'A year of two halves': 2017 weather breaks records

Monday, 8 January 2018

2017 was NZ's fifth-warmest year since records began.

Last year was the fifth warmest year on record in New Zealand and one in which swings between extremes toppled longstanding records nationwide.

Niwa's annual climate summary for 2017, released on Monday, shows the year's weather was hard to pin down: it was largely defined by warm temperatures and high rainfall, but ended with record-breaking dry-spells and meteorological drought.

For most of the country, 2017 was warmer and wetter than usual, the report says. All six major cities had clocked up their usual annual rainfall before the end of September and had been on track for record wet years.

2017 was a wet year for much of the country.

Many areas broke or nearly broke various high temperature records. No locations broke low annual temperature records.

The year's weather was caused in large part by prevailing high pressure patterns in the east, with northerly winds. The year ended with a marine heatwave and a high pressure system, leading to warm, settled conditions.

Of the major cities, Auckland was the warmest, Dunedin the coldest and driest, Tauranga the wettest and sunniest, and Wellington the most dim.

The average air temperature nationwide was 13.15C, about 0.5C above the long term average. That made it the fifth warmest year since 1909, beaten by 2016, 2013, 1999 and 1998.

While much of the South Island and lower North Island had near normal temperatures, temperatures were above average further north.

Heavy rain causing flooding in parts of New Plymouth. Many communities experienced floods in 2017.

The exceptions to the overall trend were in the deep south - Southland and Central Otago were notably drier than usual.

A HOT STREAK

As the year came to an end, the country was in the midst of a record warm streak.

August, September and October was the equal warmest three month period in New Zealand since 1909, Niwa principal forecaster Chris Brandolino says.

'We had exceptional warmth in each of those months, in particular August, where the temperature was 1.3C above average,' he says.

That streak continued. December was 2.4C warmer than usual, ony the third time average temperatures had been above 2C in a given month.

'This was an incredible month,' Brandolino says.

'The month of December was exceptional, temperature wise - The nationwide average temperature was 18.1C, that's 2.4C above the long term average.

'There were 90 locations where the mean temperature were a record or near record value - a top four finish.'

Cromwell had 23 consecutive days above 25C, ending the month more than 3C warmer than usual.

IT RAINED UNTIL IT DIDN'T

The defining weather events for the year were a series of storms, which were major contributors to high rainfall totals.

In particular, the 'Tasman Tempest', Ex-Tropical Cyclone Debbie, and Ex-Tropical Cyclone Cook earlier in the year had major impacts and contributed to record or near-record rainfall.

'New Zealand's climate during 2017 will be remembered chiefly for a string of high impact and record-setting rainfall events, mainly during the autumn season,' the report says.

The wettest places compared to usual were on the east coast, particularly around the Coromandel and Tauranga, where rainfall was about 40 per cent above long term-averages.

Some areas hit by storms ended the year with near record rainfall totals. Oamaru was hit by a storm in July, which dropped four months of rain in one day. It had its second wettest year ever despite ending 2017 with a dry spell.

While the year was defined by rain, the dry spells near the end broke records in themselves. The report says in terms of rainfall, it was a 'year of two halves'.

Christchurch had a 47-day dry spell, the longest in many decades, whilst in the midst of one of its wettest years on record.

While some low temperature records were broken, they were far exceeded by high temperature records.

Three places had their warmest years on record - Te Puke, Wairoa, and Lauder (near Clyde in Otago).

Auckland at Whenuapai had its second warmest year on record, as did Hastings. Dozens of other areas had near-record warm years.

WARMTH AND SUNSHINE

In terms of sunshine, the top of the South Island was once again the place to be.

The wider Nelson area ended the year with 2633 hours of sun, followed by Marlborough with 2605 hours.

Several other places were sunnier than usual. The South Island's West Coast, for example, had a particularly sunny year: Westport, Hokitika and Greymouth all surpassed 2000 sunshine hours, which made them sunnier than most major cities.

The warmest places were in the far north. Leigh, north of Auckland, had the warmest average temperature of 17C, followed by Whangarei and Kaitaia.

The driest towns were all in Central Otago. Clyde, Cromwell and Alexandra all had less than 300mm rainfall for the year.

Two places recorded that much rain in a single day: Castle Mount and Milford Sound.

Every month was warmer than average except for January, which was 0.7C below average.