With the University of Montana, Virginia Tech and Texas A&M University Wintermester programs starting in under two weeks, students will be pleased to hear that a moderate to strong La Niña is well-established in the South Pacific.

La Niña and the opposite El Niño, refer to extremes of the Southern Oscillation (ENSO) cycle, when major changes in the Pacific atmospheric and oceanic circulation occur. The changes all lie in the differing strength of the trade winds. During normal conditions, trade winds blow westward across the Pacific, piling up warm surface water so that Indonesian sea levels are approximately 50 cm higher than those in Ecuador and cool, nutrient–rich sea water “wells up” off the South American coast. Relatively cold sea temperatures extend along the equator from South America towards the central Pacific. High rainfall occurs in the rising air over the warmest water to the west, whereas the colder east Pacific is relatively dry.

During El Niño events the trade winds weaken, leading to a rise in sea surface temperature in the eastern equatorial Pacific and a reduction of “up–welling” off South America. Heavy rainfall and flooding occur over Peru, and drought over Indonesia and Australia occurs. The supplies of nutrient rich water off the South American coast are cut off due to the reduced up–welling. Adversely during La Niña events, the trade winds strengthen, and the pattern is a more intense version of the normal conditions, with an even colder sea surface temperature in the eastern equatorial Pacific.

They are both characterised in New Zealand by variable levels of winds and rainfall in different parts of New Zealand. So with a La Niña temperatures are likely or very likely to be above average for this time of year (November to January) across the whole country and rainfall is likely to be normal or below normal over the South Island of New Zealand – check out the National Institute of Water and Atmospheric research (NIWA) website for more info!

So hopefully those Wintermester students are in store for some fantastic weather for their programs – all the better for the kayaking on the Abel Tasman (above), climbing the Fox Glacier (right) and all the other awesome activities on the New Zealand Program!