February 2025 climate report

Key take away from this report

Northland region has received low rainfall for February, particularly the west coast. The southwest is very dry. Similar weather patterns can be expected in March.

Summary

• Northland region as a whole averaged 35.5% of the expected rainfall for February, with the west coast receiving < 10%.
• The SPI6 maps indicate that large areas of central and western Northland are “Severely Dry”.
• River flows are close to “Normal” in the northeast, “Low” in central and southern areas, and “Very Low” to “Extremely Low” in the west.
• Groundwater levels are generally “Normal” to “Above Normal” in the northeast, and “Low” to “Extremely Low” through the rest of the region.
• Soil moisture across the region is showing a sustained deficit with plants likely showing signs of distress/ lack of growth.
• Temperatures are very likely to be above average (45% chance) over the next three months.
• Rainfall totals are most likely to be near average (45% chance) over the next three months.
• River flows are likely to be below average (45% chance) or near normal (40% chance) over the next three months.
• Soil moisture levels are equally likely to be average (45% chance) to below average (45% chance) over the next three months.
• The weather for March is likely to be similar to February, with a small possibility of significant rainfall towards the end of the month.
• Conditions in Northland have steadily declined throughout February, the Kaipara district is particularly dry and experiencing moderate meteorological and hydrological drought, and low-level agricultural drought. The Far North and Whangārei Districts are dry but generally experiencing near normal dry conditions for this time of year.
• There is a risk that, if extended periods of low rainfall continue, parts of Northland, particularly in the southwest, could experience an increasing level of meteorological, hydrological, and agricultural drought (with lower river flows, groundwater levels, water reservoirs, and soil moisture etc.,) over the next three months.

Rainfall

February was very light on rainfall for all of Northland, with only an average 28.5 mm recorded (Figure 1), which was 35.5% of the expected average February Rainfall (Figure 2). The scattered rainfall that was recorded during the month was primarily around the Mangamuka and in the Eastern Ranges. The maximum recorded was 74 mm at Te Puhi at Mangakawakawa, followed by 69 mm at Whakapara. Close behind was Hakaru in the south of the region with 58.5 mm, and 55.5 mm at Kerikeri. The Minimum rainfall was recorded along the west coast, with Dargaville, Rotokakahi and Kai Iwi lakes all receiving less than 5 mm in February, while the Poutō Peninsula, Cape Reinga and Ruawai all received less than 10 mm. Compared to each site's average for February, Te Puhi at Mangakawakawa recorded 91% of expected, 69% in the Hikurangi Swamp, 66% at Hakaru and 61% in Whakapara. At the other end of the spectrum Dargaville, Rotokakahi, Kai Iwi Lakes and Waimamaku all received less than 10% of their expected rainfall for February.

Figures 1 and 2: February rainfall distribution for Northland in mm, and in percentage of median. Showing an average of 28.5 mm (35.5% of expected) rainfall for the region.

The standardised rainfall index (SPI) is useful to compare the rainfall in Northland as a whole, as the site-specific patterns are removed from the data. On a three-month scale between December – February (Figure 3) the SPI indicates “Near Normal” to ‘Moderately Dry’ conditions. On a six-month scale from September – February (Figure 4) however, the SPI indicates that large areas of Northland, particularly in central and western areas, are “Severely Dry”. The SPI helps understand the reserves in soil moisture, and river flow, and how quickly catchments will drain. The extended dry means that the region is likely to drain quicker than expected following rain events.

Figures 3 and 4: Standardised rainfall for Northland on a 3-month scale (November – February) and a 6-month scale (September – February).

River Flows

Northland’s river flows in February reflect the distribution of summer rainfall. Catchments in central and western areas of the region are “Low” - “Extremely Low”, with many of these rivers below Mean Annual Low Flow (MALF) at the start of March. Towards the north and east of the region catchments are recording “Normal” compared to the average flows for February.

Figure 5: River flows in Northland for February 2025.

Groundwater

Northland’s groundwater levels in February were “Normal” to “Above Normal” in the far north and east of the region, and “Low” to “Extremely Low” in central and western areas.

Figure 6: Groundwater levels in Northland’s primary monitored aquifers for February.

Soil moisture

Summary of modelled soil moisture data from NIWA

Soil Moisture steadily declined across the region through February (Figure 7). All sites are below 75 mm of deficit at the start of March. This is below the temporary wilting point for most plants, and there is likely to be little new/ continued growth. Dargaville and the rest of the west coast have spent all of February in a significant deficit, which reflects the low February rainfall, and plant distress is likely to be occurring (browning of pasture, slow or no plant growth, wilting etc). The soil moisture deficit is calculated based on incoming daily rainfall (mm), outgoing daily potential evapotranspiration (mm), and a fixed available water capacity (the amount of water in the soil 'reservoir' that plants can use) of 150 mm”.

Figure 7: Calculated daily soil moisture values at key areas around Northland, courtesy of NIWA, data ending 28th February 2025.

Climate Outlook for March – May 2025

Summary of climate forecasts from NIWA and MetService

After a dry February, Northland can expect the similar conditions to continue through March – May. La Niña conditions are weakening, and other climate drivers are currently in neutral states. Surface Sea temperatures around Northland are higher than usual and are expected to remain high through Autumn. Northland is likely to have “above average” temperatures, “average” rainfall, and “average – below average” river flows between March – May. (Table 1). March is likely to be dry, with a slight chance of rain systems developing at the end of the month, as high-pressure systems are predicted to break up at this time.

For more information visit the following links:

• Seasonal climate outlook March-May 2025 (NIWA)
• Get weather emails from MetService

Table 1: Forecasted likelihood of above, near or below average climate conditions for Northland from March – May 2025.

(Expressed as % likelihood).

NIWA Drought Index

The NIWA Drought Index (NZDI) on 1 March categorises the southwest of Northland as “Extremely Dry”, and the northwest of the region as “Dry” to “Very Dry”, (Figure 8). The index is based on the Standardised Precipitation Index, the Soil Moisture Deficit, the Soil Moisture Deficit Anomaly, and the Potential Evapotranspiration Deficit, with a value less than 0.75 considered normal – wet. At a District level, The Far North and Whangārei Districts are on average “near normal” which is a marked improvement compared to January, while the Kaipara District ranges between “Very Dry” and “Extremely Dry” (Figure 9).

Figure 8: NIWA New Zealand Drought Index produced 3 March 2025.

Figure 9: NIWA drought index tracking for the Far North, Whangārei and Kaipara districts from 2018 - 2025.

NIWA35 Forecasting Tool

NIWA’s drought prediction tool combines rainfall, soil moisture, and evapotranspiration to estimate the risk of meteorological drought, over the next 35 days.

The forecast from 1/3/2025 to 4/4/2025 predicts a low risk of “very dry” (90th percentile) conditions for majority of Northland, and possible drought development in the southwest of the region (Figure 10). In all scenarios, the southwest of Northland is likely to be dry.

The rainfall prediction for the region for the same period is that Northland will most likely be dry to very dry (50th percentile), receiving 50 – 80% of the expected rainfall for March, with some areas receiving less than 50% (Figure 11).

The NIWA35 forecasting tool can be rerun every week, and is most reliable for the two weeks following the forecast. : NIWA35 forecasting tool at shiny.niwa.co.nz

Figure 10: Drought risk assessment for Northland from NIWA35 from 1 March 2025.

Figure 11: Rainfall prediction for Northland from NIWA35 from 1 March. There is a moderate risk of dry to very dry conditions (50th percentile).

Northland Drought Risk Assessment

The drought risk assessment (Table 2) provides a visual summary of the current conditions of Northland’s rainfall, river flows, and groundwater levels and the current state of water resources. It also incorporates NIWA’s Climate Outlook and Drought Index, and MetService Forecasts.

The Northland region received 35.5% of the expected rainfall for February, with the west coast receiving less than 10% of the expected Rainfall.

River flows are generally “Normal” to “Above Normal” in the northeast “Low” in central and southern areas, and “Very Low” to “Extremely Low” in the west. There has not been a sustained recovery in river catchments due to prolonged low rainfall and soil moisture levels during spring and summer. Some river flows, primarily in western catchments, are now below the residual minimum flow requirements for various consented water takes, including some district water supplies.

Groundwater levels are generally “Normal” to “Above Normal” in the northeast, and “Low” to “Extremely Low” through the rest of the region.

Soil moisture levels are below average across the region, except in Kerikeri which is average. All areas are below the temporary wilting point. The West coast is particularly low with a sustained two-month long soil water deficit.

NIWA’s climate outlook for the next three months predicts that rainfall will most likely be average, and river flows and soil moisture are most likely to be average to below average. Little rainfall is expected until the end of March when there is a low probability of a rainfall event coming to fruition.

Conditions in Northland have steadily declined throughout February, the Kaipara district is particularly dry and experiencing moderate meteorological and hydrological drought, and low-level agricultural drought. The Far North and Whangārei Districts are dry but generally experiencing near normal dry conditions for this time of year.

There is a risk that, if extended periods of low rainfall continue, parts of Northland, particularly in the southwest, could experience an increasing level of meteorological, hydrological, and agricultural drought (with lower river flows, groundwater levels, water reservoirs, and soil moisture etc.,) over the next three months

Table 2: Drought Risk assessment matrix.

Tropical Cyclone Outlook

Summary of NIWA and MetService Outlooks

Late summer through early autumn is considered to be the peak of the tropical cyclone season.

On average at least one ex-tropical cyclone (TC) passes within 550km of New Zealand (NZ) each year (Figure 12). This season the risk is considered normal to elevated until April.

If an ex-TC tracks close to NZ, there is a near equal probability of it tracking to the east or west of the North Island. An ex-TC entering the NZ region could produce significant rainfall, severe winds, hazardous marine conditions and coastal damage.

Figure 12: Number of predicted named tropical cyclones interacting with an island group for the 2024-25 season.