La Nina conditions have been officially declared by scientists at BoM but it may not be long lasting or impact NZ the way you might think, says WeatherWatch.co.nz.

For months La Nina has been on the cards with the pervious outlook by BoM (Bureau of Meteorology) saying there was a 70% chance of La Nina forming this summer. Despite Tuesday’s (Nov 23) confirmation La Nina has officially formed, international modelling still points to it not being long lasting – perhaps similar to La Nina we had last summer, which despite the big rain forecasts by other outlets many regions saw droughts actually expand.

La Nina is measured at the equatorial Pacific and New Zealand is located about halfway between the equator and Antarctica…this means the weather conditions (the rain events and big lows) that La Nina tends to produce north of us may still miss New Zealand as they try to track southwards.

But typically the warmer than average sea surface temperatures produced in a La Nina summer leads to more cloud in northern and eastern New Zealand (both islands), an increased chance of inland severe thunderstorms, higher humidity for many regions (making for milder nights) and a better chance of getting rain (but sometimes only drizzle which doesn’t accumulate to much) for the north and north east of both main islands.

NZ also typically gets more easterlies in the upper North Island (which we’ve certainly had past month or two) and more nor’easters in eastern areas further down the country, right down to Coastal Otago (and this can make it cooler by day in places like Dunedin, Christchurch and Napier – again something many have noticed lately).

But the Southern Ocean weather patterns remain active and busy/spring-like, which means this somewhat borderline La Nina may not dominate NZ’s weather the same way it’s dominating Australia already with very wet weather along their eastern seaboard.

La Nina is currently forecast through December and January and most likely February too. Neutral conditions (closer to normal sea surface temperatures) are likely by March (at this stage).

WeatherWatch.co.nz says NZ can often have long dry stretches with La Nina but there’s an increased number of drizzly/wetter days and also a heightened chance of an ex-tropical cyclone (or subtropical low) impacting NZ too (which can bring localised flooding, as we recently saw in Gisborne).

CLIMATEWATCH!

Our final ClimateWatch outlook for the year will be issued next week (Video and News Story/Maps). We’ll take a look at the rainfall chances this December and the 3 month Summer outlook for temperatures and expected rainfall thanks to our exclusive access to the IBM supercomputer, Watson. We’ll have more details then about how La Nina may impact your weather in the weeks/months ahead.

*BoM is the most trusted Government Climate Forecaster in the South West Pacific and are a true public agency.