April 2013 was characterised by lower pressures than usual over New Zealand and to the south and west of the country, with higher pressures than normal to the east of the Chatham Islands. This meant more northwesterly winds than normal affected the country, resulting in a very warm month for many regions. Northwesterly fronts resulted in extremely heavy rainfall in the western Bay of Plenty on 20 April and in the Nelson and Tasman regions on 21 April.
New Zealand Climate Update 167 – May 2013
What happened in April, how our climate outlook for the previous three months turned out, global and local sea temperatures, and our outlook for May to July.
The equatorial Pacific Ocean remains in a neutral state (neither El Niño nor La Niña). International guidance indicates that these neutral conditions are likely to persist over the coming three months (May–July). In the New Zealand region higher pressures than normal are forecast south of the country extending towards the east of the Chathams Islands, while lower pressures than normal are expected to the north of New Zealand. This circulation pattern is expected to be associated with weaker than normal westerly flow.
Rainfall for the May – July period as a whole is likely to be in the near normal range for all regions.
Early winter (May–July) temperatures are very likely to be above average across the entire country. Nevertheless from time to time, cold snaps along with frosts in some areas are still expected as is typical of early winter.
Soil moisture levels and river flows are also likely to be in the near normal range for all regions.
For February-April 2013 (early autumn) slightly higher than normal pressures were expected to the south of the country and southeast of the Chatham Islands, with weak anomalous flows from the north-east quarter over New Zealand. Much higher pressures than expected however occurred over the New Zealand region for the period as whole extending well east of the country. This climate pattern brought enhanced easterly flows across northern areas of the country.