Climate Driver Update history
Climate drivers in the Pacific, Indian and Southern oceans and the Tropics

Persistent NINO3 or NINO3.4 values warmer than +0.8 °C are typical of El Niño, while persistent values cooler than −0.8 °C typically indicate La Niña.

The El Niño–Southern Oscillation (ENSO) and Indian Ocean Dipole (IOD) remain neutral. While neutral ENSO is likely for the southern hemisphere winter, some model outlooks suggest a La Niña-like state will develop in the tropical Pacific Ocean during spring. Most models suggest a negative IOD will develop in the Indian Ocean from mid-winter, but model skill is low at this time of year.

The IOD is currently neutral. Most international climate models surveyed by the Bureau suggest the development of a negative IOD from the middle of the southern hemisphere winter. However, each of the models show a broad spread of likely scenarios between the neutral IOD and negative IOD range, and more recent model outlooks having slightly lower likelihoods of negative IOD. Accuracy of IOD forecasts is low for forecasts made during autumn, with accuracy improving in winter. A negative IOD typically brings above average winter–spring rainfall to southern Australia.

Key indicators of ENSO, such as the Southern Oscillation Index (SOI), trade winds, cloudiness near the Date Line and sea surface temperatures in the tropical Pacific Ocean, generally persist at neutral ENSO levels. However, sea surface temperatures across the tropical Pacific Ocean have cooled over the past several weeks. This has been supported by recent cooling of tropical Pacific sub-surface temperatures.

International climate models surveyed by the Bureau indicate that ENSO is likely to stay neutral through the southern hemisphere winter. However, by early-to-mid spring, three models of the eight models currently reach or exceed La Niña levels. Like model outlooks for the IOD, ENSO predictions made during autumn tend to have lower accuracy than predictions made at other times of the year. This is because development of both ENSO and the IOD have greater sensitivity to random weather factors at this time.

The Bureau's ENSO Outlook is currently at INACTIVE. However, if recent cooling at both the surface and beneath the surface of the tropical Pacific Ocean persists, and any more models suggest La Niña-like conditions in spring, the ENSO Outlook will shift to La Niña WATCH.

The Southern Annular Mode (SAM) is currently positive and forecast to remain positive for the coming two weeks. However, it isn't expected to have a significant effect on rainfall during this time due to interactions with other climate drivers and local weather conditions.

Cloudiness near the Date Line has generally been below average since early to mid-March. Overall cloud patterns are consistent with neutral ENSO.

Equatorial cloudiness near the Date Line typically increases during El Niño (negative OLR anomalies) and decreases during La Niña (positive OLR anomalies).

Trade winds for the 5 days ending 24 May were close to average across most of the tropical Pacific, consistent with neutral ENSO conditions.

During El Niño there is a sustained weakening, or even reversal, of the trade winds across much of the tropical Pacific. Conversely, during La Niña, there is a sustained strengthening of the trade winds.

While most of the eight international climate models surveyed by the Bureau indicate central tropical Pacific sea surface temperatures in the NINO3.4 region will remain at ENSO-neutral levels through the southern hemisphere winter, two models exceed the La Niña threshold during September, and another model approaches the threshold in October.

ENSO predictions made during autumn tend to have lower accuracy than predictions made at other times of the year. This means that ENSO forecasts made during autumn should be used with some caution, with accuracy increasing for ENSO forecasts made during winter.

ENSO events — El Niño or La Niña — typically begin to develop during autumn, before strengthening in winter/spring. The Bureau will continue to closely monitor the potential for either to develop this year.

Monthly SSTs for April were slightly warmer than average across most of the equatorial Pacific Ocean, extending more broadly across much of the western half of the basin south of the equator, with surface waters also warmer than average around much of Australia.

The April values of the three key NINO indices were: NINO3 +0.5 °C, NINO3.4 +0.5 °C, and NINO4 +0.5 °C.

The 30-day Southern Oscillation Index (SOI) for the 30 days ending 24 May was +1.8. The 90-day value was −2.3. Both values are well within the ENSO neutral range.

Sustained negative values of the SOI below −7 typically indicate El Niño while sustained positive values above +7 typically indicate La Niña. Values between +7 and −7 generally indicate neutral conditions.

The Indian Ocean Dipole (IOD) is currently neutral. The latest weekly value to 24 May is +0.31 °C.

Model outlooks indicate the IOD is likely to become negative over the coming months.

Of the six international climate models that the bureau surveys, four models reach negative IOD levels at some point in July or August and remain above the threshold during September and October. However, at this time of year the accuracy of IOD forecasts beyond autumn is low.

A negative IOD typically brings above average winter–spring rainfall to much of southern Australia.

The four-month sequence of equatorial sub-surface temperature anomalies (to 21 May) shows cooler than average waters extend in a band across most of the equatorial Pacific, between about 100 and 200 m in the western to central equatorial Pacific and rising to a depth of around 50 m at the eastern edge of the equatorial Pacific.

In the western equatorial Pacific very weak warm anomalies persist in the top 150 m, but have decreased in strength and extent compared to April.

Since January, warm anomalies in the western equatorial Pacific near the surface have decreased, while the pattern of cooler anomalies at depth has strengthened.

For the five days ending 24 May, sub-surface temperatures were cooler than average across much of the equatorial Pacific between 50 and 200 m depth. The volume of cooler than average water has decreased slightly compared to two weeks ago, with a large volume of water in the central to eastern equatorial Pacific sub-surface remaining more than 3 degrees cooler than average.

Elsewhere in the sub-surface of the equatorial Pacific Ocean, sub-surface temperatures were generally close to average.