Seasonal Climate Outlook November - January 2025

Outlook summary:

• A La Niña Watch remains in effect, with a little over 50% chance that La Niña officially develops by the end of the year. However, this event is likely to be weak and short-lived and might stay below traditional La Niña thresholds.  
• There are indications for more widespread dry conditions than what is typical for La Niña across much of New Zealand, especially at the beginning of the three-month outlook period, rainfall is most likely to be near normal in the east of the North Island, and about equally likely to be near normal or below normal for all remaining regions of the country.
• Chances for more anticyclonic conditions over and to the southeast of New Zealand may lead to dry spells developing, especially in the west of both islands. La Niña-like conditions could on the other hand bring short and intense rain events for the north of the North Island and the eastern parts of both islands. Monitor NIWA35 for updates.
• Air temperatures are very likely to be above average across the country. An increased prevalence of northeasterly winds may lead to more days above 25˚C than normal during November-January.

• Coastal sea surface temperatures (SSTs) ranged from 0.55˚C to 1.01˚C above average during October. Marine heatwave conditions were occurring near the southeast of the North Island and east of the South Island, and to a lesser extent along the west coast of the North Island. Monitor the SST update for updates, which suggests marine heatwave conditions may intensify in the months ahead.
• November-January soil moisture levels and river flows are most likely to be near normal in the east of the South Island. In the west of the North Island, near normal soil moisture levels are most likely, and river flows are equally likely to be near normal or below normal. For all other regions of the country, soil moisture levels and river flows are about equally likely to be near normal or below normal.
• Soil moisture levels at depth continue to be below normal in the east of the North Island while soil moisture is normal in the east of the South Island.

Regional predictions for November 2024 – January 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 for 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 very likely to be above average (65% chance).
• Rainfall totals are about equally likely to be near normal (40% chance) or below normal (35% chance). While the prevalence of high pressure over New Zealand could lead to extended dry periods, La Niña-like conditions could bring infrequent short and sharp rain events from the north for the region.

• 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	65	25	20	20
Near average	30	40	40	40
Below average	05	35	40	40

Central North Island, Taranaki, Whanganui, Manawatu, Wellington

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

• Temperatures are very likely to be above average (60% chance).

• Rainfall totals are about equally likely to be near normal (40% chance) or below normal (35% chance). More northeasterly winds associated with developing La Niña-like conditions may contribute to extended dry spells in the region.
• Soil moisture levels are most likely to be near normal (45% chance) 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	60	25	20	20
Near average	35	40	45	40
Below average	05	35	35	40

Gisborne, Hawke’s Bay, Wairarapa

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

• Temperatures are very likely to be above average (60% chance).
• Rainfall totals are most likely to be near normal (45% chance) for November-January as a whole, but short-term guidance indicates that drier than normal conditions are likely for much of November. Later on, La Niña-like conditions could bring infrequent short and sharp rain events for the region.

• Soil moisture levels and river flows are about equally likely to be below normal (45% chance) or near normal (40% chance).

	Temperature	Rainfall	Soil moisture	River flows
Above average	60	20	15	15
Near average	35	45	40	40
Below average	05	35	45	45

Tasman, Nelson, Marlborough, Buller

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

• Temperatures are very likely to be above average (65% chance).
• Rainfall totals are about equally likely to be near normal (40% chance) or below normal (35% chance). Consistent with potential La Niña-like conditions, more northeasterly winds may cause dry spells, especially for the western part of the region.
• Soil moisture levels and river flows are about equally likely to be near normal (40% chance) or below normal (35% chance).

	Temperature	Rainfall	Soil moisture	River flows
Above average	65	25	25	25
Near average	30	40	40	40
Below average	05	35	35	35

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

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

• Temperatures are very likely to be above average (60% chance). More northeasterly winds may contribute to more days above 25˚C than normal.
• Rainfall totals are about equally likely to be below normal (40% chance) or near normal (35% chance). Consistent with La Niña-like conditions, northeasterly quarter flow anomalies may cause extended dry spells during the three-month period.

• 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	60	25	20	20
Near average	35	35	40	40
Below average	05	40	40	40

Coastal Canterbury and the nearby plains, east Otago

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

• Temperatures are very likely to be above average (65% chance). Northeasterly quarter wind anomalies could lead to warmer nights but cooler days.
• Rainfall totals are about equally likely to be near normal (40% chance) or below normal (35% chance). While the prevalence of high pressure over New Zealand could lead to extended dry periods, bouts of northeasterly winds could bring infrequent short and sharp rain events for the region.
• Soil moisture levels and river flows are most likely to be near normal (45% chance).

The full probability breakdown is:

	Temperature	Rainfall	Soil moisture	River flows
Above average	65	25	25	25
Near average	30	40	45	45
Below average	05	35	30	30

Graphical representation of the regional probabilities

Background

Sea surface temperatures(SSTs) remained in the neutral range in the central equatorial Pacific (Niño 3.4 Index) during October (-0.34˚C), decreasing from -0.25˚C at the end of September. As of 29 October, the 30-day relative Niño 3.4 Index^* (RONI) was -1.05˚C, reflective of the central equatorial Pacific being significantly cooler than the average of the global tropics.

The Southern Oscillation Index (SOI) was on the La Niña side of neutral during October (+0.6) and August-October (+0.5) but trending towards La Niña-like conditions compared to September.

During October, upper-oceanic heat content was about 1.0˚C to 1.5˚C below average in the eastern and central equatorial Pacific (centred around 125˚W), halting the cooling trend observed in September, particularly in the central part of the basin. This signals a La Niña pattern failing to fully materialise yet in the upper ocean. ENSO neutral conditions are favoured to continue through November. A progression in a La Niña-like direction is still expected, however chances for La Niña to develop by January are now sitting at 53%, a decrease in the percentage chance compared to last month (60%), reflecting an increase in

forecast uncertainty for what would now become an unseasonably late La Niña development. NIWA will continue to actively monitor oceanic and atmospheric patterns across the Pacific and a “La Niña Watch” remains in effect. Sea surface temperatures in the tropics remain much higher than normal, which may influence the atmospheric response and weather patterns associated with La Niña to potentially develop. No two La Niña events are alike, a concept that may be more pertinent in a world that features widespread above average sea temperatures.

The Southern Annular Mode (SAM) was mostly negative during October (73% of days negative), with the latest (28 October) 30-day average anomaly being ­0.57. The forecast, however, is for the SAM index to return to positive values in early November, and then hover around mostly neutral values through the month.

The Indian Ocean Dipole (IOD) index became negative in October, and the latest (to 29 October) 30-day anomaly is ­0.51. While a negative IOD is typically associated with developing La Niña events and the eastern Indian Ocean is accordingly warmer than average, the western Indian Ocean remains close to or moderately warmer than average and negative IOD values are not forecast to be sustained beyond November.

During October, convective forcing associated with the Madden-Julian Oscillation (MJO) transitioned from the western Indian Ocean (phase 1) to the Maritime Continent (phase 5) as was forecast last month. During the first week of November, the convectively active phase of the MJO is forecast to further propagate eastward (phases 6 and 7) albeit with weaker amplitude. While phases 6 and 7 have historically been associated with wet conditions in the north and east of the North Island and drier than normal conditions in the southwest of the South Island, short-term (sub-seasonal) guidance favours mostly widespread dry conditions over the next three weeks.

Climate-sensitive sectors are encouraged 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.

New Zealand’s coastal water temperatures remained higher than average in October. Marine heatwave conditions are occurring near the southeast of the North Island and east of the South Island, and to a lesser extent along the west coast of the North Island. Model guidance suggests that increasing SSTs are likely in the New Zealand region through the next three months, with the potential for intensifying marine heatwave conditions. For more info, see the NIWA Sea Surface Temperature Update.

Forecast confidence

Temperature

Rainfall