September 19th, 2024
A northerly quarter air flow in mid-April could direct tropical moisture towards Aotearoa/New Zealand, increasing the likelihood of heavy rainfall, according to the National Institute of Water and Atmospheric Research (NIWA) Seasonal climate outlook April - June 2023 published on 31 March.
For the three-month period overall, rainfall is predicted to be near normal or above normal in the north and west of the South Island and near normal in all other regions. If the climate system shifts towards El Niño in the coming months, June could turn out drier than normal, particularly if southerly quarter winds prevail, according to NIWA.
La Niña concludes after three-year stint
After dominating the climate for three years, La Niña finally came to an end in March due to a significant change in tropical trade winds and warming seas across the equatorial Pacific. ENSO-neutral conditions have since emerged, but there is potential for El Niño conditions to arrive as early as winter, prompting the New Zealand government to issue an El Niño Watch.
↕️ April-June climate outlook: changeability is the theme!
— NIWA Weather (@NiwaWeather) March 31, 2023
A period of particularly active weather is possible in mid-April.
There's a real chance that El Niño conditions develop in winter, which could lead to drier & cooler weather than recent years...https://t.co/dZZQGHoWrU pic.twitter.com/JuUnYf5rx6
Mixed air flows expected during autumn
The transition between La Niña and El Niño is expected to bring increased variability to New Zealand's weather patterns. Autumn may see mixed air flows that could turn southerly around the start of winter, consistent with a developing El Niño. Consequently, the weather experienced in the previous month may not be a reliable indicator of the month ahead, according to NIWA which is a Crown Research Institute established in 1992.
Heavy rainfall potential in mid-April
A northerly quarter air flow in mid-April may direct tropical moisture towards Aotearoa/New Zealand, increasing the likelihood of heavy rainfall. For the three-month period overall, rainfall is predicted to be near normal or above normal in the north and west of the South Island and near normal in all other regions. If the climate system shifts towards El Niño in the coming months, June could turn out drier than normal, particularly if southerly quarter winds prevail.
Near normal rainfall in most regions
Various regions across New Zealand are predicted to experience near normal or above average temperatures and rainfall totals during April-June 2023. In the North Island, soil moisture levels and river flows are likely to be near normal or below normal. In contrast, near normal soil moisture levels are expected in the west of the North Island, while river flows may be near normal or below normal.
Warmer than average sea surface temperatures persist
Coastal sea surface temperatures (SSTs) in March ranged from 0.6˚C to 2.0˚C above average, with the eastern South Island experiencing the warmest SSTs on record since 1981. The persistence of these warmer than average SSTs makes a colder than average season unlikely, but more variable circulation and wind patterns will result in more variable temperatures. If El Niño develops, cooler winter temperatures could emerge, in contrast to recent record warm winters, increasing the risk of frosts.
Implications for agriculture and ecosystems
The changing weather patterns and potential arrival of El Niño could have significant implications for New Zealand's agriculture and ecosystems. Farmers may need to adapt their practices to accommodate the shifts in temperature, rainfall, and soil moisture levels, while also considering the possibility of more frequent frosts during winter. These factors may impact crop yields, water availability, and livestock health.
In addition, these changing conditions could affect New Zealand's native flora and fauna. Warmer sea surface temperatures may impact marine ecosystems, altering the distribution and abundance of fish species and potentially affecting the fishing industry. Furthermore, altered rainfall patterns could disrupt the breeding and migration habits of various bird species, as well as impact the growth and distribution of native plants.
Public preparedness and adaptation
As New Zealand faces these changing weather patterns and potential El Niño conditions, it is essential for the public to remain informed about the latest forecasts and potential impacts. Communities should be prepared for heavy rainfall events, which may increase the risk of flooding and landslides. Local authorities must also consider the long-term implications of these climatic shifts on infrastructure, such as roads and water management systems.
In light of the potential for more variable temperatures and the increased risk of frosts,NIWA advises that households should also prepare for the possibility of cooler winter conditions, ensuring that their homes are adequately insulated and heating systems are well-maintained.