Seasonal Climate 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 0.8˚C to 1.6˚C 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.

Regional predictions for January – March 2025

The tables below show the probabilities (or percent chances) for each of three categories: above average, near average, and below average. In the absence of any forecast guidance there would be an equal likelihood (33% chance) of the outcome for any of the three categories. Forecast information from local and global guidance models is used to indicate the deviation from equal chance that is expected for the coming three-month period. All outlooks are for the three months as a whole. There will inevitably be relatively wet and dry days, and hot and cold days, within a season. The exact range in temperature and rainfall within each of the three categories varies with location and season. However, as a guide, the “near average” or middle category for the temperature predictions includes deviations up to ±0.5°C relative to the long-term mean, whereas for rainfall the “near normal” category lies between 80 per cent and 120 per cent of the long-term (1991-2020) mean.

Northland, Auckland, Waikato, Bay of Plenty

• Temperatures are likely to be above average (50% chance).   
• Rainfall totals are about equally likely to be near normal (35% chance) or above normal (40% chance).  Unusually dry conditions are expected through about the middle part of January.  However, occasional heavy rainfall events cannot be ruled out as the season progresses.
• Soil moisture levels and river flows are both about equally likely to be near normal (35% chance) or below normal (40% chance).

	Temperature	Rainfall	Soil moisture	River flows
Above average	50	40	25	25
Near average	40	35	35	35
Below average	10	25	40	40

Central North Island, Taranaki, Whanganui, Manawatu, Wellington

Probabilities are assigned in three categories: above average, near average, and below average.

• Temperatures are likely to be above average (50% chance).   
• Rainfall totals are about equally likely to be near normal (35% chance) or above normal (40% chance).  Occasional heavy rainfall events cannot be ruled out as the season progresses.
• Soil moisture levels and river flows are both about equally likely to be near normal (35% chance) or below normal (40% chance).

	Temperature	Rainfall	Soil moisture	River flows
Above average	50	40	25	25
Near average	40	35	35	35
Below average	10	25	40	40

Gisborne, Hawke’s Bay, Wairarapa

Probabilities are assigned in three categories: above average, near average, and below average.

• Temperatures are likely to be above average (50% chance).   
• Rainfall totals are about equally likely to be near normal (35% chance) or above normal (40% chance).  Occasional heavy rainfall events cannot be ruled out as the season progresses.
• Soil moisture levels and river flows are both about equally likely to be near normal (35% chance) or below normal (40% chance).

	Temperature	Rainfall	Soil moisture	River flows
Above average	50	40	25	25
Near average	40	35	35	35
Below average	10	25	40	40

Tasman, Nelson, Marlborough, Buller

Probabilities are assigned in three categories: above average, near average, and below average.

• Temperatures are about equally likely to be near average (45% chance) or above average (40% chance).
• Rainfall totals are about equally likely to be near normal (40% chance) or above normal (35% chance).  Occasional heavy rainfall events cannot be ruled out.
• Soil moisture levels and river flows are both likely to be near normal (40% chance).

	Temperature	Rainfall	Soil moisture	River flows
Above average	40	35	30	30
Near average	45	40	40	40
Below average	15	25	30	30

West Coast, Southern Alps and foothills, inland Otago, Southland

Probabilities are assigned in three categories: above average, near average, and below average.

• Temperatures are about equally likely to be near average (45% chance) or above average (40% chance).
• Rainfall totals are most likely to be near normal (45% chance).  After a period of unusually dry weather through about mid-January, the pattern is expected to favour increased periods of unsettled conditions.
• Soil moisture levels and river flows are equally likely to be near normal (40% chance) or below normal (40% chance).

	Temperature	Rainfall	Soil moisture	River flows
Above average	40	30	30	30
Near average	45	45	40	40
Below average	15	25	30	30

Coastal Canterbury and the nearby plains, east Otago

Probabilities are assigned in three categories: above average, near average, and below average.

• Temperatures are about equally likely to be near average (45% chance) or above average (40% chance).
• Rainfall totals are most likely to be near normal (45% chance). 
• Soil moisture levels and river flows are about equally likely to be near normal (40% chance) or below normal (35-40% chance).

The full probability breakdown is:

	Temperature	Rainfall	Soil moisture	River flows
Above average	40	25	20	25
Near average	45	45	40	40
Below average	15	30	40	35

Graphical representation of the regional probabilities

Background

Sea surface temperatures (SSTs) were leaning toward La Niña in the central equatorial Pacific (Niño 3.4 index) during December (-0.66°C).  The area of cooler-than-average ocean temperatures along the equatorial Pacific expanded westward and reached just west of the International Date Line.  The relative Niño 3.4 Index (RONI) was -1.19°C for the past 30 days (to 1 January 2025), reflective of the central equatorial Pacific being significantly cooler than the average of the global tropics and being in La Niña territory.

The Southern Oscillation Index (SOI) is technically in La Niña range (+1.83 at of 31 December 2024)  However large intra-seasonal variability has characterized the SOI during December, with recent daily values being slightly negative (i.e. on El Niño side of neutral).

During December, upper oceanic heat content was above average to the west of 160°E, with values exceeding +1.5°C confined to the westernmost parts of the Maritime Continent.  Meanwhile, significant negative anomalies (exceeding -2.0°C ) intensified around about 150°W.

In addition, the sub-surface equatorial Pacific remained 3°C to 5°C cooler than average between 50m and 100m depth east of the International Date Line.  The West Pacific Warm Pool has contracted westward and warmer than average sub-surface temperatures have intensified in the eastern Indian Ocean, exceeding +5°C anomalies at about 90°E.

In summary, sub-surface and surface temperature anomalies along the Equator remained in place in December 2024.  Several oceanic and atmospheric indicators have ventured into La Niña territory at times during the month, but overall, the ocean and the atmosphere have failed to fully and consistently couple.  Thus, conditions still fall short of a full-fledged La Niña event.

There still is large uncertainty as to whether official La Niña thresholds will be met over the coming season: guidance from international forecast models that NIWA monitors indicates decreasing chances for La Niña (about 40%) and an increasing probability for ENSO-neutral conditions (about 60%) over the outlook period.

Regardless of whether or not La Niña is officially declared over the forecast period, the risk for weather patterns that are broadly consistent with La Niña  remains.  However, as noted above, the somewhat unusual characteristics with the location of sea surface temperature anomalies in the central equatorial Pacific, and warmer than average sea surface temperatures in the far eastern tropical Pacific, increases the likelihood for more atypical air flows and weather patterns than are commonly associated with La Niña.

A “La Niña Watch” remains in effect. NIWA will continue to actively monitor oceanic and atmospheric patterns across the Pacific, and we encourage the public and especially climate sensitive sectors to keep up to date with our Seasonal Climate Outlooks throughout the summer, and to make use of the New Zealand drought dashboard, which provides 35-day outlooks of rainfall and drought, updated once daily: https://niwa.co.nz/weather-forecasting/seasonal-climate-outlook.

The Southern Annular Mode (SAM) was mostly negative during the month of December (74% of days negative in December) and remained in the neutral range overall.  Recently however, the SAM has increased and has been positive since 24 December 2024 and is forecast to gradually decrease to negative values as we progress towards mid-January.

The Indian Ocean Dipole (IOD) index remained negative during most of December but remained in the neutral range, with the average anomaly for the month of December being -0.51°C.  The guidance from the Australian BoM is for the IOD to remain neutral throughout the forecast period.

During December, convective forcing associated with the MJO reached the Maritime Continent (phase 5).  The forecast is for convective activity associated with the MJO to move through the Maritime Continent through the first two weeks of January, then weaken from mid-month as it passes through the Western Pacific (phases 6 and 7) and toward the western hemisphere (phases 8 and 1) by the end of January.

Sea surface temperatures (SSTs) around New Zealand remained generally above average in December, with anomalies ranging from about +0.9°C to +1.6°C  by the end of the month, but marine heatwave conditions (MHW) 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 MHW conditions 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 will continue to monitor the situation in the SST update.

Forecast Confidence

Temperature

Rainfall