It's become a hot topic over farm fences across the country, but Bruce Wills has been preparing for this El Nino since 2007.
That was the year that Trelinnoe, the northern Hawkes Bay sheep and beef farm he runs with brother Scott, went six months without rain in what was one of the worst droughts in recent history.
"Our entire property turned to dust - it was a real disaster and it knocked us for six, so afterward we sat down and said, what have we learned?"
Eight years on, the farm at Te Pohue, just off the Napier-Taupo Road, is vastly different.
"It tipped our farming operation upside down to become more resilient, and I think our farm now is reasonably robust and drought-tolerant."
Ahead of what's forecast to be the most severe El Nino summer since the disastrous El Nino of 1997/98, stock are being sold six weeks earlier than usual and hard work is going into maintaining good pasture cover now before the big dry hits.
Like most other farmers, the brothers are also applying fertiliser earlier than normal.
"We know what our demand profile for grass is like over the season, and we're also being vigilant with our lambs and anything else that we've planned to sell over the next few months.
"We are getting stock up to heavy weights as quickly as we can, because we know that once the moisture drops, we may have to dump them sooner rather than later."
Elsewhere, farmers had prepared extra hay and silage for summer and autumn, and in some cases, were putting summer crops in.
Dairy farmers, already hit by a low payout, faced a particularly tough time, and in areas like Northland and north Canterbury, stock rates still hadn't recovered from last year's dry season and soil moisture levels remained low.
The Ministry for Primary Industries has already begun advising farmers, encouraging them to monitor seasonal forecasts, and talk to bank managers, accountants, vets, professional advisers, and peers who have experienced previous El Nino events.
"The message from us is to be prepared for the worst and hope that the worst doesn't eventuate," said Katie Milne, Federated Farmers' adverse events spokeswoman.
Where she farms, on the South Island's west coast, El Nino typically brought the opposite situation to drought-prone areas in eastern parts of the country.
It meant significant damage to pastures from too much rainfall, and it was also harder for stock to thrive in the constant wet.
As expected, the 2015 El Nino is now close to its peak intensity in the tropical Pacific Ocean, recently reaching comparable levels in the tropics to the major 1982/83 and 1997/98 events.
What happened in the last big one?
In 1997, it became much drier than normal in the east from as early as July, with drought areas particularly pronounced from the Bay of Plenty down to Canterbury over the following summer.
In the Tararua town of Dannevirke, farmers remarked at having never experienced anything as devastating.
In late April 1998, the Ministry of Agriculture and Forestry estimated the likely cost of the drought on farm gate returns would be $256 million for the year ending June 30, 1998, and $169 million for the following year, giving a total of $425 million.
Given the impact on downstream value-added agricultural production, the likely total cost to the country was likely to be in excess of $1 billion.
MetService meteorologist Georgina Griffiths said farmers and growers were seeking information about what happened in that "super El Nino", and the one that preceded it in 1982/83, to get a handle on how bad it was last time.
However, she said, there was no guarantee that the climate in the first half of next year would unfold in the same manner as was seen in either of those summers.
The observed climate seen here during the 1982/83 and 1997/98 El Nino events differed over summer.
That of 1997/98 was strongly anticyclonic, with very high pressures over the North Island, and frequent west to northwest winds over the country, while in comparison, the summer of 1982/83 was stormy, with low pressures and frequent southwest winds over New Zealand.
Not surprisingly, summer 1997/98 was unusually hot and dry for many North Island and eastern regions, while summer 1982/83 was unseasonably cold across the country.
However, northern and eastern areas of both islands recorded dry summers in both events, often with less than 50 per cent of summer rain observed. Wellington was also rather dry, Ms Griffiths said, and the southwest of the North Island was in somewhat better shape, with closer to normal rainfall through summer and autumn.
"Importantly, the largest deviation seen during El Nino summers occurred in the regions that could least afford it."
Hardest hit were the Bay of Plenty, Taupo, Gisborne, Hawkes Bay and Wairarapa, Blenheim and Canterbury.
Notably also, large differences were seen in autumn rainfall between the events.
While autumn 1983 saw healthy rains return across the South Island, it remained drier in the northeast of the country.
In comparison, autumn 1998 was relatively dry across the entire North Island, particularly so for the east coast, and the eastern South Island also continued somewhat drier, too.
"The prolonged dryness through autumn 1998 was effectively the straw that broke the camel's back," she said.
"The autumn of 2016 may well be critical, too."
Ms Milne said that, whatever happened, all farmers were going into the New Year with eyes open.
"Our fingers are crossed that it's not terminal for too many of us - but it may be for a few."
1
What, exactly, is an El Nino pattern, how is one typically created, and how does it differ from a La Nina phase?
In the equatorial Pacific, an El Nino pattern is characterised by warmer than normal sea surface temperatures between South America and the International Dateline, warmer sub-surface temperatures, weaker easterly trade winds, lower air pressure in the central-eastern Pacific (Tahiti) and higher pressures over northern Australia (Darwin), and an eastward shift in rainfall patterns from the Indonesian region to near or east of the dateline. The La Nina pattern is essentially the opposite.
El Nino events can be initiated by random fluctuations in the trade winds, which produce low frequency sub-surface waves in the ocean and a feedback between the atmosphere and ocean changes that reinforces one extreme of the oscillation.
2 Just what kind of impact does it have on New Zealand's climate system - over and above normal seasonal patterns - and how do these effects vary around different parts of New Zealand?
The weaker easterly trade winds in the Pacific coincide with higher pressures over Australia, and stronger or more persistent southwesterly winds over New Zealand.
In turn, these wind anomalies lead to generally cooler than normal temperatures locally, and reduced rainfall in the more sheltered east and northeast regions.
3 As climatologists, how have you gone about forecasting the severity of this current El Nino?
Climatologists use a variety of mathematical models. At the present time, there is unanimity among these models that the current event, measured by a sea temperature metric, is one of the four strongest in the past 50 years and should intensify further to peak in about January 2016.
4 Niwa scientists have held talks with farmers about this El Nino. What's the message to them, and where and how might farmers be hardest hit this summer?
There are a number of key messages. From the climatological viewpoint, it is clear that a very strong El Nino is already present in the Pacific, it is forecast to continue - and strengthen - over the coming months, the expected southwesterly pattern of winds over New Zealand is already in place, and the expected dry conditions in the east over summer are highly likely.
From a practical perspective, it is important that farmers don't panic, that they monitor the situation carefully - the Niwa forecasts plus conditions on their own farm - and that they have an action plan that is implemented if a severe drought does eventuate at their location.
5 There are pockets in parts of the country where soils remain dry and still haven't recovered from last summer's drought. How concerning is it that the lack of moisture will be compounded with the effects of El Nino?
Obviously, this is a concern.
There are two locations where this is the case: in north Canterbury between Christchurch and Cheviot, and in South Canterbury/North Otago inland from Oamaru.
Other regions that have shown a strong drying trend since winter include Tasman-Marlborough, southern Wairarapa and the Bay of Plenty.
6 What other negative impacts might we expect? And can we assume fire danger in many parts of the country will be at much higher risk?
Apart from drought, there will be a higher risk from fires in eastern regions because of a combination of drier conditions and stronger winds.
Urban water supplies in eastern regions will also need to be closely monitored by local councils.
7 This El Nino is being compared to the 1997/98 El Nino, which cost the economy hundreds of millions of dollars and brought about a horror drought. What exactly happened in that El Nino, and how might this one compare?
Each El Nino drought tends to be a little different, but there are common features, especially with the stronger ones.
In the case of the 1997/98 El Nino, many eastern parts from Northland down to mid-Canterbury received less than 50 per cent of the normal summer rainfall. On the other hand, many western regions received near normal or above normal rainfall over the summer.
One mitigating factor with the 2015/16 El Nino is that the message has got out to farmers, and they are probably much better prepared this time around. Some farmers have been proactive, planting deeper-rooting grasses or building water storage facilities.
8 What will the El Nino mean for city-dwellers?
The summer is expected to be cooler and windier than normal in many locations, and drier in the eastern cities and towns, from eastern Northland down to Canterbury.
City dwellers may welcome more sun - and less rain - but water restrictions could bite earlier than usual or last longer.
9 As an El Nino is a global phenomenon, what New Zealand will experience will form a small part of a much bigger picture. What are expected to be its biggest impacts elsewhere on the planet?
Likely impacts include: drought in eastern Australia and higher wildfire risk, lower rainfall in islands of the southern sub-tropical Pacific (Samoa, Fiji, Tonga, southern Cook Islands) and higher rainfall for islands further north (Tuvalu, northern Cook Islands, Tokelau, Kiribati), higher rainfall - perhaps floods - in parts of Peru and Chile, lower rainfall in coffee-growing areas of northeast Brazil, a weaker summer monsoon in India, and assorted impacts elsewhere.
10 Some climate researchers have suggested the frequency and intensity of El Nino will be affected by climate change. Is this true?
There has been a lot of research into what the global climate models predict for future El Nino events. However, results are far from consistent or convincing about the direction of change; the only thing we can be sure of is that El Ninos will continue to occur.
Other changes associated with global warming - such as higher temperatures and evaporation rates and more water carried by the atmosphere - may well amplify local El Nino impacts, even if the event in the equatorial Pacific is of similar strength to present-day events.
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