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 3 December, sea surface temperatures (SSTs) were cooler than average along the equator in the central and eastern Pacific Ocean, extending southward across much of the South Pacific close to South America.

Compared to two weeks ago, SSTs in the central equatorial Pacific have cooled and expanded in area across the eastern South Pacific. Latest values for the week ending 3 December are: NINO3 −0.9 °C, NINO3.4 −0.8 °C, NINO4 −0.2 °C.

Weak warm anomalies persist across much of the far western Pacific, extending well into the north and south of the basin. Warm anomalies across the tropical western Pacific and extending away from the tropics in the north and south continue to resemble the horseshoe shape typical of La Niña.

Very warm SST anomalies were evident across the Tasman Sea, extending from waters to the west of Tasmania to the east of New Zealand; these shallow warm anomalies were aided by a long-lived blocking high pressure system and associated light winds and sunny skies. 

Persistent NINO3 or 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.

The Bureau’s ENSO Outlook has been raised to LA NIÑA, indicating that the tropical Pacific has reached La Niña levels. Climate models suggest this La Niña will be weak and short-lived, persisting until early southern autumn 2018.

Signs of La Niña in the equatorial Pacific have increased during spring. The central to eastern tropical Pacific Ocean has cooled steadily since winter, and is now at La Niña thresholds (0.8 °C below average). Atmospheric indicators, including the Southern Oscillation Index (SOI), trade winds and cloud, also show clear La Niña patterns.

In order for 2017–18 to be classed as a La Niña year, the event needs to last for at least 3 months. Climate models surveyed by the Bureau suggest that while this event is likely to persist over the southern summer, it will be weaker than the strong La Niña of 2010–12.

La Niña typically brings above average rainfall to eastern Australia during late spring and summer. However, sea surface temperature patterns in the Indian Ocean and closer to Australia are not typical of a La Niña event, reducing the likelihood of widespread above average summer rainfall. La Niña can also increase the chance of prolonged warm spells for southeast Australia.

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

Cloudiness near the Date Line remains below average (positive OLR anomalies). 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 3 December were stronger than average across the western half of the tropical Pacific, and near average in the east.

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 over summer. All of the eight models reach or surpass La Niña thresholds during December 2017. Seven of the eight models sustain the conditions long enough to be considered an event, where persistence for three months is generally the minimum length required.

Model outlooks generally suggest any La Niña will be short lived, with tropical Pacific sea surface temperatures warming again by late summer. 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 November show SSTs were cooler than average in the eastern to central 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 surrounding southeastern Australia and the South Island of New Zealand.

The November value for NINO3 was −0.7 °C, NINO3.4 −0.6 °C, and NINO4 −0.1 °C. All three NINO indices were cooler than October values.

The 30-day Southern Oscillation Index (SOI) to 3 December is +11.1 (90-day value +8.9). 30-day values have been above La Niña threshold values for the past week and a half, after a two week dip back just into neutral values. The 90-day value remained within the La Niña value range during this dip.

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 3 December was +0.05 °C. All six 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.

However, to the south of the traditional Indian Ocean Dipole regions, cooler than average sea surface temperatures in the eastern Indian Ocean may be limiting the feed of moisture over Australia, and opposing more typical La Niña influences.

The four-month sequence of sub-surface temperature anomalies (to November) 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 3 degrees cooler than average for November. In general terms, the extent and strength of sub-surface temperature anomalies have declined slightly compared to those for October. Weak warm anomalies persist in the top 150 m of the far western equatorial Pacific.

The sub-surface temperature map for the 5 days ending 4 December 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 up to 100 m depth east of around 120°W were more than 2 degrees cooler than average. Sub-surface water temperatures were slightly warmer than average across much of the sub-surface of the western half of the equatorial Pacific. While weak, this is a pattern typical of La Niña.

Product code: IDCKGEWW00