Brace yourselves, because the weather gods are stirring up a complex brew for the upcoming season! The latest Seasonal Climate Outlook for March to May 2026 reveals a fascinating dance of oceanic and atmospheric forces that will shape New Zealand's weather in the coming months. But here's where it gets controversial: while the transition to ENSO-neutral conditions seems clear, the lingering effects of La Niña and the emergence of a 'coastal El Niño' could throw some unexpected curveballs our way.
Outlook Summary: Unraveling the Weather Puzzle
The coupled ocean-atmosphere system has officially shifted to ENSO-neutral (neither La Niña nor El Niño) as of February 2026. However, remnants of La Niña-like circulations are expected to persist, potentially steering rain-bearing systems from the north. The Relative Oceanic Niño Index (RONI) weakened to –0.67°C in February, falling just shy of the La Niña threshold of –0.7°C. Meanwhile, subsurface temperature anomalies are breaking free from their previous La Niña patterns, and a sharp rise in Sea Surface Temperatures (SSTs) along South America’s coast signals a short-lived ‘coastal El Niño.’
And this is the part most people miss: Despite the 95% chance of ENSO-neutral conditions dominating the Tropical Pacific through May 2026, the odds of El Niño developing by winter are growing. This dual narrative—neutral now, but El Niño later—sets the stage for a dynamic and potentially unpredictable season.
What’s in Store for New Zealand?
For the next three months, New Zealand’s atmospheric circulation will feature high pressure to the south and low pressure to the north, creating an easterly flow anomaly. Autumn kicks off with anticyclonic conditions, but tropical incursions could disrupt the calm from mid-March, bringing unsettled weather. While high pressure is likely to restore order, another rainmaker from the north could arrive by late March or early April.
Looking further ahead, the north remains the primary source of significant weather through April and May. Southern Ocean systems may become less frequent, and the South Island could enjoy prolonged periods of settled weather. However, the Tropical Cyclone Outlook warns of a normal to elevated risk of ex-tropical cyclone interactions, especially as we enter the peak climatological risk period.
Temperature and Rainfall: A Tale of Contrasts
Seasonal temperatures are expected to be above average in the north and west of the North Island, near average elsewhere, with the west of the South Island potentially leaning above average. Rainfall, however, tells a more varied story. The north and east of the North Island are likely to see above-normal rainfall, while the west of the South Island could experience below-normal levels. Tropical-influenced systems may bring significant rainfall to parts of the North Island, particularly in March and April.
Regional Predictions: Breaking It Down
Here’s a closer look at regional forecasts, with probabilities for temperature, rainfall, soil moisture, and river flows:
Northland, Auckland, Waikato, Bay of Plenty
- Temperatures: Above average (55% chance).
- Rainfall: Above normal (45% chance), with potential heavy rainfall from tropical systems.
- Soil moisture: Below normal (45% chance).
- River flows: Below normal or near normal (40% each).
- Temperatures: Above average (55% chance).
Central North Island, Taranaki, Whanganui, Manawatu, Wellington
- Temperatures: Above average (50% chance).
- Rainfall: Above normal or near normal (40% and 35% chance, respectively).
- Soil moisture and river flows: Near normal (40% chance), with notable forecast uncertainty.
- Temperatures: Above average (50% chance).
Gisborne, Hawke’s Bay, Wairarapa
- Temperatures: Near average (45% chance).
- Rainfall: Above normal (50% chance), with heavy rainfall possible from tropical systems.
- Soil moisture and river flows: Above normal or near normal (40% each).
- Temperatures: Near average (45% chance).
Tasman, Nelson, Marlborough, Buller
- Temperatures: Near average (45% chance).
- Rainfall: Near normal (40% chance), with forecast uncertainty.
- Soil moisture and river flows: Near normal or below normal (40% and 35% chance, respectively).
- Temperatures: Near average (45% chance).
West Coast, Southern Alps, Inland Otago, Southland
- Temperatures: Above average or near average (45% and 40% chance, respectively).
- Rainfall: Below normal (50% chance).
- Soil moisture: Near normal (45% chance).
- River flows: Below normal or near normal (40% each).
- Temperatures: Above average or near average (45% and 40% chance, respectively).
Coastal Canterbury, East Otago
- Temperatures: Near average (45% chance).
- Rainfall: Above normal or near normal (40% and 45% chance, respectively).
- Soil moisture and river flows: Near normal (45% chance).
- Temperatures: Near average (45% chance).
The Bigger Picture: Oceanic Forces at Play
Sea surface temperatures in the central equatorial Pacific, as measured by the RONI, weakened significantly in February but no longer meet La Niña criteria. The emergence of a ‘coastal El Niño’ off South America adds another layer of complexity. While some coastal El Niño events precede basin-wide El Niño, others remain localized.
Subsurface ocean temperatures in the Pacific continue to warm, contributing to the decay of La Niña signals. Positive upper-ocean heat content anomalies have expanded eastward, consistent with the transition to ENSO-neutral conditions. Forecasts indicate a 95% chance of these conditions persisting through May, with global models increasingly pointing toward El Niño later in 2026.
Controversial Question: Are We Underestimating the Impact of Coastal El Niño?
While the focus remains on ENSO-neutral conditions, the development of a coastal El Niño raises questions. Could this localized warming have broader implications for New Zealand’s weather, or is it a mere blip in the larger climate narrative? Share your thoughts in the comments—this is a debate worth having!
Forecast Confidence: Temperatures vs. Rainfall
Confidence in temperature forecasts is medium, with onshore airflows moderating eastern temperatures and western areas potentially warming. Rainfall forecasts, however, remain low to medium due to the unpredictable nature of northern rainmakers and their ‘boom or bust’ pattern.
Final Thoughts
As we navigate this intricate weather tapestry, one thing is clear: the next few months will be a fascinating study in contrasts. From lingering La Niña echoes to the emergence of El Niño whispers, New Zealand’s climate is anything but boring. Stay tuned, stay informed, and let’s weather this together!
