What La Niña is

La Niña is the cool phase of the El Niño–Southern Oscillation. Where El Niño is the trade winds giving way, La Niña is the same winds blowing harder than usual. They push more warm surface water into the western Pacific and draw more cold water up along the South American coast, so the central and eastern tropical Pacific run colder than normal and the Pacific’s rainfall concentrates further west. NOAA declares La Niña conditions when the Oceanic Niño Index reaches −0.5 °C.

For New Zealand the practical difference is wind direction. La Niña favours north-easterlies, which arrive warm and carrying tropical moisture, rather than the westerlies and south-westerlies of an El Niño summer. The name is simply the counterpart to the older one — la niña, the girl, set against el niño.

How it works

Stronger trade winds drag more surface water westward along the equator. Warm water banks up around Indonesia and northern Australia, deepening the pool of warmth already sitting there, while the water drawn up to replace it off South America comes from further down and colder. The temperature contrast across the Pacific sharpens rather than flattening.

Storms follow the warm water, so tropical rainfall packs into the western Pacific. That is why the cold phase floods eastern Australia and Indonesia while drying Peru and the southern United States — close to a mirror of what El Niño does to the same places. It also lowers wind shear over the Atlantic, which is why Atlantic hurricane seasons tend to be busier during La Niña.

The cold phase tends to outlast the warm one. Warm water displaced westward has to make its way back before conditions can neutralise, and the process often stalls, leaving the Pacific cold for a second or third year. Multi-year La Niña events are ordinary in the record; multi-year El Niño events are close to unknown.

What La Niña means for New Zealand

NIWA describes La Niña as bringing more frequent north-easterly winds. Those winds carry moist air down from the tropics, so the north-east of the North Island tends to be wetter and more humid, while the lower and western South Island tends to be drier. Temperatures are usually warmer than normal across much of the country, with regional and seasonal exceptions. The odds of an ex-tropical cyclone reaching New Zealand also rise, because cyclone activity in the South Pacific shifts west towards the Coral Sea and the Tasman.

The same qualification applies here as to the warm phase: on NIWA’s figures, ENSO accounts for less than 25 percent of the year-to-year variance in seasonal rainfall and temperature at most New Zealand locations. It shifts the odds across a season rather than setting the weather on any given day.

RegionRainfall leanNotes
NorthlandWetterDirectly exposed to the moist north-easterly flow; humid, and the most likely landfall region for ex-tropical cyclones.
AucklandWetterAbove-normal rainfall is the usual lean. The January 2023 Anniversary floods fell in a La Niña summer.
Bay of PlentyWetterOne of the wettest regions in the cold phase — open to the north-east.
GisborneWetterExposed to north-easterlies and to ex-tropical systems tracking down the east coast.
Hawke's BayWetterThe reverse of its El Niño lean; Cyclone Gabrielle struck here in February 2023.
WaikatoMixedWetter than normal in a strong event, though less reliably than the regions further north-east.
TaranakiMixedWest-facing, so it misses much of the north-easterly flow.
Manawatū-WhanganuiMixedNo strong signal either way; warmer than normal is the more reliable lean.
WellingtonMixedLess wind than an El Niño summer, with rainfall near normal.
NelsonMixedSheltered from the north-east; temperature is the clearer signal.
TasmanMixedNear normal rainfall, warmer than usual.
MarlboroughMixedNear normal, and warmer — a contrast with its dry El Niño lean.
CanterburyMixedFewer nor'westers than in an El Niño summer, with rainfall near normal.
OtagoDrierPart of the lower South Island that dries in the cold phase.
SouthlandDrierReduced rainfall — the reverse of its El Niño lean.
West CoastDrierLess westerly flow means less orographic rain over the Alps.
Chatham IslandsNo clear signalNo consistent ENSO rainfall signal this far east.

Leans are the tendency across past La Niña events, not a forecast for a particular season. Source: NIWA — The impact of El Niño and La Niña on New Zealand's climate

The 2020–23 event, and early 2023 in New Zealand

The most consequential La Niña for New Zealand in decades was not a particularly strong one. It peaked at −1.06 °C, well short of 1973 or 1988. What set it apart was its length: three southern summers in a row in the cold phase, the first three-year La Niña of this century.

Over that time the Tasman Sea and Coral Sea stayed unusually warm, which kept the air arriving over northern New Zealand loaded with moisture. The Auckland Anniversary floods in late January 2023 and Cyclone Gabrielle in February both fell in the closing months of the event. NIWA associates that flooding with the La Niña phase, together with the warm Coral Sea and a favourable pulse of the Madden–Julian Oscillation, which supplied the heat and moisture those systems drew on.

A common mix-up. Those events are often attributed to El Niño, because El Niño dominated the news later that year. NIWA did not declare El Niño conditions until September 2023 — seven months after Gabrielle. Heavy rain in the warm, humid north-east fits the La Niña pattern; El Niño tends to dry those same regions out.

Source: NIWA — El Niño and La Niña

Every La Niña since 1950

The blue bars below the line are La Niña years. Two things stand out against the warm phase: the cold phase reaches a shallower extreme, and it repeats. Runs of two and three consecutive years are common in the record, where back-to-back El Niño years are almost unknown.

What past La Niña events did

As with the warm phase, these seasons are described as La Niña contributing to what happened rather than causing it.

1973–76

Peak ONI −2.0 °C · NDJ 1973 · multi-year

The deepest La Niña in the record that begins in 1950, and a long one — the Pacific stayed cold through three southern summers with only a brief break. It followed directly on the 1972–73 El Niño, the pattern of a strong warm event tipping into a strong cold one.

Australia
Two of the wettest years on record across the east, with widespread flooding, including the Brisbane flood of January 1974.
Peru
Strengthened upwelling returned cold, nutrient-rich water to the coast and the anchoveta fishery recovered from its collapse during the preceding El Niño.
New Zealand
Warmer and more humid summers in the north, with the north-easterly flow that typifies the cold phase here well established.

1988–89

Peak ONI −1.9 °C · NDJ 1988

A short, sharp event and the second-strongest measured. It began during one of the most damaging droughts in modern United States history.

United States
The 1988 drought and heatwave across the Midwest and Great Plains, one of the costliest weather events in the country's history.
Atlantic
An active hurricane season — La Niña reduces the wind shear that otherwise tears storms apart, so Atlantic activity tends to rise.
Bangladesh
Severe monsoon flooding covering a large share of the country.
New Zealand
A warm summer, with rainfall leaning above normal in the north and east of the North Island.

2010–12

Peak ONI −1.5 °C · NDJ 2010 · multi-year

A strong double-dip event, and the clearest demonstration of how much water La Niña moves from ocean to land. So much rain fell over Australia, South America and South-East Asia that global sea level measurably dipped for about a year before recovering.

Australia
The 2010–11 Queensland floods, including the Brisbane flood of January 2011, during one of the country's wettest periods on record.
Horn of Africa
Failed rains and severe drought across Somalia, Kenya and Ethiopia through 2011 — the cold phase dries the eastern Horn where the warm phase floods it.
United States
Drought across Texas and the southern plains.
New Zealand
Warm, humid summers. The 2010–11 season was among the warmer ones on record at the time, with above-normal rainfall in northern and eastern areas.

2020–23

Peak ONI −1.1 °C · NDJ 2020 · multi-year

Never especially deep, but rare in shape: three southern summers in a row in the cold phase, the first three-year La Niña of this century. Its length mattered more than its strength — the Tasman Sea and Coral Sea stayed unusually warm throughout, which loaded the atmosphere around New Zealand with moisture.

Eastern Australia
Repeated flooding across New South Wales and Queensland through 2021 and 2022, including the Northern Rivers floods of early 2022.
Horn of Africa
Five consecutive failed rainy seasons by 2022, the region's worst drought in decades.
United States
Sustained drought across the south-west, with Colorado River reservoirs falling to record lows.
New Zealand
The most consequential La Niña here in decades. NIWA associates the flooding in the north and east of the North Island in early 2023 — the Auckland Anniversary floods in late January and Cyclone Gabrielle in February — with this La Niña phase, alongside unusually warm water in the Coral Sea and a favourable pulse of the Madden–Julian Oscillation. El Niño was not declared until September 2023, months after both events.

Impact summaries draw on the World Meteorological Organization’s event reporting, NOAA’s historical ENSO record and NIWA’s New Zealand climate summaries. Source: WMO, NOAA and NIWA

Common questions

What is La Niña?

La Niña is the cool phase of the El Niño–Southern Oscillation. The trade winds along the equator strengthen beyond normal, pushing more warm surface water west and drawing more cold water up along the South American coast. The central and eastern tropical Pacific cools, and rainfall concentrates further west than usual. NOAA declares La Niña conditions when the Oceanic Niño Index reaches −0.5 °C.

What does La Niña mean for New Zealand?

NIWA describes La Niña as bringing more north-easterly winds than normal. That draws moist air down from the tropics, so the north-east of the North Island — Northland, Auckland, Bay of Plenty, Gisborne and Hawke's Bay — tends to be wetter and more humid, while the lower and western South Island tends to be drier. Temperatures are usually warmer than normal over much of the country. The risk of an ex-tropical cyclone reaching New Zealand is also higher.

Is La Niña worse than El Niño for New Zealand?

They carry different risks rather than one being worse. El Niño's signature problem here is drought in the east and north, as in 1997–98. La Niña's is heavy rain and flooding in the north and east of the North Island, and a greater chance of an ex-tropical cyclone arriving — the Auckland Anniversary floods and Cyclone Gabrielle both happened in the closing months of the 2020–23 La Niña. Which matters more depends entirely on where you are and what you do.

How long does La Niña last?

Usually about a year, but the cold phase runs long more often than the warm phase does. Multi-year La Niña events are common in the record, and the 2020–23 event lasted three southern summers in a row — the first three-year La Niña of this century. El Niño events almost never repeat like that.

Does La Niña mean more cyclones for New Zealand?

It raises the odds. La Niña shifts tropical cyclone activity in the South Pacific further west, closer to the Coral Sea and the Tasman, and warmer seas around northern New Zealand give any system that tracks south more energy and moisture to work with. That is a shift in probability across a season, not a forecast of any particular storm.

More on New Zealand’s climate patterns

El Niño

The warm phase — how it works, what past events did worldwide, and the regional pattern for New Zealand, with the current Pacific figures.

El Niño vs La Niña

The two phases side by side: what differs, how often each occurs, and which one the Pacific is in right now.

Sources