Weather forecasters are predicting that the strong El Nino conditions of spring 2015 will continue over summer and into autumn 2016. El Nino 2015-2016 could rank among the 4 strongest El Nino events recorded. Find out what farmers, growers and the rural community can do to be prepared.
Every El Nino is different and its impacts on New Zealand’s climate cannot be easily predicted. During El Nino, New Zealand generally experiences stronger or more frequent winds from the south-west in spring, and from the west in summer. This typically leads to:
El Nino will increase the chances of more frequent and extreme adverse weather events so farmers growers and the rural community need to think about how they will prepare.
El Nino is the extreme end of a natural cycle known as the El Nino Southern Oscillation, during which major changes in atmospheric and oceanic circulation result in a sustained period of warming in the central and eastern tropical Pacific.
El Nino occurs every 3 to 7 years on average, during which easterly Pacific trade winds weaken for a prolonged period or even reverse direction, moving warm surface waters eastward along the equator and preventing cold, deep water from upwelling on the tropical west coast of South America. This leads to extensive warming of large regions of the ocean and influences weather patterns across the Pacific.
Typically, El Nino peaks during the late Southern Hemisphere spring or early summer, and weakens in the following year. In moderate to strong El Ninos, sea surface temperatures are typically 2degC to 3degC above normal at their peak. Sea temperature anomalies at about 100m depth below the surface can be even larger. In 2015, there are reports of sub-surface temperatures reaching 5degC above normal in parts of the eastern tropical Pacific, which suggests the El Nino development is relatively strong.
In El Nino years, New Zealand tends to experience stronger or more frequent winds from the west in summer, leading to drought in east coast areas and more rain in the west. In winter, the winds tend to be more from the south, bringing colder conditions to both the land and the surrounding ocean. In spring and autumn, southwesterlies tend to be stronger or more frequent, providing a mix of the summer and winter effects.