February 2013 was characterised by anticyclones ('highs') which were slow moving over New Zealand. These highs, or anticyclones, kept rain-bearing weather systems such as lows and fronts away, resulting in an extremely dry and sunny February for many regions of the country.
New Zealand Climate Update 165 – March 2013
What happened in February, how our climate outlook for the previous three months turned out, global and local sea temperatures, and our outlook for March to May.
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 (March-May). Lower pressures than usual are likely over the north Tasman Sea during autumn, with slightly higher pressures than usual over and to the south of New Zealand.
Atmospheric indicators of ENSO, such as the Southern Oscillation Index (SOI), trade winds, and tropical cloud patterns continue at neutral levels. International guidance indicates that the tropical Pacific Ocean is very likely to remain neutral over the next three months (March-May). Lower pressures than usual are likely over northern Australia, with high pressures south of New Zealand. Autumn temperatures are likely to be above average across the South Island, and average to above average in the North Island. Rainfall for the March – May 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 (neither El Niño nor La Niña) were (correctly) projected for the summer period. In the New Zealand region, lower than normal pressures were expected southeast of the Chatham Islands, with enhanced south-westerly winds over New Zealand. Whilst observed pressures were lower than usual southeast of the Chatham Islands, and more southwesterly winds than usual were experienced over the country, the stand-out feature of summer was the unusual prevalence of anticyclones (highs) over both the Tasman Sea and also well to the east of the North Island.