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

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

Indian Ocean Dipole outlooks

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

For the week ending 19 November, sea surface temperatures (SSTs) were cooler than average along the equator in the central and eastern Pacific Ocean, extending southward along the coast of Peru in South America.

Compared to two weeks ago, cool anomalies now extend further into the central equatorial Pacific, but there has been a decrease in cool anomalies along the South American coast in the eastern Pacific south of the equator. Latest values for the week ending 19 November are: NINO3 −0.6 °C, NINO3.4 −0.5 °C, NINO4 −0.1 °C.

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 across waters around the southeast of Australia. In recent weeks warm anomalies in the western Pacific have resembled a horseshoe shape around the cool anomalies extending along the equator, which is a typical signature La Niña.

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.

The tropical Pacific is approaching La Niña thresholds. If the current progression continues, and thresholds are exceeded for a sustained period, 2017–18 will be considered a La Niña event. As a result, the Bureau’s ENSO Outlook has been raised to La Niña ALERT meaning there is approximately a 70% chance—or triple the normal likelihood—of La Niña occurring. Climate models suggest that any event is likely to be weak and short-lived. This means it is expected to be very different to the strong 2010–12 La Niña.

Oceanic indicators of ENSO show a clear progression towards La Niña. Tropical Pacific sea surface temperatures (SSTs) have cooled since late winter, and waters beneath the surface remain cooler than average in the eastern Pacific. However, they are currently just shy of La Niña thresholds. Atmospheric indicators such as the Southern Oscillation Index (SOI) and trade winds have shown signs of shifting into a La Niña-like state. In order for La Niña to become established, atmospheric and oceanic indicators need to be reinforcing each other ("coupled"), which will strengthen and sustain these changes (i.e. a positive feedback).

All international climate models suggest further cooling of the tropical Pacific is likely. All models reach La Niña thresholds in December 2017, and most maintain these values until at least February 2018.

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 La Niña, reducing the likelihood of widespread 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 typically 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 19 November 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 the next 1 to 3 months. All of the eight models anticipate that SSTs will reach or surpass La Niña thresholds by the end of 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. However, the models also suggest any La Niña may 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 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 19 November is +5.7 (90-day value +7.5). 30-day values have dropped back to the neutral side of La Niña threshold values during the past week. However, the 90-day value remains within the La Niña value range.

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 19 November was −0.20 °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 infulences.

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 19 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 140°W were more than 3 degrees cooler than average. Sub-surface water temperatures were generally average to slightly warmer than average in the western half of the equatorial Pacific.

Product code: IDCKGEWW00