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A giant blob of warm ocean water is adding a decidedly different flavour to New Zealand’s El Niño summer – with plenty more extra heat and humidity likely to come over the first half of 2024.
The surprise wildcard comes as a climate scientist says marine heatwaves proved a major factor in what was our wider region’s hottest year in a century and a half of records.
Right now, moderate-to-strong ocean heatwave conditions were being observed over thousands of kilometres between eastern Australia, New Caledonia and eastward to the Chatham Islands.
“It’s a wide swathe, but the warmest blobs sit west, north and east of the New Zealand mainland,” Niwa meteorologist Ben Noll said.
“During an El Niño, you’d actually expect water lying between 20 and 35 degrees south [of the equator] to be cooler than average, but instead, it’s warm in that zone.”
Noll said the blob developed over December and likely contributed to the warm, wet weather that dampened New Zealand’s Christmas and New Year weekends.
This image shows current sea surface temperature anomalies in the region around New Zealand. Image / Niwa
“It also had an influence on temperatures over December, which was a month with relatively persistent northerly-quarter winds - that’s unusual for El Niño, but I guess not entirely unexpected given the odd form of El Niño that we have.”
Traditionally, El Niño spelled wetter summer conditions for New Zealand’s southwest, dryness in the north-east and persistent, widespread westerly flows.
This time, however, the system was unfolding against a backdrop of climate change and heat in both the west and east of the equatorial Pacific - raising the potential for sporadic visits from moisture-packed subtropical plumes like those that soaked the north last summer.
The recently formed blob added yet another dimension to the messy picture, he said.
“Given that [the blob] is expected to continue, air masses coming down to New Zealand are going to be moving across marine heatwave-affected waters, allowing them to retain that extra warmth and humidity,” he said.
This image shows marine heatwave conditions - colour-coded by strength - around New Zealand. Image / Niwa
“It’s something that we’re going to be watching pretty closely and I do think it’ll be a storyline as we go through the first half of the year.”
Niwa’s just-issued three-month outlook picked “very likely” above average temperatures for most of the country, along with near-normal rainfall in the North Island’s north and east of the North Island and west of the South Island and near or below normal levels elsewhere.
“Where we’ve seen dryness so far - which is across Manawatū, Whanganui, Wairarapa, Wellington and the top of the South Island down through Canterbury and Otago - these are areas where you wouldn’t necessarily expect it to be favoured during an El Niño summer,” Noll said.
“That’s especially the case in the western North Island, where typically those westerlies blow with enough vigour to routinely bring that moisture in.”
On the flipside, he said, northerly winds travelling over the warmed-up ocean water had ferried enough rain down to north-eastern areas to spare farmers El Niño drought conditions.
“The second half of January offers some additional rain for those areas.”
Meanwhile, climate scientist Professor Jim Salinger said the 4.2 million sq km area on and around New Zealand just experienced its warmest 12 months in records stretching back to 1871.
The year-end mean temperature for the whole region came in at 14.36C - which was only slightly above 14.35C in 2022, but still almost 1C above the 1951-1980 average.
“Seas around New Zealand were particularly warm, being 14.44C, or 0.96C above average,” Salinger said.
Further afield, local sea temperatures around Campbell Island and the Chatham Islands respectively measured 0.9C and 1.6C above normal, with the latter largely owing to intense marine heatwave conditions that persisted through to September.
Salinger cited the effects of La Nina, more anticyclones to the south and east of the country - and global climate change.
New Zealand has already warmed by about 1.1C in just over a century, while four of the country’s five biggest warm season heatwaves had occurred within the last six years.
With 2023′s warmth came plenty of wet, with insurers logging a record $3.6 billion worth of damage claims from massive weather events.
Niwa is this week due to release its official climate summary for 2023 which, as at last month, was tracking alongside 2022 and 2021 as one of New Zealand’s hottest years in history.
Jamie Morton is a specialist in science and environmental reporting. He joined the Herald in 2011 and writes about everything from conservation and climate change to natural hazards and new technology.
