7 Nov 2023

October unusually wet and windy - NIWA

4:20 pm on 7 November 2023
A truck that blew over, blocking SH1 just south of Waipara, Canterbury on the morning of 26 October, 2023.

High winds saw a truck overturn in North Canterbury on 26 October. Photo: Supplied / Waka Kotahi

For anyone feeling particularly wind-blown recently, NIWA agrees with you.

The National Institute of Water and Atmospheric Research has released its Octoberclimate summary.

It reported large temperature swings and high winds across the motu.

Kaikohe in the Far North had its wettest October ever, with 321 percent of its normal monthly rainfall.

The highest gust was on the West Coast - 232kmh on 26 October.

NIWA's Chris Brandolino told Morning Report's Susie Ferguson that former Tropical Cyclone Lola had "grazed" the upper part of the North Island, particularly Northland, Coromandel and the Bay of Plenty with "a good drop" of rain towards the very end of the month, which lifted the total monthly rainfall.

But temperatures were normal - which NIWA defined as plus or minus 0.5C of the average.

"When you look at the big picture it was pedestrian. [Nationally], the average temp was near average and we were at... plus 0.4C.

Beyond the average, there were wild variations across the country, he said.

"When you dive into the detail there were a lot of swings in terms of temperatures, and that was expected.

"Part of that is because it is spring, and spring is inherently a very changeable time of year. But it is also because of El Niño helping to drive those temperature swings and changes, and with that you often get the winds."

He said New Zealand - particularly the South Island and lower North - was likely to experience more of these intense and potentially damaging wind gusts over the next two months.

"With El Niño we tend to have higher-than-normal air pressure near and just northwest of the country and lower pressure in the south.

"Low pressure is a hole in the atmosphere and Mother Nature wants to fill that hole with air. If the 'hole' and 'mountain' are close together, that air is going to flow pretty darn quickly.

"With El Niño we have that mountain, or high pressure, near the upper North Island and the hole in the south, and often times they can be quite polar in terms of height and depth, and that enhances the wind."

Brandolino said "really hot temperatures" were on the way when the winds "swing around" from Australia.

"That will be a theme (in the) second half of November - some pretty warm, if not hot, days are coming up. Wind will become more west, norwest in time and that, combined with high wind, (means) there's a fire risk so these are things to be mindful of in the coming weeks and months."

Temperature

October brought large swings in temperature, a NIWA climate summary shows.

Temperatures for the month were above average in the North Island from Northland through to Gisborne - as well as for parts of Canterbury and Otago in the south, the National Institute of Water and Atmospheric Research (NIWA) said.

While below average temperatures were seen in the central and lower West Coast.

The highest October temperature was 29°C, at Kaikōura on 26 October.

While the lowest October temperature was -5.3°C, at Mount Cook Airport on 28 October.

But although there were several extreme temperatures throughout the month, NIWA said the westerly winds that had delivered above average temperatures at times through the month were offset by periods of sharply cooler southerlies, leading to a nation-wide average temperature just 0.4°C above the October average, ending up at 12.5°C.

NIWA meteorologist Seth Carrier said the two extremes averaged themselves out in most places, meaning temperatures generally ended up near average for most locations.

Wind

Wind was a defining feature of the month, NIWA said.

"There were multiple damaging wind events that especially affected the east of the South Island, but also affected the lower portions of the North Island," Carrier said.

The report highlighted multiple occasions across the month where high winds stopped flights and caused damage and power cuts, particularly in the South Island.

The highest wind gust was 232kmh, at Cape Foulwind on the West Coast of the South Island, on 26 October.

Rainfall

For much of the country rainfall was below normal during October, but Northlanders experienced a wet end to the month.

"That was really mostly driven by the remnants of ex tropical Cyclone Lola, which came through in the last few days of October and the heaviest rain from that ex tropical cyclone really hit really hit Northland hard," Carrier said.

The highest rainfall recorded in a day during October was 150mm in 24 hours at Kaikohe on 29 October.

Kaikohe also had its wettest October on record, with 321 percent of its normal monthly rainfall.

Meanwhile, of the six main centres, Auckland was the warmest and least sunny, Christchurch was the coolest and sunniest, Tauranga was the wettest, and Dunedin was the driest.

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