March 2013 was dominated by anticyclones ('highs') which were slow moving over and to the east of New Zealand. These highs generally kept rain-bearing weather systems such as lows and fronts away, resulting in a dry, sunny, and warm March for many regions. The remains of ex-tropical cyclone Sandra and an active cold front interrupted this pattern, causing very heavy rainfall on the 18th in the lower North Island.
New Zealand Climate Update 166 – April 2013
What happened in March, how our climate outlook for the previous three months turned out, global and local sea temperatures, and our outlook for April to June.
The equatorial Pacific Ocean remains in a neutral state (neither El Niño nor La Niña). International guidance indicates that neutral conditions are very likely to continue over the next three months (April–June). In the New Zealand region higher pressures are likely to prevail over and to the south of the South Island during the season.
In the New Zealand region higher pressures are likely to prevail over and to the south of the South Island during the period April to June. Temperatures from April to June are likely to be above average across the country. Rainfall for the April – June period as a whole is likely to be in the near normal range. For this tropical cyclone season (November – April), the risk of an ex-Tropical Cyclone approaching New Zealand is expected to be near normal. On average, one ex-Tropical Cyclone nears New Zealand during the season.
Neutral conditions in the tropical Pacific (neither El Niño nor La Niña) were forecast to persist through January-February-March 2013. This outlook was correctly forecast with the Southern Oscillation Index (SOI), trade winds, and tropical cloud patterns all continuing at neutral levels.
Lower than normal pressures were expected in the south Tasman and to the southeast of the Chatham Islands, with enhanced south-westerly winds over New Zealand during the January-February-March period. Much higher pressures than expected however occurred over the New Zealand region extending well east of the country.