Earth Sciences New Zealand (ESNZ) forecasting principal scientist Chris Brandolino said there would be increased potential for drought conditions if El Nino continued through spring and into summer.
The latest ESNZ three-month outlook (May-July 2026) showed temperatures in eastern parts of Otago were about equally likely to be near average or below average, but the usually dry rainfall totals, soil moisture levels and river flows might be even lower than usual, he said.
Temperatures on the West Coast, the Southern Alps and foothills, inland Otago and Southland were also equally likely to be near average or below average, he said.
But rainfall totals were equally likely to be near normal or above normal, and soil moisture levels and river flows were most likely to be near normal.
‘‘Occasional cold snaps are possible, especially under persistent high pressure where fog, frost and cold night-time temperatures could occur.
‘‘We’ll need to watch for that when high pressure sticks around.’’
Mr Brandolino said there was a 65% chance El Nino conditions would form during this three-month period and they were expected to peak in summer 2026-27.
‘‘Neutral El Nino Southern Oscillation (Enso) conditions are present in the tropical Pacific.
‘‘However, the coupled ocean-atmosphere system is showing signs of a rapid transition toward a ‘significant’ El Nino event — potentially comparable to some of the strongest El Nino events on record.’’
El Nino and La Nina are the two phases of Enso — a natural climate cycle driven by ocean temperatures and atmospheric pressure across the tropical Pacific.
During El Nino, warmer-than-average ocean temperatures develop in the central and eastern Pacific, weakening the trade winds and shifting tropical rainfall towards the central and eastern Pacific.
Downstream of the circulation changes in the tropics, El Nino has the ability to shape weather in New Zealand by influencing where areas of high pressure sit over the country.
Those high pressure systems tended to cause a cooler southwesterly flow over New Zealand, which usually brought increased rainfall to Southland, inland parts of Otago and western-facing areas of the South Island.
However, it also brought reduced rainfall for eastern areas, including Dunedin and Oamaru.
‘‘The risk of drier-than-normal conditions is expected to increase as the season progresses,’’ he said.
‘‘Peak El Nino conditions are expected to occur during the austral summer of 2026-2027, with the potential for this event to have significant impacts.’’
