like a worm struggling to get a breath above rising floodwaters.

It’s a sensation many are familiar with as a record
amount of precipitation has inundated the motu.

This week, MetService reported Auckland has been drenched with nearly an entire year’s rainfall in fewer than five months, with totals running almost three times above average.

Weather station data from Auckland Airport showed a whopping 1018.6mm of rain has fallen there since January 1, just over 90 per cent of the annual average.

Lift-off occurred at the end of January with the first of the extreme events, notably the one-in-200-year Auckland Anniversary Weekend deluge that contributed to the city’s wettest month in at least 170 years.

“Certainly, 2023 is the wettest start to a year [in Auckland] by a considerable margin,” MetService meteorologist Andrew James told the Herald.

The situation is wearying, with the start of the year especially overcast for Aucklanders, who received a paltry five hours of daily sunshine over January,

Why has this happened? We can thank Jamie Morton of the Herald, who elicited an explanation from MetService meteorologist Andrew James.

James singled out La Nina as the culprit. The ocean-driven climate pattern – known for causing muggy, wet conditions in the northeast but a drier flavour to the south – has played with our weather since the start of the decade.

“[The rain has] been mostly driven off the back of La Nina, which has made it easier for these systems to come out of the north toward us,” James said.

“We’ve had lots of very warm air coming over New Zealand as a result of La Nina, and warmer air can hold more moisture than cooler air, so we’ve seen significant rainfall right across the north, from Taranaki upward.”

The stage had already been set by the negative phase of another climate phenomenon called the Indian Ocean Dipole – a big cause of 2022′s record-wet and warm winter – and local pressure systems unfortunately positioned by a positive Southern Annular Mode.

Rain-makers had also been intensified by regional marine heatwaves, the damp influence of the equator-circling Madden Julian Oscillation and ongoing climate heating that’s loading more moisture into the atmosphere.

While the La Nina system itself dissipated earlier in autumn, its effects were still lingering in an ocean-atmosphere lag that meteorologists have partly attributed to this month’s soaking.

So will this dousing continue? How high will the worm on the MetService graphic climb by the end of the year? Well, not so much, apparently, as we are heading into a drier winter.

Coming in La Nina’s place is its counterpart climate pattern, El Nino. This spells a potentially record-hot year for the planet, but a shift to cooler, drier conditions across much of New Zealand. Read that again, cooler and drier.

The next event to watch for is a low moving towards the North Island on Thursday next week, with Weatherwatch saying it looks like it will just miss Aotearoa, moving down and away to the southeast. “Perhaps East Cape may catch some rain as this low moves through.”

The current conditions affecting New Zealand are coming from Typhoon Mawar, currently in the northern Pacific. Niwa reports the pulse of energy that caused the typhoon is moving east and reducing equatorial trade winds. Because of this, our early June pattern may have more high pressure.

In the short term, there’s good news that temperatures this weekend are expected to be warmer than the past couple of days.

Tomorrow’s forecast is mainly fine south of Taihape, but scattered showers elsewhere, turning to rain about and north of Auckland in the afternoon, some possibly heavy and thundery in Northland. In the South Island, there’s predicted to be periods of rain in the west and isolated showers for Buller. Showers increasing in Nelson and fine in the east with high cloud.

On Monday, rain is expected to spread to the southeast of the North Island, possibly remaining heavy in the north, easing to showers in the evening. Rain is predicted to be widespread in the north and west of the South Island too, some possibly heavy.

Cloudy elsewhere – with, naturally, a few spots of rain.

Heads up, worms.