You could be forgiven for asking what the heck is going on.
Hurricane-force winds shrieking across the Wairarapa coast and the Southern Alps, within a hair’s breadth of setting a New Zealand record wind speed.
Thunder, lightning and hail plaguing Otago, gales and severe turbulence cancelling flights.
Scrub fires burning and heat from a Sydney heatwave bringing record September temperatures in the mid- to high-20s in parts of Canterbury and Otago this week — when daily maxima in this neck of the woods in mid-September should normally be 13-14degC.
Being a law unto itself, the weather has now done a complete about-turn, with cold southerly rain and low snow falling up the South Island’s east coast.
Meteorologists say frequent cool changes are still likely as we go through spring. But the broader picture is of longer spells of hot, windy and dry conditions in the months ahead.
It’s almost like someone has left the back gate open, letting all this stuff blow in.
Welcome to El Nino 2023-24.
Today is the spring equinox — when the hours of daylight and darkness are the same. From tomorrow, daylight dominates over night-time, and we start heading towards our long southern summer twilights.
There’s nothing particularly unusual about the westerly winds that have been buffeting us recently. They are, after all, the dominant wind and weather pattern at this time of year.
Battling airmasses from the subtropics and the subantarctic vie for supremacy during September and October especially, bringing spells of tempestuous weather — nearly always windy, often stormy, alternately warm and dry and freezing cold and even snowy.
We don’t need an El Nino to bring the westerly winds, but when there is one it tends to supercharge them.
This spring’s El Nino is perhaps so well-signalled because it comes after the rarity of three consecutive La Ninas.
La Nina is the opposite of El Nino, bringing more subtropical, rainy northeasterly flows to the north and east of much of the country down to about Banks Peninsula, and weakening the grip of the westerlies.
The concern this spring and summer is that, unlike in most years, the westerlies will keep blowing beyond November and persist into autumn next year, desiccating soils and crops east of the ranges in the South and North islands, frequently propelling temperatures well into the 30s and providing plenty of fuel for wildfires.
It’s a different story west of the Southern Alps and in Southland, where El Nino generally brings cold, windy, squally weather, with intense and often damaging rainfalls along the West Coast.
For those whose livelihoods depend on the weather and the land, be they farmers or foresters, Fire and Emergency New Zealand or electricity generators, early warning of El Nino is vital.
But like everything to do with the planet, what El Nino may or may not do is not quite that simple.
Each El Nino has its own particular personality, influenced by other large-scale climate patterns with impressive names, such as the Madden-Julian Oscillation, the Indian Ocean Dipole and the Southern Annular Mode.
Two of the strongest El Ninos on record delivered totally different weather to the eastern South Island.
The 1982-83 event brought a summer with constant cold southwesterly changes, frequent thunder and lightning, heavy hailstorms and even a tornado at Halswell on the outskirts of Christchurch.
However, the 1997-98 event generated the opposite — a hot, dry summer with gusty northwesterlies, crippling drought from Marlborough down to Central Otago and dozens of afternoons in the mid-30s lasting into late March.
Both might have initially looked like they would be similar, with unrelenting westerly winds. But just a few compass degrees on either side of west made a huge difference.
It is a challenge for meteorologists to know which way El Nino might go this summer. Could this be the year the Otago record high temperature of 38.7degC set in Alexandra on February 5, 2005 and recorded again on January 30, 2018, gets surpassed? Is the nationwide record of 42.4degC in Rangiora on February 7, 1973 under threat?
Is what we have had this past week a glimpse of what’s to come, a test pot of colour thrown on the wall?
Or will this El Nino have its own plans, and spring us a few surprises?
Earlier this week, the last piece in the El Nino jigsaw puzzle finally fell into place.
While much of the meteorological world had been talking about El Nino as a done deal, oddly the Bureau of Meteorology in Australia — the country often hardest hit by its heat and drought — had appeared to be dragging its heels in declaring one.
That changed on Tuesday evening, when the bureau finally shifted its pointer from "El Nino Alert" to "El Nino".
"There’s quite a lot of time to play out between now and the start of summer and when we typically see the peak impacts from El Nino. But we have been seeing the warmest seas relative to average consolidating near the west coast of South America, and what that suggests is the flavour of this El Nino looks to be like the classical events, which we haven’t had in some time, the kind of ’97-’98 or ’82-’83 event."
Computer guidance is showing an event with warmer west to northwest, rather than cooler west to southwest winds, he says.
"But every El Nino has its own twists and turns. That last El Nino, the 2015-16 event, was tracking quite dry in November and especially December, and there were certainly some concerns about drought. And then in January, a moist northwesterly flow took hold, and that brought down good moisture that kind of erased some of those soil moisture deficits.
"When we look at this event, you wonder what’s something that could generate an unusual twist or turn. You look at the whole big picture of the globe right now and sea temperatures are, you know, at record levels, and so how does the El Nino signal interact with that?
"So, you know for that reason alone it is not going to produce the same thing that we saw in
’97-’98 or ’82-’83. The context of El Nino in a changing climate is an important factor to consider in forecasting," Noll says.
WeatherWatch head forecaster Philip Duncan says more of the weather this summer will be coming out of a heated-up Australia.
"I like to look backwards to look forward, and the weather pattern we’ve seen over the last three, four months has been encouraging a lot of airflow out of Aussie. That makes me feel like we’re going to be having a warmer-than-average rest of the year.
"I think we were the only forecaster this year to say winter would be warmer-than-average. The others were saying it’s going to be cold.
"I remember thinking, ‘El Nino is not made in a laboratory with your white lab coat on’. It’s chaotic, messy, and everything’s been leaning warmer, so why would this suddenly change when it encourages more sideways westerlies rather than southerlies?"
Even the southerlies that have arrived have been quickly "washed away" by milder westerlies, Duncan says.
"What we’ve been saying to farmers is that, even if the ground is muddy at the moment, you need to be thinking about water conservation for the end of the year.
"Also that there is a silver lining, at the moment anyway, that we are seeing some rainmakers still coming through in the months ahead. And so even if it leans a bit drier, it’s not necessarily leaning extremely dry for all regions. But I wouldn’t extend that out to 2024, with January kicking off in El Nino’s peak."
That summer, Oamaru was even drier than the country’s traditionally driest spot, Alexandra. Niwa records show Oamaru had just 64mm of rain in the three months (although five days of data are missing), compared with Alexandra’s 108mm (with four days missing).
The pages of the ODT in January and February 1998 were full of stories of extreme fire risk for inland Otago, bans on irrigation, other water restrictions, dried up rivers, grim warnings of no significant rain until winter, drought relief packages, sizzling temperatures, albatrosses at Taiaroa Head dying from heat stress, and regions on the "brink of disaster".
Relief from rain was slow to come, and the drought only finally broke in March 1999, after 19 months of below normal rainfall across Otago. Estimates of the cost of that El Nino were around $1 billion, or more than 1% of gross domestic product.
Federated Farmers adverse events spokeswoman Sandra Faulkner told The Weekend Mix "we don’t need it going really dry", particularly for farmers in the east of the North Island still coping with the aftermath of Cyclone Gabrielle.
She says support is there for farmers from various sources if this El Nino brings drought.
"There’s plenty of information available for farmers. The message from us is to make sure you use all the tools available and that we are always here to speak to. Always make sure you have the best team around you too — your bank manager, agronomists, stock agents, Beef+Lamb, DairyNZ."
The Ministry of Primary Industries has been working with Niwa and has invested more than $100,000 in developing and trialling a drought forecasting tool that uses innovative climate modelling.
MPI director of rural communities and farming support, Nick Story, says Niwa’s drought monitoring and forecasting models will be crucial as farmers prepare for the summer.
"It’s a pretty impressive tool. The live pilot has been available since February for people to view drier (and wetter) conditions out to 35 days, and with greatly increased precision on local forecasts. This will support farmers and growers with better information to make early decisions."
Preparing for drought and other adverse weather events is a regular part of farmer and grower seasonal business planning. MPI has been carrying out monthly national feed surveys since March, Story says.
"Farmers and growers are encouraged to plan and prepare ahead of drought to reduce the impacts, to talk to experts at their bank and with financial advisers, vets, industry organisations and peers who have gone through an El Nino or dry spell before.
"They should also look out for, and get support from, neighbours, families and friends. Organisations, such as the Rural Support Trust, may also provide more community events to get people off farm and connecting."
If a drought causes significant effects, MPI can consider various forms of support and works with other agencies, including Inland Revenue and Work and Income, he says.
Farmers had been well prepared for the 2015-16 El Nino. Livestock farmers were encouraged to destock early to reduce feed demand on farm, conserve feed, arrange for grazing elsewhere or bring in supplementary feed from not-so-dry areas.
"In an El Nino, drier weather may start earlier than usual and extend further into autumn. Water restrictions may be needed and crops and stock might be compromised by soil moisture deficits and heat stress, and an increased risk of fungal diseases.
"However, some sectors, including those producing wine and fruit, may even benefit from longer spells of dry weather, provided there is water when most needed," Story says.
The threat of a long and possibly extreme wildfire season sparked a very early call from FENZ more than a week ago to ban unpermitted fires throughout Central Otago and the Upper Waitaki district.
That decision was a month earlier than usual and partly based on a daily fire-severity rating in Cromwell already more than double the 17-year average for this time of the season, and well above where it was at the start of 2015-16 event.
Fires are already breaking out. On Wednesday afternoon, State Highway 1 at Hook about 1km north of the Waimate turnoff was closed by smoke whipped up in strong nor’westers from a nearby vegetation fire.
The same night, people in half a dozen houses were evacuated due to a large scrub blaze near Twizel, which required helicopters to help staunch the flames.
A hotter summer than normal may also mean extra pressure on electricity generation to cope with an increase in air-conditioning use. Peak loads in New Zealand have traditionally been in winter, but a warming climate means summer demand is likely to rise too.
Meridian Energy head of wholesale operations, Chris Garr, says the company relies on forecasts from Niwa and MetService to make generation decisions.
"This ranges from detailed short-term precipitation, inflow and wind forecasts for our generation assets, to more generalised climatic outlooks that provide more generic indicators of medium-term weather."
A strong El Nino typically means wetter conditions in the lower South Island, more so in the Waiau catchment than the Waitaki catchment. But there have been both very wet and very dry periods during past El Ninos, he says.
"There is no guarantee conditions will be wet and still a reasonable probability of below- average inflows. These forecasts do not remove the typical uncertainty we face with weather forecasts, but they do provide a direction.
"The impact on wind generation is less understood. A stronger El Nino usually means more wind in the lower North Island, but again there is still a wide range of outcomes possible."
Hydro-lake storage was above average heading into spring, Garr says.
"With an average snowpack and a forecast El Nino event, we anticipate this will allow us to generate a little more than normal over the summer months and/or carry a little more storage through to next autumn and winter."
El Nino can also affect those whose lives are spent trying to predict it and its effects.
MetService head of weather communication Lisa Murray says the influence of any specific El Nino on New Zealand’s weather is always different.
"This does not look like a typical El Nino summer, with some wet weather in the mix with the heat, wind and dryness. However, the intermittent rainfall in eastern areas of the country won’t be enough to keep the soil moisture at a good level for farmers and growers."
WeatherWatch’s Duncan says these broad-scale events change his forecasting approach.
"You look at the weather patterns differently from in a neutral season. It massively ups the game. Farmers and growers demand more detail than the mainstream headlines which just say hot, dry weather to come.
"This El Nino does look serious. Eastern areas are already noticing the drier change. But we need to remember it doesn’t just roll out like explained in a textbook.
"For us, halfway between the tropics and the Antarctic, El Nino can be much more of a wildcard."
What is El Nino?
El Nino is driven by sea-surface temperature changes around the Pacific Ocean, with water becoming warmer than average in the central-eastern equatorial Pacific. This in turn affects atmospheric circulation. Its intensity in the atmosphere is measured by the Southern Oscillation Index, which is the difference in average air pressure between Tahiti and Darwin. In an El Nino, average pressures are lower in Tahiti, resulting in a negative value of the SOI. Persistent westerly winds are the main feature of South Island El Nino events, which generally means drier weather in the east and wetter weather on the West Coast and in the far south.
