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 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.

Sea surface temperatures (SSTs) are warmer than average along the equator in the Pacific Ocean, and across much of the tropics to the north of the equator. Compared to two weeks ago, SSTs have warmed across the western half of the tropical Pacific. SSTs within the NINO3 region have now touched upon the El Niño threshold value.

The latest values of the key NINO indices in the tropical Pacific for the week ending 21 October are: NINO3 +0.8 °C, NINO3.4 +0.7 °C and NINO4 +0.9 °C, reflecting the concentration of anomalous warmth in the western Pacific.

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.

Around Australia, SSTs are mostly close to average for this time of year, although a small area near the coast of southeast Australia has warmed significantly over the past two weeks and is currently much warmer than average.

The Bureau's ENSO Outlook remains at El Niño ALERT, indicating there is approximately a 70% chance of El Niño occurring in 2018—around triple the normal likelihood. In the Indian Ocean there are signs that a positive Indian Ocean Dipole (IOD) is underway.

An El Niño and a positive IOD increase the likelihood of a dry and warm end to the year across most of Australia. They also raise the risk of heatwaves and bushfire weather in the south, while there are typically fewer tropical cyclones in the Australian region.

The surface of the tropical Pacific has warmed over the past month due to weakening of the trade winds. Sub-surface waters also remain warmer than average, increasing the potential for further warming at the surface. However, atmospheric indicators in the tropical Pacific such as the Southern Oscillation Index (SOI), cloudiness and trade winds, are yet to indicate that the ocean and atmosphere have coupled and hence are reinforcing each other. A positive feedback between the ocean and atmosphere is what defines and sustains an El Niño event.

International climate models suggest further warming of the tropical Pacific Ocean is likely, increasing the chance of coupling occurring in the coming months. Six of eight models predict El Niño thresholds will be met or exceeded in November.

The IOD index has exceeded the positive threshold (+0.4 °C) for five of the last six weeks. If these values persist for anther fortnight, 2018 will be considered a positive IOD year. Model outlooks suggest the positive IOD event will decay during November. The IOD is linked with drier weather in southern and central Australia during spring, but typically has little influence on Australian climate from December to April.

 

Cloudiness near the Date Line has generally remained below average (positive OLR anomalies) since mid-September. While decreased cloudiness near the Date Line is typically a signal seen during La Niña, the broader pattern across the tropical Pacific is consistent with neutral ENSO. Again, this indicates that coupling of the ocean and atmosphere has yet to occur.

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

Trade winds for the five days ending 21 October were near average across the tropical Pacific. This again suggests that the atmosphere and ocean have yet to start reinforcing each other, which is required for an event to become firmly established.

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.

All but one of the surveyed international climate models predict further warming of central equatorial Pacific sea surface temperatures (SSTs) over the coming months.

Six of the eight models surveyed indicate El Niño thresholds are likely to be met or exceeded during November 2018, with a seventh reaching threshold values later during the summer. El Niño onset during November or December would be later than usual, although not unprecedented.

 

Sea surface temperature (SST) for September were slightly warmer than average across the equatorial Pacific Ocean, but within the neutral ENSO range. The South Pacific and large parts of the central and eastern North Pacific were warmer than average.

The September values for NINO3 were +0.3 °C, NINO3.4 +0.3 °C, and NINO4 +0.6 °C.

The 30-day Southern Oscillation Index (SOI) to 21 October was −2.1, and the 90-day SOI was −3.9. The SOI has remained within the neutral ENSO range for the past two weeks. The lack of a clear signal in the SOI indicates that the atmospheric circulation required to signal the start of an El Niño event, and to reinforce and sustain an El Niño, is not yet present.

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.

A positive Indian Ocean Dipole (IOD) is likely underway. The latest weekly index value to 21 October was +0.45 °C. These values need to persist until at least November for 2018 to be considered a positive IOD year.

The passage of tropical cyclone Luban across the Arabian Sea and north of the Indian Ocean appears to have temporarily cooled sea surface temperatures near the western node of the IOD, but warm SST anomalies generally persist across most of the northern Indian Ocean. Waters near the Indonesian island of Sumatra (close to the eastern node of the IOD) and near northwestern Australia are close to average.

All of the six international climate models surveyed by the Bureau indicate that the positive IOD event will breakdown during November; this would be in line with the typical seasonal pattern of the IOD. Due to the movement of the monsoon trough in the Indian Ocean, the IOD typically has little influence on Australian climate from December to April. When the monsoon trough shifts southwards into the southern hemisphere, it changes the broadscale wind patterns, meaning that the IOD pattern is unable to form. 

A positive IOD event typically reduces spring rainfall in central and southern Australia, and can exacerbate any potential El Niño driven rainfall deficiencies.

The four-month sequence of sub-surface temperature anomalies (to 18 October) shows warm anomalies in the sub-surface have increased significantly compared to the preceding months. A large pool of warmer than average water extends across the sub-surface of the equatorial Pacific, between about 160°E to about 100°W. Parts of this region are more than 3 degrees warmer than average.

Temperatures for the five days ending 21 October show warmer than average waters in the top 200 m of the sub-surface of the equatorial Pacific. A large volume of the sub-surface is more than 3 degrees warmer than average, and extends from around 150 m depth in the central equatorial Pacific to around 50 m depth at the eastern edge of the equatorial Pacific.

Warm anomalies have continued to progress eastward over the past two weeks. The eastward shift of anomalously warm water is a typical precursor of El Niño.

Product code: IDCKGEWW00