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Climate scientists warn that New Zealand is on the brink of a marine heat wave after recording temperatures nearly two degrees above average in the North Island’s coastal waters.
Meteorologists from the National Institute for Water and Atmospheric Research (NIWA) said a marine heat wave is forming, with above-average temperatures reported throughout October, following a record warm winter.
A marine heat wave is defined as a prolonged period of extremely warm ocean temperatures, above the 90th percentile, that can extend up to thousands of kilometers.
The warmest seas are north of the North Island, where ocean temperatures are 1.6 degrees Celsius above the November monthly average. Sea temperatures off the coast of Northland range between 18 and 21 ° C.
NIWA meteorologist Ben Noll said temperatures in other parts of the country were 0.7 to 1.1 degrees above average.
“Nine times out of 10, Northland Sea temperatures are colder than they are now for the time of year. This makes what we are seeing now quite unusual, ”Noll said. “We are not even at the peak of sea surface temperatures, which usually occur during January and February.”
The news comes after New Zealand weather experts gave their predictions for next summer, which they said would be long, hot and dry, with an increased risk of wildfires and droughts.
“High pressure systems in October brought more sun, warmer temperatures and less wind than normal. This pattern caused the sea surface to heat up and prevented the cooler water below from mixing on the surface, ”Noll said.
New Zealand is in the middle of a La Niña year, which is often linked to warmer sea temperatures on both sides of the Tasman.
In 2018, New Zealand experienced the hottest summer on record, largely driven by a marine heat wave that caused sea temperatures to rise by as much as six degrees in some areas. The average ocean temperature during January of that year was 20.3 ° C, more than three degrees above normal.
The warm seas led to a significant influx of fish and marine life generally only found in tropical climates, including the Queensland groper, whose usual home is the Great Barrier Reef.
Other marine life that is rarely present in New Zealand waters and that marine observers have increasingly noticed include kingfish in Dunedin Harbor, garden eels in the Kermadec Islands (1,000 km north of New Zealand) , Sergeant Major Damsel, Striated Frogfish and Lord Howe Moray. in Northland and lion’s mane jellyfish in Wellington Harbor.
The 2018 marine heat wave also triggered a boom in land animals, including an explosion in the rodent population.
Warmer seas provide additional energy for passing storms, Niwa said, in addition to fueling warmer temperatures on land.
A marine heat wave this summer would mark the third in four years in New Zealand.
Warmer-than-average summer temperatures have been forecast for the next three months, following New Zealand’s hottest winter on record, which was 1.14 degrees above average.
Seven of the 10 warmest winters on record in New Zealand have occurred since 2000. “It just shows the trajectory we’re on,” Noll said.
