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

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.

For the week ending 6 November, sea surface temperatures (SSTs) were cooler than average along the equator in the central and eastern Pacific Ocean, extending southward in a broad band along the coast of much of South America.

Compared to two weeks ago, there has been cooling in some areas of the tropical Pacific, notably south of the equator in the east, and along the equator in the central Pacific. Latest values for the week ending 5 November are: NINO3 −0.5 °C, NINO3.4 −0.4 °C, NINO4 +0.2 °C. However, the NINO4 index, covering the central to western equatorial Pacific, has warmed by 0.3 °C compared to two weeks ago.

Weak warm anomalies persist across much of the far western Pacific, extending well into the north and south of the basin. Stronger warm anomalies continue to the south of Japan, and along large parts of the east coast of Australia.

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

While the El Niño–Southern Oscillation (ENSO) remains neutral, the Bureau’s ENSO Outlook is currently at La Niña WATCH. La Niña WATCH means there is approximately a 50% chance of La Niña forming in late 2017. Climate models note that if La Niña does occur, it is likely to be short lived and weak, and effects upon Australian climate less than during the last La Niña in 2010–12.

Tropical Pacific sea surface temperatures (SSTs) have cooled since late winter. However, recent cooling has stalled slightly due to a pulse of tropical activity (known as the Madden-Julian Oscillation). Cooling is expected to resume in the coming fortnight. Atmospheric indicators of ENSO, such as the Southern Oscillation Index (SOI) and cloudiness near the Date Line have shown signs of shifting into a La Niña-like state.

All international climate models suggest further cooling of the tropical Pacific is likely, with most models reaching La Niña thresholds in late 2017. Six of eight models suggest that these levels will persist long enough to be considered an event. If La Niña does develop, it is likely to be weak and short-lived.

La Niña events typically bring above average rainfall to eastern Australia during late spring and summer. However, current temperature patterns in the Indian Ocean would typically push Australia's climate into a drier phase. Hence current climate outlooks do not favour typical La Niña rainfall patterns across Australia for November to January. Weak La Niña events can also increase the chance of prolonged heatwaves for southeast Australia.

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

Cloudiness near the Date Line has been below average (positive OLR anomalies) during the past two weeks. Cloudiness values have been generally below average since early August.

Equatorial cloudiness near the Date Line typically increases during El Niño (below average OLR) and decreases during La Niña (above average OLR).

Trade winds for the 5 days ending 5 November were generally near average strength across the tropical Pacific.

The strong Madden-Julian Oscillation event that occurred two weeks ago has now finished. The MJO is currently weak or indiscernible. This means it is no longer influencing the trade winds.

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

International climate models surveyed by the Bureau indicate that further cooling of equatorial Pacific Ocean sea surface temperatures is expected during spring and summer. All of the eight models anticipate that SSTs will reach or surpass La Niña thresholds by January, with most reaching the threshold during November.

However, the models also suggest any La Niña may be short lived, with tropical Pacific sea surface temperatures warming again by late summer. Persistence for three months is generally considered the minimum length required to be considered an event; six of the eight the models sustain the event for a sufficient period. Warming back towards neutral levels in late summer is typical of the ENSO cycle at that time of year.

Sea surface temperature (SST) anomalies for October show SSTs were cooler than average in the eastern equatorial Pacific Ocean and along the coast of Peru in South America. Generally weak warm anomalies were present across most of the South Pacific, the western Pacific, and the mid-latitudes of the North Pacific. Areas of stronger warm anomalies in excess of one degree above average were observed along parts of the east coast of Australia, although having decreased in areal extent compared to September. Similar anomalies were observed in an area south of Japan, and in the mid- to high latitudes to the east of New Zealand.

The October value for NINO3 was −0.4 °C, NINO3.4 −0.3 °C, and NINO4 +0.1 °C. All three NINO indices held steady compared to September values.

The 30-day Southern Oscillation Index (SOI) to 6 November is +7.4 (90-day value +7.4), remaining just within the La Niña value range. 30-day SOI values have been above La Niña thresholds since the start of October.

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

The Indian Ocean Dipole (IOD) is neutral. The weekly index value to 5 November was +0.14 °C. All of the climate models surveyed by the Bureau indicate that the IOD will remain neutral into early 2018.

The influence of the IOD on Australian climate is weak during December to April. This is because the monsoon trough shifts south over the tropical Indian Ocean changing wind patterns, which prevents the IOD pattern from being able to form.

The four-month sequence of sub-surface temperature anomalies (to October) shows cool anomalies persist across most of the equatorial Pacific Ocean down to a depth of 200 m. In a small area of the central equatorial Pacific sub-surface anomalies are more than 4 degrees cooler than average for October. In general terms, the extent and strength of sub-surface temperature anomalies has declined slightly compared to those for September, and very weak warm anomalies have emerged in the far western equatorial Pacific.

The sub-surface temperature map for the 5 days ending 5 November shows a pool of slightly cooler than average water in the subsurface of the eastern half of the equatorial Pacific Ocean. Water temperatures in an area around 100 m depth at around 150°W to 130°W were more than 3 degrees cooler than average. Sub-surface water temperatures were generally close to average across full column depth of the western half of the equatorial Pacific.

Product code: IDCKGEWW00