January 2013 was a month of two halves – and two Islands. During the first half of the month, more northwesterly winds than usual affected the South Island, bringing unsettled weather and several heavy rainfall events to the South Island. But high pressures prevailed over the North Island during this time – meaning any fronts actually making it across the North Island "fizzled" – producing very little rainfall. The second half of January was characterised by an intense 'blocking high' which became slow moving over, and to the east of, the country. This produced extremely sunny and dry conditions for New Zealand over the second half of the month. The net result overall was an extremely dry January for the North Island, but a relatively wet month for the South Island.
New Zealand Climate Update 164 – February 2013
What happened in January, how our climate outlook for the previous three months turned out, global and local sea temperatures, and our outlook for February to April.
The ocean – atmosphere system in the tropical Pacific is currently in a neutral state (neither El Niño nor La Niña) and the global forecast models indicate that these conditions are highly likely to persist into the autumn. In the New Zealand region, slightly higher than normal pressures are expected to the south of the country and southeast of the Chatham Islands, with weak anomalous flow from the north-easterly quarter over New Zealand.
Conditions in the tropical Pacific are neutral (neither El Nino nor La Nina). While the equatorial SSTs in the eastern Pacific are currently slightly cooler than normal, they fall within the neutral range and all atmospheric indicators are close to their climatological values. The global forecast models indicate a very high likelihood (~ 95 %) of ENSO-Neutral conditions to persist into the autumn 2013. In the New Zealand region, slightly higher than normal pressures are expected south of the country as well as southeast of the Chatham Islands, with weak anomalous flow from the north-easterly quarter over the country. February-April temperatures are likely to be average in all regions but for the north of the North Island, where average or above average temperatures are expected. Sea surface temperatures are expected to be near average around New Zealand. Rainfall is likely to be near normal for all regions but for the North of the North Island, where normal or above normal rainfall is forecast. 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.
Over the November-January (early summer) period, weakly enhanced southwest winds were (correctly) predicted over New Zealand. Higher pressures than usual were observed over the season over the Tasman Sea, with lower than normal pressures to the southeast of the Chatham Islands.