As New Zealand begins mopping up after the first big storm of 2018, scientists have made a big prediction.

Last year was one of New Zealand's hottest on record - and our most extreme when it came to costly weather-related disasters.

So what will 2018 hold?

Climate scientists have predicted the year will again be among the warmest ever - and, for the next few months at least, hotter than normal in our corner of the planet.

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Niwa has predicted temperatures between now and the end of February will be above average in all regions, while rainfall totals will be above normal in the north of North Island, and near or above normal in the east of the island.

While rainfall would be near normal elsewhere in the North Island and in the north of the South Island, the rest of the south could see less rain than usual.

It's already been an abnormally hot summer for many parts of the country.

Niwa climate data showed much of northern New Zealand, including Auckland, along with the lower and eastern North Island had been tracking at 2C above the mean average over the past month.

While the large majority of the North Island typically experienced mean temperatures of 16C and 20C over that period, the observed mean had been at least 20C in many northern spots, including Auckland.

With the exception of eastern and southern areas, the month-long temperature anomaly had also been experienced in nearly all of the South Island.

Climate scientist Dr Jim Salinger said the UK Met Office's global temperature forecast had indicated 2018 would be another warm year - but still not a record-breaker, thanks to a moderate La Nina system over the Pacific.

The Met Office forecasted the 2018 would bring a global average temperature of between 0.88C and 1.12C above that recorded between 1850 and 1900.

That was in line with an increase of between 0.28C and 0.52C above the 1981-2010 long-term average of 14.3C.

The current La Nina event meant global average temperatures would be around 0.1C lower than would be otherwise expected for 2018.

But for New Zealand, the La Nina - which has already given sun-seekers an especially balmy early slide into summer, and fuelled a marine heatwave engulfing the Tasman Sea - would bring above-average temperatures.

The Met Office and other agencies had forecast the event to last throughout Autumn, Salinger said.

Last year was New Zealand's costliest ever for weather-related insurance claims. Photo / File
Last year was New Zealand's costliest ever for weather-related insurance claims. Photo / File

Lows in the Tasman Sea, and highs to the south and southeast of the South Island, further suggested there would be more northeasterlies over the country.

"The upshot of all this is weaker westerlies over southern New Zealand."

Models also suggested New Zealand's marine heatwave, which has pushed coastal water temperatures to more than 2C above average, wouldn't fade out until next season.
It was therefore likely temperatures - potentially reaching up to 1.5C above average at times - would remain warm until May, he said.

But the climate over the second half of 2018 was much harder to predict, and would depend on what played out with an El Nino/Southern Oscillation event in the Pacific, and whether the westerly winds grew stronger or weaker than normal across the country.

"Summing it up, with the warm start to the year, and a warmer globe, then New Zealand temperatures are estimated to be between 0.5C to 1.5C above the 1980-2010 normal."

It follows a year that, as at last month, was tracking at somewhere between the fourth and seventh warmest in New Zealand's history.

Niwa scientists are due to release their annual climate summary next week.

Globally, it was the hottest year where temperatures hadn't been influenced by an El Nino event.

Civil Defence officials also declared a record number of weather-related state of emergencies - eight compared to one last year and four in 2015.

It proved our most expensive weather year for insurers, who paid out $242m for extreme events that hit the country in the first seven months of 2017 - a figure five times that of 2016's bill for extreme weather.

NZbrokers, one of the country's largest insurance brokerage groups, reported the number of storm and flood insurance claims in New Zealand has increased by 56 per cent over the last three years and this was accompanied by a significant spike in the cost of claims.

The Global Facility for Disaster Reduction and Recovery, which was partly funded by the World Bank and used to evaluate the threat of natural disasters in countries around the world, had now ranked New Zealand at a "high hazard" level for most flooding and cyclone events.

"While we were already rated as a high risk for seismic activity, now storm and flood losses in our market are on their radar as well," NZbrokers chief executive Jo Baker said.

"Weather events may cost less than a serious seismic event but the increasing frequency and geographic spread of events show every business in New Zealand should be prepared."