New Zealand Climate Update 159 – September 2012

What happened in August, how our climate outlook for the previous three months turned out, global and local sea temperatures, and our outlook for September to November. 

Current Climate - August 2012

August 2012 was dominated by more northeast winds than normal over New Zealand, squeezed between higher than normal pressures southeast of the country, and lower pressures than usual over the mid Tasman Sea. The northeasterly winds also produced a very large contrast in rainfall across the Southern Alps. 

Global Setting – August 2012

Borderline El Niño conditions are present in the tropical Pacific, and a weak short-lived El Niño is predicted for the spring and summer periods. However, the seasonal forecast models do not yet show any sign of the enhanced southwesterly and westerly airflow over New Zealand that is usually associated with El Niño events. Over the spring period (September-November), higher than normal pressures are expected in the south Tasman and over southern New Zealand, along with lower pressures to the north of the North Island and weaker than normal westerlies over the country. 

Outlook - September to November 2012

Borderline El Niño conditions are present in the tropical Pacific, and a weak El Niño is likely over the spring and summer periods. However, enhanced southwesterly and westerly airflow over New Zealand that is usually associated with El Niño is not yet evident in the season forecast models. Thus, over the spring period (September-November), higher than normal pressures are expected in the south Tasman and over southern New Zealand, along with lower pressures to the north of the North Island and weaker than normal westerlies over the country. Sea temperatures around New Zealand are likely to be near normal for the season as a whole. 

Retrospective - June to August Outlook

Neutral conditions in the tropical Pacific were forecast to persist through much of winter, with a chance of El Niño developing by spring. This was an accurate prediction, in that threshold El Niño conditions now currently exist. Circulation patterns over New Zealand were forecast to be close to the seasonal norm, but this was not the case – a strong northeasterly anomaly affected New Zealand during winter, due to intense ridging (much higher than usual pressures) near the Chatham Islands.