January rainfall records have tumbled over what’s been an unusually soggy month for most of the North Island – and it’s not just La Niña’s warm and wet influence to blame.
MetService today reported a slew of new weather records, on the back of two storms that each brought to Auckland more than a month’s worth of rain within hours.
At Auckland Airport, Friday’s deluge made for that location’s wettest day (245mm) - and also brought half the total of what made for its wettest month (419.6mm) - in records stretching back more than 60 years.
It’s generally been the city’s wettest month ever, with rainfall levels sitting at a whopping 769 per cent of normal as at Monday – or nearly 40 per cent of its annual average – even before last night’s second rain-maker arrived.
Niwa reported this morning the latest system delivered 71mm to Western Springs in 24 hours – including more than 25mm within just 60 minutes – or the equivalent of a typical January’s rain.
Elsewhere in the North Island, it’s been a record-wet January at Hamilton Airport (234.8mm), Whitianga (522.6mm), Whangarei Airport (489.1mm), Tauranga Airport (385.3mm), Gisborne Airport (252.1mm) and Napier Airport (265.2mm), against rainfall data going back to 1935, 1987, 1943, 1910 and 1937 at those respective stations.
January was record breaking 🌧
— MetService (@MetService) January 31, 2023
Auckland Airport received around 6x their average January rainfall - a normal Jan-May amount 🤯
But it was very dry around southern parts of the South Island..
🥵Record breaking heat for Westport
These records are made more likely by La Niña 👀 pic.twitter.com/cOIhanzHLk
It’s also been the second wettest January on the books at Taupo Airport (187.8mm) and Kerikeri Airport (448.8mm), MetService revealed.
In another eye-opening figure, Niwa yesterday calculated Auckland (Mangere) had had a paltry 144 hours of bright sunshine over January – equivalent to 65 per cent of its January normal, and just five hours of sunshine each day.
By comparison, Wellington has received an average eight hours of sunshine each day over January.
Niwa Weather’s Ben Noll said the soggy statistics owed to a mix of climate variables that have spoiled summer for holidaymakers across the upper North Island.
An obvious one was a La Niña climate system that’s ripened the ocean-atmosphere state for humidity and rain in northeastern regions – and contributed to a record warm and wet 2022 for New Zealand as a whole.
Over the past 24 hours, 71 mm of rain has fallen at our Western Springs climate station in Auckland.
— NIWA Weather (@NiwaWeather) January 31, 2023
This is a month's worth of rain... again.
Much of this fell in only a few hours.
Including:
🌧️ 25.2 mm in 1 hour
🌧️ 44.2 mm in 2 hours
🌧️ 58.6 mm in 3 hours pic.twitter.com/lZqhfjM8gc
It’s also helped set up a dramatic contrast in regional weather patterns across the country.
While a slew of rain-makers have saturated North Island soils with excess moisture, swathes of the South Island are running noticeably drier than normal – and pockets of Southland and Otago stand on the verge of meteorological drought.
It happens to have been Invercargill Airport’s and Wanaka Airport’s driest January in more than 30 years of records – just 23.6mm and 4mm fell at those locations respectively last month.
January also brought Westport Airport’s hottest day (29.1C) in records than began in 1965.
On Sunday, as Aucklanders were cleaning up after Friday’s floods, the mercury hit 34.2C in Alexandra – equaling the hottest temperature observed in New Zealand so far this summer.
Noll cited some other big-picture drivers behind the upper North Island’s miserable month.
Northern regions had also felt the reaching influence of a persistent band of cloudiness and storms called the South Pacific Convergence Zone.
Friday’s floods happened also to coincide with the Madden Julian Oscillation – a pulse of rain and thunderstorms that circles the globe every 30 to 60 days – enhancing rainfall in our part of the planet.
This has all played out against the backdrop of a warming climate, which studies show have been contributing to extreme rainfall events here and elsewhere.
“All of these things wouldn’t have given us this outcome by themselves – but when you put all these puzzle pieces together, you can see why we have this picture of flooded landscapes.”
Niwa is expected to release its summary for the month in the next few days.