April 2025 climate report

Key take away from this report

What a difference a month makes, heavy rainfall across the region has lifted drought conditions and all soils around the region at field capacity.

Summary

• Drought conditions have ended with the region receiving an average of 400% of the expected rainfall for April.
• All key catchments are recording above average flows.
• Groundwater levels are varied for key aquifers across the region with majority currently recording “low” water levels.
• Between May – July, temperatures and rainfall are expected to be “above average” while flows and soil moisture levels are expected to be “near average".

Rainfall

The Northland region has gone from one extreme to the other during April, after multiple months of region wide deficits, April was significantly wetter than average with three weather events moving across the region. Most of the rainfall fell in the north and east of the region. On average Northland recorded 403 mm of rain, which is 400% of the average rainfall for April. The highest rainfalls were at Wiroa Road (Kerikeri) with 721 mm, followed by Touwai (east of Kaeo) with 686 mm.

The lowest rainfall was on the west coast, Poutō Point recorded 121.6 mm, and Kai Iwi Lakes received 187.5mm. Percentage wise the Waitangi catchment received between 613% and 577% of the April average, while the lowest area was Kai Iwi Lakes with 199% of the expected rainfall for April.

Figures 1 and 2: April rainfall distribution for Northland in mm, and in percentage of median. Showing an average of 20 mm (22% 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. Looking back three months (February – April) the region is Near normal, with the east and northern areas of the region wetter than average. Over a six-month period (November – April) the pattern is slightly drier. Around the Whangārei area on both a three- and six-month period the area is moderately dry, which is a result of the drought conditions throughout summer and early autumn.

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

River Flows

River flows in all catchments in Northland are “Above Average” following a month of heavy rainfall.

Figure 5: River flows in Northland for April 2025.

Groundwater

Groundwater levels in Northlands key monitored aquifers in April range from “Extremely Low” to “Above Normal”. This regional variation is primarily due to differences in aquifer geology, as recharge occurs at different rates in reaction to the rainfall recorded across the region.

Figure 6: Groundwater levels in Northland’s primary monitored aquifers for April 2025.

Soil moisture

Soil Moisture has recovered across the region, Cyclone Tam in the first week of April moved Kaitaia and Kerikeri to field capacity, the rest of the rainfall in the month has resulted in run off in the area. Other sites in the region required both weather warnings are reached field capacity later in the month. Moving into May and the winter months, areas are likely to remain at similar levels. Flooding is likely to occur quickly with further rain events as there is little capacity in the soil. 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, ending in April 2025.

Note: Some graphs above do not have all March and April data available, due to a sensor malfunction and no data collected.

Climate Outlook for May – July 2025

Summary of climate forecasts from NIWA and MetService

The ENSO, as the main climate driver for New Zealand is in the neutral range and these conditions are expected to remain between May and July. However, La Nina like weather events expected to continue as the region settles. Majority of the expected weather for Northland is expected to be from the northeast, with low pressure systems still forming in the islands, there is a higher risk for heavy rainfall events to continue heading into winter. In Northland Temperatures and rainfall are likely to be “above average” while soil moisture and river flows are likely to be “near average”.

For more information visit the following links:

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

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

(Expressed as % likelihood).