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 nearly the entire 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 entire equatorial Pacific. Despite this shift in pattern and continued warming, SSTs within the NINO regions remain within the range consistent with neutral ENSO. However, they are now close to El Niño thresholds.

The latest values of the key NINO indices in the tropical Pacific for the week ending 7 October are: NINO3 +0.7 °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, with areas near the southeast and northwest coast slightly warmer than average.

The Bureau's ENSO Outlook has been raised to El Niño ALERT. This means there is approximately a 70% chance of El Niño occurring in 2018—around triple the normal likelihood. Similarly, in the Indian Ocean, a positive Indian Ocean Dipole (IOD) may have started.

When combined, these two events in spring increase the possibility of a dry and warm end to the year. It also raises the risk of heatwaves and bushfire weather in the south, but reduces the risk of tropical cyclone activity in the north.

The tropical Pacific Ocean has warmed in recent weeks due to weakening of the trade winds, while the Southern Oscillation Index has fallen to typical El Niño levels. Models suggest further warming of the Pacific is likely. Four of eight models predict El Niño thresholds will likely be exceeded in the coming months, with another two falling just short.

In the Indian Ocean, there are signs that a positive IOD is currently underway. The IOD index has exceeded the threshold (+0.4 °C) for the last four weeks. However, these values must persist until November for it to be considered a positive IOD event. Model outlooks suggest positive IOD values are likely to continue through the austral spring, before returning to neutral values in late November to December.

Cloudiness near the Date Line has fluctuated around average values since mid-August, but has generally remained on the positive side since mid-September.

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 7 October were weaker than average across most of the tropical Pacific, with reversed (westerly) winds observed over the far west of the equatorial Pacific. The Madden-Julian Oscillation (MJO) is likely contributing to the current weakening of trade winds in the western Pacific.

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

Four of the eight surveyed models indicate El Niño thresholds will be exceeded for December 2018, with two others falling just short of the threshold.

El Niño onset during 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 7 October was −7.7, and the 90-day SOI was −4.5. The 30-day SOI value has exceeded the El Niño threshold value (−7) for two weeks.

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.

The Indian Ocean Dipole (IOD) has been displaying signs of a positive IOD event for a number of weeks. The weekly index value to 7 October was +0.58 °C. The IOD index has now remained above the positive IOD threshold value (+0.4 ºC) for four weeks. Along with warm SST anomalies across most of the northern Indian Ocean and cool anomalies near the Indonesian island of Sumatra, this strongly suggests that a positive IOD event is currently underway; nevertheless, these values need to persist until at least November for this to be considered an event.

Four of the six international climate models surveyed by the Bureau suggest that index values will remain above positive IOD thresholds for the remainder of October. All models expect a return to neutral by December. The IOD typically has little influence on Australian climate from December to April.

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 September) shows a persistent pool of slightly warmer than average water in the equatorial Pacific. During September the small pool of slightly cooler than average water in the shallow sub-surface of the eastern equatorial Pacific, which had emerged in August, decreased in both strength and volume. Warm anomalies extend to depth in the central to western equatorial Pacific, and remain generally similar compared to earlier months.

Temperatures for the five days ending 7 October show water was warmer than average across the sub-surface of the equatorial Pacific between 100 m and 200 m depth in the central Pacific, and rising into the top 100 m depth in the east. The strongest anomalous warmth was observed in the central Pacific, with a small area of the sub-surface more than 4 degrees warmer than average.

Warm anomalies have strengthened and continues to progress eastward over the past two weeks. While the overall state of the sub-surface remains consistent with neutral ENSO, sub-surface warming and the eastward shift of anomalously warm water may indicate imminent development of El Niño.

Product code: IDCKGEWW00