New Zealand Climate Update 158 – August 2012

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

Current Climate - July 2012

July started unusually cold and dry, due to winter time anticyclones or ridges prevailing over the country during the first half of the month, bringing clear skies, light winds and a recipe for frost. Frosts during the period 1 July to 5 July were particularly severe. In stark contrast, northwest winds produced unusual warmth in eastern areas mid-month. During the last two weeks of July, lows dominated over the north Tasman Sea, bringing unusually mild conditions, northeast winds and high rainfall to northern and eastern regions of the North Island, as well as Nelson/Marlborough.

For the month as a whole, higher than normal pressures were observed over New Zealand and to the southeast, with lower pressures than usual over the north Tasman Sea. This resulted in more northeast winds than usual over the North Island. 

Global Setting – July 2012

Conditions in the tropical Pacific are currently on the brink of El Niño, and it is likely El Niño will develop during the early spring period. In the New Zealand region, however, lower pressures to the north of the country, and higher pressures to the south of New Zealand, are still likely to dominate for the August-October period. 

Outlook - August to October 2012

Sea temperatures around New Zealand are likely to be near normal for the August - October period as a whole. Early spring temperatures are likely to be near average or above average for all regions, which is in contrast to a typical El Niño early spring period. August-October rainfall is likely to be near normal or above normal in the north and east of the North Island, but below normal for the west, south and east of the South Island. For Nelson/Marlborough, and the southwest North Island, seasonal rainfall totals are likely to be in the near normal range. 

Retrospective - May to July Outlook

Neutral conditions were expected to prevail (neither La Niña nor El Niño), as was indeed the case. Near New Zealand, lower than normal pressures were predicted to the north of the country, with higher than normal pressures over southern New Zealand. This pressure pattern was well forecast; pressures over the north Tasman Sea were below seasonal normal, but pressures across the lower North Island, the entire South Island, and extending across to the Chatham Islands were much higher than usual.