During the summer of 2012-2013, anticyclones dominated the New Zealand area. Many places had little or no rainfall since early February.

The map below shows the average mean sea level pressure over the New Zealand area over Jan/Feb 2013. There's no doubt about the pressure being high and not changing very much. Because this map shows averaged pressures, we don't see the few troughs that passed across Aotearoa New Zealand during that time.

On Thursday 19 April 2012, New Zealand was completely surrounded by a very large High (or anticyclone). The air pressure at sea level was above 1030 hPa everywhere over New Zealand at midday on that day. Highest pressures were over inland Otago and Canterbury, peaking at 1039 hPa. Christchurch Airport was reporting 1038.2 hPa ... that's very high indeed.