Why record sea surface temperatures are going 'off the chart'

Monday, 4 December 2017

Thanks to La Nina, the whole country is facing warmer than usual temperatures for the whole summer.

Near-record sea surface temperatures are being described as 'off the charts' - and New Zealand could be on track for another record year, Niwa says.

A La Nina pattern and higher than normal atmospheric pressure are warming sea surface temperatures by more than 6 degrees Celsius in some areas, compared to the average for this time of year, bringing warm weather to New Zealand.

People enjoy the fine weather on the beach at Maraetai, Auckland.

La Nina, a major systematic global climate fluctuation, influences sea temperatures in our part of the world, but Niwa forecaster Ben Noll said there are other factors driving the temperature higher.

'La Nina sits in the background as big driver of the change, but it's at the top of a pyramid of other factors,' Noll said.

Kahurangi Marine Reserve covers approximately 84 square kilometres and is one of New Zealand's largest marine reserves.

* Warm seas around New Zealand could take edge off cold snap**

A very impressive marine heatwave is unfolding near the east coast of #Australia, across the Tasman Sea, and in New Zealand coastal waters … average anomaly is +1.98°C and max anomaly is a gaudy +6.16°C off NZ's West Coast. pic.twitter.com/shDPuEcnn1

— Ben Noll (@BenNollWeather) December 1, 2017

WHY IS THE SEA SURFACE WARMER?

'One of those is we have much higher atmospheric pressure than normal which has a large effect on conditions,' Noll said.

When higher pressure is in the atmosphere it creates tranquil weather which calms conditions over land and sea, and leads to less wind.

'Winds are what churn up the sea and bring colder seas to the top, and with high pressure you don't get that mixing so the sea at the top is stagnant and is heated more effectively by the sun with no storms mixing it up.'

During La Nina events, the trade winds strengthen, and the pattern is a more intense version of the normal conditions.

'But this year the intensity has turned up several notches to what we have previously seen,' Noll said. 'This year is off the charts, truly exceptional.'

Noll believes we could be on track for a record year as sea surface temperatures are rivalling previous boom years in 2007 and 2010.

'The difference in the average is higher, and in some places much higher this time around,' said Noll. 'The difference above average is 2C, but in some isolated areas located west of New Zealand have 6.5 degrees higher than the average.'

It's an impressive and extreme difference when only a year ago the temperatures for this time of year were between 12C and 14C, he said.

'At between 18C and 20C, the East Coast of Australia and the West Coast of New Zealand have the warmest anomaly on the globe right now.'

It could also mean fish that enjoy warmer water – such as snapper, albacore tuna and kingfish – stay in New Zealand waters longer.

DOES THAT HELP THE FISHERIES?

Niwa fisheries scientist Malcolm Francis said fish such as snapper spawn in the warmer water, 'so that could start earlier if the temperatures continue to rise, and ultimately improve our snapper fish stocks'.

However, it would take about four years for the snapper to mature before the effect can be measured, he said.

The Ministry for Primary Industries is set to review snapper numbers over the next three years by electronically tagging 100,000 of the fish - a decision welcomed by experts from various fishing sectors.

Albacore tuna is a common fish trawled for by vessels off the West Coast, as they move from Auckland down to Westport.

'It means they could hang around our waters for longer which could be could for the fishing industry,' Francis said.

Kingfish and kahawai also enjoy the warmer waters, he said. 'We usually seem the in the South Island in autumn but that may happen earlier this year.'

But it could negatively impact some species that prefer cooler water, he said.

DROUGHT-LIKE CONDITIONS

Nationally, the first weekend of summer was marked by scorching temperatures, and Monday is expected to be even hotter.

While the warmer weather might be good news for fisherman and beach goers, the warmer conditions are expected to plague farmers.

Southland has had its driest start to summer since 1990, and environment Southland director of science and information Graham Sevicke-Jones said the region had only received only 81 per cent of its annual rainfall to date.

'It was unlikely the shortfall would be met with less than a month to go in the year,' Sevicke-Jones said.

River levels will continue to drop and the aquifers were not recharging, he said.

Southland District Council has now put in place hosing restrictions for all water supply schemes throughout the Southland district until further notice.

The council said reserves were being lowered by heavy water usage due to the warm weather.

Following a seven days of no rain, Wellington authorities have also issued a sprinkler-use ban to save water - a move unusual this early in summer and the call has gone out to save water where possible.

According to Niwa, Wellington is coming off its third driest November on record, but coming after the wettest November on record in 2016.

MetService is not forecasting any rain in the capital until Monday next week but even that, the national weather forecaster is first to admit, is far from certain.

Wellington Water spokesman Alex van Paassen said Wellingtonians had responded well and water use in the the capital had dropped from about 180 million cubic metres per day to 160 million.

'This is really good because we don't have to use water from the [Kaitoke reservoirs] lakes.'