A ‘‘significant’’ El Nino event is expected to arrive this winter (June to August 2026), bringing increasingly undesirable weather for much of the southern region.
However, the same weather phenomenon was expected to bring drier and warmer-than-average conditions to eastern Otago areas.
ESNZ forecasting principal scientist Chris Brandolino said as the winter season progressed, air flow patterns were expected to tend towards a west or southwesterly flow, which was characteristic of El Nino conditions.
El Nino and La Nina are the two phases of the El Nino-Southern Oscillation (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, shifting tropical rainfall towards there and weakening the trade winds.
El Nino’s impacts would extend downstream of the circulation changes in the tropics and would shape weather in New Zealand.
‘‘The coupled ocean-atmosphere system continues to transition rapidly toward El Nino.
‘‘Warm subsurface ocean temperature anomalies have continued to intensify and expand in the tropical Pacific, consistent with the ongoing transition toward El Nino and raising the potential for a significant event.’’
Mr Brandolino said on the West Coast, Southern Alps and foothills, inland Otago, and Southland, temperatures were about equally likely to be below average or near average; rainfall totals were likely to be above normal or near normal; and soil moisture levels and river flows were most likely to be near normal.
‘‘Chances for active weather - like heavy rain and strong winds - are expected to increase later in the winter season.’’
Along eastern Otago, he said temperatures were about equally likely to be near average or above average.
However, he said it was likely there would be increased temperature variability - large temperature swings and unusually windy periods - later in the winter season.
Rainfall totals were most likely to be below normal and soil moisture levels and river flows were about equally likely to be near normal or below normal.
‘‘The prospect of below normal winter rainfall in several regions is likely to translate to below-normal groundwater recharge, creating challenges for water-reliant sectors.
‘‘El Nino–related influences on regional weather patterns are expected to become more apparent later in the season as Enso signals strengthen.
‘‘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,’’ he said.
