ENSO Wrap-Up
Current state of the Pacific and Indian oceans


Weekly sea surface temperatures

Graphs of the table values

Monthly sea surface temperatures

Graphs of the table values

5-day sub-surface temperatures

Monthly temperatures

Southern Oscillation Index

While the SOI is an important index that tracks changes in tropical air pressure, we consider a much wider range of atmospheric and oceanic conditions when we assess the status of ENSO. This includes winds, clouds, ocean currents and both surface and sub-surface ocean temperatures, as well as outlooks for the months ahead.

30-day SOI values for the past two years
Select to see full-size map of 30-day Southern Oscillation Index values for the past two years, updated daily.

Trade winds

5-day SST and wind anomaly from TAO/TRITON
Select to see full-size map of 5-day SST and wind anomaly from TAO/TRITON.

Cloudiness near the Date Line

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ENSO outlooks

NINO3.4 SST plumes from Bureau model forecasts, updated daily
Select to see full-size map of NINIO3.4 SST plumes from Bureau model forecasts, updated daily.

Indian Ocean Dipole outlooks

IOD SST plumes from Bureau model forecasts, updated daily
Select to see full-size map of IOD SST plumes from Bureau model forecasts, updated daily.

The SST map for September shows cooler than 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. Warmer than average SSTs were evident in the far western equatorial Pacific and in the Tasman Sea.

The September values of the three key NINO indices were: NINO3 −0.8 °C, NINO3.4 −0.7 °C, and NINO4 −0.3 °C.

The sea surface temperature (SST) map for the tropical Pacific Ocean for the week ending 11 October show cool anomalies extending across the tropical Pacific, covering areas east of 160°E and to the south of the equator in the eastern Pacific. Cool SST anomalies have again strengthened compared to last fortnight. Warm anomalies remain in the Maritime Continent and waters close to much of northern and eastern Australia.

The latest values of the three NINO indices in the tropical Pacific for the week ending 11 October were: NINO3 −0.9 °C, NINO3.4 −0.8 °C, NINO4 −0.5 °C.

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 30-day Southern Oscillation Index (SOI) for the 30 days ending 11 October was +11.7. The 90-day SOI value is also above La Niña thresholds at +9.3.

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 11 October were stronger than average over the western half of the tropical Pacific. More generally, Pacific trade winds have been stronger than average in recent months.

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 in the Maritime Continent, and is expected to increase in strength as it moves into the Western Pacific Ocean. At this time of the year, the MJO may increase the likelihood of above average rainfall over south-east Australia as it passes through the western Pacific.

Large parts of the central and eastern Indian Ocean are warmer than average. Compared to two weeks ago, warm sea surface temperature anomalies have strengthened in the west of the basin. The latest weekly value of the Indian Ocean Dipole (IOD) index to 11 October was +0.39 °C, a strong jump almost to positive IOD threshold values.

Three of the six surveyed climate models indicate values indicate the IOD will be met in November, however, a negative IOD event is now looking less likely compared to previous outlooks, following significant warming in the western pole. 

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 September) shows cooler than average water extending across the top 200 m of the sub-surface of the equatorial Pacific around and east of the Date Line.  The strength and extent of cooler than average water has increased month-on-month compared to both August and July.

Weak warm anomalies persist across large parts of the column depth in the western equatorial Pacific. 

For the five days ending 11 October, sub-surface temperatures were cooler than average in parts of the central to eastern equatorial Pacific, reaching more than 3 degrees cooler than average in a small region around 140°W between 100 and 150 m depth. These cool anomalies have weakened slightly compared to two weeks ago. Temperatures are close to average in most of the sub-surface of the equatorial Pacific Ocean. 

A La Niña is underway in the tropical Pacific. All surveyed international climate models indicate this La Niña will persist through the southern hemisphere summer 2020–21.

Most models suggest the La Niña will strengthen, peaking in December. Around half the models anticipate a strong event, meaning there is a possibility it could reach similar strength to the La Niña of 2010–12. However, models forecast this event will be shorter, possibly ending in the first quarter of 2021. The strength of La Niña impacts on Australia are often related to the strength of the event.

Central and eastern tropical Pacific Ocean sea surface temperatures remain around La Niña thresholds (0.8 °C below average) and atmospheric indicators, including the Southern Oscillation Index (SOI), trade winds and cloud, are also at La Niña levels.

La Niña typically increases the chance of above average rainfall across much of Australia during spring. Above average summer rainfall is also typical across eastern Australia. Current climate outlooks indicate November 2020 to January 2021 will be wetter than average for much of the country.

In the Indian Ocean, there has been significant warming of sea surface temperatures in the west of the Basin over the past fortnight. Models have reduced the likelihood of a negative IOD event in 2020, noting that the IOD typically breaks down in late spring or early summer.

The Southern Annular Mode (SAM) is expected to be positive for the remainder of October. La Niña tends to favour positive SAM during spring and summer, further enhancing the wet signal in the east.

The Madden–Julian Oscillation (MJO) is in the Maritime Continent and is expected to increase in strength as it moves into the Western Pacific Ocean.

Climate change is also influencing the Australian climate. Australia's climate has warmed by around 1.4 °C since 1910, while southern Australia has seen a 10–20% reduction in cool season (April–October) rainfall in recent decades.

The Southern Annual Mode (SAM) is expected to remain positive over the remainder of October. 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 of the international climate models surveyed by the Bureau indicate the current La Niña will persist until at least January 2021. Most models reach their peak in December, and all but one indicate thresholds will still be met in February.

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.

Product code: IDCKGEWW00