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

The SST map for October shows below average SSTs extending along the equator in the central and eastern tropical Pacific Ocean, and into the tropics south of the equator in the east of the basin. The extent of these cool anomalies has increased in central parts of the basin, as well as along the Chilean coast. Warmer than average SSTs were evident in the far western equatorial Pacific and in the Tasman Sea.

The October values of the three key NINO indices were: NINO3 −0.8 °C, NINO3.4 −1.0 °C, and NINO4 −0.5 °C.

The 30-day Southern Oscillation Index (SOI) for the 30 days ending 22 November was +5.7. The SOI has returned to values more consistent with La Niña. The earlier dip in 30-day SOI values followed the passage of the Madden-Julian Oscillation (MJO) through the Maritime Continent earlier in the 30-day period. The 90-day SOI value was +7.9.

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.

Trade winds for the 5 days ending 22 November were stronger than average over the western half of the tropical Pacific. Trade winds have increased in strength compared to two weeks ago.

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.

The Madden–Julian Oscillation (MJO) is over the eastern Indian Ocean. It is expected to become weak or indiscernible as it moves from the Indian Ocean into the Maritime Continent. The MJO is expected to move into the Australian region during early December; this could lead to an increase in moisture over northern Australia and favourable conditions for monsoon onset at Darwin.

Large parts of the Indian Ocean are warmer than average, but the Indian Ocean Dipole (IOD) is neutral. The latest weekly value of the IOD index to 22 November was −0.2 °C.

Compared to two weeks ago, there has been significant cooling across the far west of the Indian Ocean and to the south of the basin, with cool anomalies in some areas around and south of 30°S.

All but one of the six surveyed climate models expect the IOD to remain neutral through summer.

Cloudiness near the Date Line was below average over the past fortnight and has generally been below average since early to mid-March.

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

The four-month sequence of equatorial Pacific sub-surface temperature anomalies (to 19 November) shows cooler than average water extending across the top 200 m of the sub-surface of the equatorial Pacific from around the Date Line and eastward across the basin.  The strength and extent of cooler than average water has increased month-on-month since July.

Weak warm anomalies persist across large parts of the column depth in the far western equatorial Pacific. Compared to October, these warm anomalies now extend further eastward at depth, covering the area around the Date Line below 150 m depth.

For the five days ending 22 November, sub-surface temperatures were below average in the eastern equatorial Pacific, reaching more than 3 degrees below average in a region between 140°W and 110°W at 50 to 150 m depth. These cool anomalies cover a larger region than they did two weeks ago. In the west, weak warm anomalies, reaching more than 2 degrees above average, extend between about 100 to 150 m depth west of 170°W.

La Niña continues in the tropical Pacific. International climate models suggest it is likely to continue to at least February 2021.

Central and eastern tropical Pacific Ocean sea surface temperatures (SSTs) are at La Niña levels. Models suggest the current La Niña will strengthen further, peaking in December 2020 or January 2021 at moderate to strong levels.

Most oceanic and atmospheric indicators reflect a mature La Niña. Recent variability in the Southern Oscillation Index have been related to the Madden–Julian Oscillation (MJO), rather than the state of the La Niña.

The Southern Annular Mode (SAM) is neutral but is expected to increase to positive values over the coming week. This is driven in part by the La Niña influence, and in part by a stronger than average polar vortex over Antarctica. Positive values are expected at least into early 2021, and typically increase rainfall in south eastern Australia.

The Madden–Julian Oscillation (MJO) is at weak to moderate strength, having moved from the Atlantic to the eastern Indian Ocean in November. This pattern tends to be unfavorable for rain in Australia. The MJO is expected to weaken as it moves over Indonesian longitudes, though may bring increased rainfall over parts of northern Australia and be favourable for monsoon onset when it moves past the Top End.

Climate change is also influencing the Australian climate. Rainfall across northern Australia during its wet season (October–April) has increased since the late 1990's, with a greater proportion of high intensity short duration rainfall events.

Climate outlooks indicate December 2020 to February 2021 rainfall is likely to be above average for most of the country. Current La Niña conditions, though not as strong as 2010–12, warmer than average waters to the north of Australia, climate change and a positive SAM are contributing to the increased chances of rainfall over Australia. The state of the Indian Ocean is not as conducive to increased rainfall as it was during 2010–12.

The Southern Annual Mode (SAM) is currently neutral, but is expected to be generally positive into at least early 2021. La Niña tends to favour positive SAM during the spring to summer months, which typically enhances the La Niña wet signal in eastern Australia.

All international climate models surveyed by the Bureau indicate the current La Niña will likely persist until at least February 2021. Most climate models reach their peak in December, with some peaking in January. Six of eight models indicate thresholds will still be met in March, although all six show central Pacific sea surface temperatures much declined from their summer peak.

While some models indicate that the current La Niña could possibly reach similar strength to the La Niña of 2010–12, La Niña conditions are currently weaker than at the same point in 2010. Sea surface temperatures in the central and eastern tropical Pacific are the coolest since the end of the La Niña event in 2012, but they are not as cool as during spring or early summer 2010.

La Niña increases the likelihood of above average rainfall across much of Australia during spring, and across much of eastern Australia during summer. La Niña increases the chance of cooler than average daytime temperatures for large areas. It also increases the chance of tropical cyclones, and earlier first rains of the northern wet season.