Is La Niña in our future or not?

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And... what would that mean for New Zealand?

This animation shows current sea surface temperature anomalies in the Pacific. It shows how far they are from normal for this time of the year.

[Image Source: EarthWindMap. Data Source: National Centers for Environmental Prediction]

The "blue/purple tongue" running along the equator represents cooler than usual water and is one piece of the La Niña puzzle.

To officially get a La Niña, the cooler than usual water needs to:

1. be located across the central and eastern equatorial Pacific
2. be at least 0.7°C cooler than it normally is for 3 consecutive months
3. be forecast to persist for several more months.

A reflection that the ocean and atmosphere are coupled, or working together, also helps a forecaster's confidence that a La Niña event might be unfolding. This involves looking at weather phenomena such as trade winds, the Southern Oscillation Index, and rainfall patterns near the equator.

Currently, while the ocean is leaning very slightly in the direction of a La Niña, there has been little La Niña reflection in the atmosphere. As such, there is only about a 50% chance that La Niña conditions will officially develop in the next few months.

If not, neutral conditions should hold on across the equatorial Pacific. Neutral is the state or status that most commonly exists. That is, a status of the ocean and atmosphere that is neither reflective of La Niña or El Niño.

The National Oceanic and Atmospheric Administration (United States) recently cancelled their La Niña watch based on this very slow development.

Even if La Niña was to not "officially" develop, this cooler than usual pocket of water at the equator could have some influence on weather patterns around New Zealand.

It may promote more northeasterly winds than usual and higher pressures than normal over the South Island and to the south of the country. As a result, folks in the north and east of the North Island may experience wetter, warmer, and more humid conditions than normal while those to the west of the Alps could have drier conditions than are typically experienced.

Contacts and more information

For more on long term climate, check out our Seasonal Climate Outlook or contact:

Ben Noll
NIWA forecaster
Ph 09 375 6334.

Research subject: Wind