Eight spots recorded mean summer maximum temperatures which were at least 3C warmer than average. Photo / Getty Images
Eight spots recorded mean summer maximum temperatures which were at least 3C warmer than average. Photo / Getty Images
Soaring temperatures in air and water over our hottest-ever summer has prompted climate agencies here and across the Tasman to jointly issue a historic statement.
The aim of this week's statement, issued by Niwa and Australia's Bureau of Meteorology, was to document the season's unusual weather patterns over the region as a historical record.
More than 50 places in New Zealand set new summer mean temperature records, and another 50 had their second or third-hottest summer on record.
The biggest change was in Masterton, where it was 3.2C above average this summer.
Meanwhile, Leigh, northeast of Auckland, had the highest mean temperature overall, hitting 21.8C.
Eight spots recorded mean summer maximum temperatures at least 3C warmer than average, and seven observed mean summer minimum temperatures at least 3C warmer than average.
Of these, the most extreme was Masterton, where mean night-time minimum temperatures were 3.6C warmer than average.
Th weather expert said sea-surface temperatures rose sharply in the southern Tasman Sea in November, reaching 2C or more above average over a wide area.
Niwa climate scientist Petra Pearce described the marine heatwave as "quite remarkable".
"It spread across the width of the Tasman and resulted in record heat in Tasmania and New Zealand," Pearce said.
"We would normally see something much more localised but this was very widespread.
"The 2017/18 summer is the only summer on record for New Zealand where the nationwide temperature was more than 2C above average."
Bureau of Meteorology senior climatologist Dr Blair Trewin said the conditions had a major influence on the summer in Tasmania, which had its hottest November-January on record.
The hottest summer on record also brought extreme rainfall events - including Cyclone Gita, which brought flooding to places like Riwaka, near Nelson. Photo / Tim Cuff
"We saw particularly warm temperatures in December, when the average sea-surface temperature in the southern Tasman Sea was more than 2C above the 1981–2010 average and 0.6C above the previous recorded high for any month."
The marine heatwave meant New Zealand's glaciers were stripped of last year's snow, but much of the country was hit by heavy rainfall events.
Subtropical and tropical storms that affected New Zealand during the summer kept characteristics usually present over warmer oceans, resulting in intense rain and large rainfall amounts not typically observed in New Zealand.
Victoria University climate scientist Professor James Renwick said the marine heatwave would be unusual even under climate change projections 50 years from now.
"But as time goes in, it's going to become easier for these types of events to happen," he said.
"And on the temperature side of things, as these extremes over summer become much more common, we're going to get higher temperatures all around the country, along with stronger rains, storms, winds and all of that."
