Changing airflows mean changing weather from here till March and, to quote our principal forecaster Chris Brandolino, "La Nina hasn’t gone away". In short, it’s going to be mixed.

- There is an increased likelihood of more westerly quarter (SW to NW) winds than previously indicated. However, this pattern is expected to be interspersed with easterly quarter (SE to NE) air flows, especially during periods of La Niña-like weather.

- There is enhanced potential for rain events linked to the tropics and sub-tropics to impact the country from mid-January through to March. Apart from the west and east of the South Island, the rest of New Zealand has about equal chances for near normal or above normal rainfall for the coming three months.

- Areas not exposed to rain-bearing weather systems may experience extended dry spells, such as the first half of January, and sub-seasonal projections of rainfall and dryness are updated daily through the NIWA35 forecast.

- Air temperatures are likely to be above average for the North Island, with about equal chances for near average or above average seasonal temperatures for the South Island. The change in air flow patterns, as noted above, increases the odds for spells of cooler than usual summertime temperatures.

Regional outlooks and more details in the full report below, along with associated graphics.

NIWA Outlook: January – March 2025

Outlook Summary

• A La Niña Watch remains in effect.

• Recent sea surface temperature anomaly (SSTA) patterns in the tropical Pacific, while somewhat consistent with La Niña, present some unusual characteristics with maximum SSTA’s located in the central equatorial Pacific, and warmer than average sea surface temperatures in the far eastern tropical Pacific. This has likely contributed to atypical La Niña-like weather patterns to-date in the New Zealand region.

• In addition, international guidance for January – March 2025 indicates a reduction in the chance conventional La Niña thresholds will be met (about a 40% chance), while the probability for ENSO-neutral conditions to persist have increased (about a 60% chance) relative to prior forecasts.

• Consequently, there is an increased likelihood of more westerly quarter (SW to NW) winds than previously indicated. However, this pattern is expected to be interspersed with easterly quarter (SE to NE) air flows, especially during periods of La Niña-like weather.

• Despite reduced rainfall through about mid-January, there is enhanced potential for rain events linked to the tropics and sub-tropics to impact the country through March 2025. Thus, the risk of occasional heavy rain events remains distinctly possible, particularly as the season progresses. Apart from the west and east of the South Island, the rest of New Zealand has about equal chances for near normal or above normal rainfall for the coming three months.

• Areas not exposed to rain-bearing weather systems may experience extended dry spells, such as the first half of January, and sub-seasonal projections of rainfall and dryness are updated daily through the NIWA35 forecast.

• Air temperatures are likely to be above average for the North Island, with about equal chances for near average or above average seasonal temperatures for the South Island. The change in air flow patterns, as noted above, increases the odds for spells of cooler than usual summertime temperatures.

• Coastal sea surface temperatures (SSTs) ranged from about 0.8C to 1.6C above average around the country by the end of December, but marine heatwave conditions have receded in both extent and amplitude recently. Global climate forecasts are for SSTs to remain above average around New Zealand during the rest of summer. While marine heatwaves (MHW) remain possible over the coming three months, given the aforementioned change in air flow patterns and the expected absence of persistent high pressure, widespread MWH conditions are less likely than previously believed. NIWA’s SST update will continue to track this situation.

• January – March 2025 soil moisture levels and river flows are most likely to be near normal or below normal across the North Island and the east of the South Island, and near normal for the west and north of the South Island.

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