New Zealand Climate Update 160 – October 2012

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

Current Climate - September 2012

Spring westerlies arrived during the first few days of September, and prevailed during the first half of the month.  These stormy westerly quarter winds produced very wet conditions on the West Coast of the South Island, but in contrast, a rather dry month in eastern areas of both islands.  From mid-month, a pattern change saw more anticyclones than usual lie over New Zealand and to the east of the country.  This combination of patterns resulted in more northwest winds than normal over New Zealand for the month of September, overall.

Global Setting – September 2012

The Pacific Ocean is still close to El Niño thresholds, but the atmosphere has yet to show patterns typical of El Niño. The global forecast models indicate the conditions are likely to remain close to thresholds or transition towards a weak and short-lived El Niño over the next three months. For New Zealand however they do not show signs of the southwesterly and westerly anomalies that are usually associated with El Niño events. Higher than normal pressures are expected South of Australia and New Zealand at the mid-latitudes, and lower pressures than normal are forecast to the north of the North Island. This pattern is expected to be associated with weaker than normal westerly flow over the country. 

Outlook - October to December 2012

The Pacific Ocean is still close to El Nino thresholds, but the atmosphere has yet to show patterns typical of El Nino. The conditions are likely to remain close to thresholds or transition towards a weak and short-lived El Nino over the next three months. No signs of the enhanced southwesterly and westerly airflow over New Zealand that is usually associated with El Niño events however are forecast for the October – December season. Higher than normal pressures are expected South of Australia and New Zealand at the mid-latitudes, and lower pressures than normal are forecast to the north of the North Island. 

Retrospective - July to September Outlook

Over the early spring period, neutral conditions (neither La Niña nor El Niño) were expected to give way to the development of an El Niño.  To reflect this, circulation in the New Zealand region was forecast to transition from northeasterly to westerly flow anomalies by the end of the season, as El Niño conditions settled in.  This was a correct forecast, as threshold El Niño conditions were present by September, and although the seasonal (July-September) circulation anomaly over New Zealand was northeasterly, September was notable for more westerly to northwesterly flows than usual.