Monday 28 November 2022

La Niña declines, return to neutral conditions likely in early southern autumn

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MELBOURNE, Australia — La Niña continues its decline, with sea surface temperatures in the central tropical Pacific Ocean warming over the past fortnight, reports the Bureau of Meteorology of the Australian Government.

Most models indicate a return to neutral conditions is likely early in the southern autumn.

The decline of this La Niña is evident in oceanic and atmospheric patterns, with several indicators recently returning to levels more consistent with a neutral ENSO phase.

Sea surface temperatures are very close to neutral levels, cloudiness near the Date Line has increased, and trade winds are generally near normal across the equatorial Pacific.

However, the current pulse of the Madden-Julian Oscillation (MJO) has been strong, and the effects of wind variations associated with it is likely to have amplified the decline.

As the MJO progresses east, its effect will reverse, meaning some La Niña indicators are likely to strengthen briefly.

Four of eight international climate models surveyed by the Bureau maintain La Niña values through March. By May, only one model still exceeds La Niña thresholds. For July, all eight are within the neutral range.

This ENSO event has had relatively little effect on Australian rainfall patterns over the 2017–18 summer.

The Indian Ocean Dipole (IOD) is currently neutral. IOD events are unable to form between December and April.

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