It's been an unusually wet and cloudy summer for Auckland - with a dominant La Nina pattern and a slew of subtropical storms much to blame for the record rainfall. Photo / Michael Craig
It's been an unusually wet and cloudy summer for Auckland - with a dominant La Nina pattern and a slew of subtropical storms much to blame for the record rainfall. Photo / Michael Craig
How do we measure just how miserable this summer’s been for Aucklanders?
We can use a rain gauge: Nearly 600mm has fallen over our largest city already this season, with plenty of the wet stuff yet to come.
We can turn to sunshine hours - something even the notoriously gloomycapital scored better on than Auckland last month - or humidity percentage values that have often hovered hellishly in the 80s and 90s.
Or we can simply boil it down to two words: “Bummer summer”, as Ben Noll put it, borrowing a title the Niwa meteorologist earlier gave to Wellington’s dismal 2016-2017 run.
The season’s running rainfall total now stands at 598mm in Auckland – or 326 per cent of normal – easily locking in a record-wet summer with weeks to go.
The bulk of that, of course, came with the city’s wettest month – 539mm dropped on Albert Park in January – and its wettest day, the one-in-200-year event that was January 27′s freak deluge.
Within the space of only a month, beleaguered central city residents were doused with nearly half the rainfall they usually get in a year, or eight-and-a-half times what a typical January would bring.
It’s hardly been beach weather in Tauranga, either, where it’s been the wettest summer since 1962-63, when Keith Holyoake was Prime Minister and just a few hundred thousand people had access to televisions.
It hasn’t been quite as dreary in Wellington, but not sparkling, either: The capital’s so far had its seventh-wettest summer since 1972.
Look further south, however, and we see a glaring contrast: Large swathes of Otago and Southland are running “very” to “extremely” dry, just one step from full-blown drought.
Colour-coded Niwa maps measuring current soil moisture anomalies show areas like Buller, Southland, Otago and coastal Canterbury painted in yellows, ambers and browns – a dramatic difference from the dark blue covering most of a deeply-saturated North Island.
Source / Niwa
As Aucklanders received a paltry five hours of daily sunshine last month, spots like Wanaka and Invercargill chalked up their driest Januarys in decades of observations.
Noll has described this oddly split picture as a “tale of two islands”, with one obvious culprit to blame: La Nina.
The ocean-driven climate pattern, which has been meddling with our weather since the start of the decade, was notorious for bringing muggy, wet conditions to the northeast but a drier flavour to the south.
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.
Then, in January, we saw rain-makers 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.
The good news for the sodden north was La Nina was finally shuffling off, likely to be replaced by its opposite, El Nino, later in 2023.
But it would likely take months for La Nina to fade out entirely into the “Enso-neutral” state that sits between the two influential systems.
Niwa’s February-to-April outlook picked the potential for more subtropical lows and flood-making “atmospheric rivers” around the upper North Island, with rainfall totals likely to stay above normal.
“So, La Nina won’t be bringing its car to a stop suddenly – more just gradually easing pressure on the accelerator.”
