Sea temperatures along the Otago and Canterbury coasts have risen “well above average,” prompting Niwa to declare a marine heat wave.
Meteorologist Ben Noll said water temperatures ranged from 1.1 ° C to 1.4 ° C above average in November, and daily sea surface temperatures were over 3 ° C above average around western and northern North Island and eastern South Island over the past week.
Sea heatwave conditions, classified when the sea temperature was above the 90th percentile for at least five days, had been observed in the waters off all parts of New Zealand.
He said this was on par with conditions seen in November 2017, which marked the start of an unprecedented sea heat wave in the country and in the Tasman Sea.
“Frequent patterns of high pressure near and south of New Zealand during November, due to La Nina, caused subtropical northeasterly winds to be more frequent than normal.
“The reduced wind speed during the month prevented the cooler groundwater ocean water from mixing with the surface.
“In addition, the amount of sunshine has generally been above normal, which has helped to warm the ocean surface. “
Mr Noll said marine heat waves were becoming more frequent in a warmer climate.
Between 2010 and 2019, 963 sea heatwave days were observed in the New Zealand region, compared to 366 between 2000 and 2009.
While milder seas might be good for beachgoers, marine heat waves have also been shown to have a severe effect on ocean ecosystems and the industries that depend on them.
During the 2017-18 event, glaciers melted as some pockets of ocean off the west coast of the South Island warmed to 6 degrees Celsius above average, while elsewhere , the mussel beds suffered cascading losses and the vineyards had early harvests.
Climatologist Professor Jim Salinger said La Nina means New Zealanders can count on widespread heat in the coming months.
Additionally, mild conditions could spell more bad news for New Zealand’s retreating glaciers.
“Although there has been heavy seasonal snow, especially around the southern lakes region, it will melt very quickly and then we will see the melt eat away at the permanent snow and ice later in the summer,” a- he declared.
Mr Noll said Niwa’s seasonal climate outlook for the summer will be released today.
– Additional reporting: The New Zealand Herald