Climate Driver Update history
Climate drivers in the Pacific, Indian and Southern oceans and the Tropics

Sea surface temperatures (SSTs) for the week ending 8 December remain warmer than average across most of the equatorial Pacific Ocean, particularly in the far west, though have cooled slightly compared to two weeks ago. Overall, patterns are consistent with a neutral ENSO state.

Compared to two weeks ago, SSTs around Australia have warmed, particularly to the west and northwest of Australia. SSTs are up to 2 degrees warmer than average across much of the eastern Indian Ocean, while a very small area of cool anomalies persist on the southern side of the Indonesian archipelago. This warming of the eastern Indian Ocean has resulted in continued weakening of the positive IOD. In the west of the Indian Ocean, warm SSTs anomalies have decreased slightly, but remain 1 to 2 degrees warmer than average.

Waters to the south of Australia and across Bass Strait were cooler than average.

The latest values of the three key NINO indices in the tropical Pacific for the week ending 8 December were: NINO3 +0.4 °C, NINO3.4 +0.4 °C and NINO4 +0.8 °C.

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.

The El Niño–Southern Oscillation (ENSO) remains neutral, and the positive Indian Ocean Dipole (IOD) event continues but has weakened.

IOD values have gradually weakened since their peak of +2.1 °C in mid-October. However, the latest weekly value of +0.9 °C is still well above the positive IOD threshold value of +0.4 °C. Warmer than average waters persist near the Horn of Africa, but the cooler than average waters in the eastern Indian Ocean have now returned to near-average sea surface temperatures. Trade winds remain stronger than average over the tropical Indian Ocean. Most international climate models surveyed by the Bureau indicate the positive IOD will dissipate by mid-summer as the monsoon moves into the southern hemisphere.

Typically, a positive IOD brings below average rainfall to southern and central Australia with warmer days for the southern two-thirds of the country. Positive IOD events are often associated with a more severe fire season for southeast Australia. Recent flooding in eastern Africa is also typical of a positive IOD event.

In the tropical Pacific Ocean, the El Niño–Southern Oscillation (ENSO) remains neutral. However abnormally warm sea surface temperatures in the western tropical Pacific may be contributing to some changes in weather patterns over the region. International climate models forecast ENSO-neutral for early 2020. When ENSO is neutral, it has a reduced effect on Australian and global climate, and other influences are more likely to dominate.

Cloudiness near the Date Line has generally remained below average since early to mid-September. Overall cloud patterns are consistent with neutral ENSO.

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

Cloudiness in the eastern tropical Indian Ocean has been well below average, while cloudiness is well above average in the western Indian Ocean. This is consistent with the presence of a positive Indian Ocean Dipole.

Trade winds for the 5 days ending 8 December were close to average across the central and eastern tropical Pacific, stronger than average just on the Date Line, and weaker than average to the west of the Date Line. The pattern of winds in the west is likely associated with a low pressure centre to the east of Papua New Guinea.

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.

In the Indian Ocean, trade winds have generally been much stronger than average over the past few months, typical of a strong positive IOD phase.

All eight surveyed international climate models indicate central tropical Pacific sea surface temperatures in the NINO3.4 region will remain at ENSO-neutral levels into early autumn 2020.

One model indicates that values may move towards La Niña thresholds during autumn, surpassing the threshold value during April. The remaining models all maintain NINO3.4 values within the neutral range throughout the outlook period.

Sea surface temperatures (SSTs) for November were warmer than average across much of the equatorial Pacific Ocean.

SSTs were warmer than average in much of the Tasman Sea and around Western Australia. SSTs were mostly close to average around the rest of Australia, though there were cool anomalies in some areas of the Coral Sea and in waters to the south of Australia.

The November values for NINO3 were +0.5 °C, NINO3.4 +0.6 °C, and NINO4 +0.9 °C. All three NINO indices warmed compared to October.

The 30-day Southern Oscillation Index (SOI) for the 30 days ending 8 December was −5.3. The 90-day value was −7.5. The 30-day SOI values have moved closer to neutral over the past 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.

It is likely that atmospheric pressure at Darwin, and hence values of the SOI, during 2019 have been influenced by the very strong positive IOD as well as by patterns in the Pacific.

The Indian Ocean Dipole (IOD) remains positive, although IOD index values continue to decline. The latest weekly value to 8 December was +0.86 °C.

The strong temperature gradient across the Indian Ocean has begun to ease. SSTs in the west of the basin remain warmer than average, but have cooled slightly compared to two weeks ago, while in the east of the basin SSTs have warmed and cool anomalies have almost disappeared from the region to the south of Indonesian island of Sumatra. The overall pattern of sea surface temperatures has remained generally consistent with a positive IOD pattern since late May.

Five of the six international climate models surveyed by the Bureau indicate the IOD will remain positive into January. All of the models anticipate IOD values with continue to decline from December into the new year.

While the IOD continues to show signs it will persist later than usual this year, it remains unlikely that the positive IOD will persist into the second half of summer. IOD events dissipate as the monsoon trough moves into the southern hemisphere, which changes the broadscale wind patterns over the IOD region and returns sea surface temperatures to near average.

The four-month sequence of equatorial sub-surface temperature anomalies (to November) shows cool anomalies in the western to central equatorial Pacific, at a depth of around 100 to 200 m. Weak warm anomalies extend across most of the top 100 m of the equatorial Pacific.

Warm anomalies in the central Pacific intensified in October, compared to September and August, but have decreased for November. Cool anomalies extend further east now than they did for October.

For the five days ending 9 December water temperatures were close to average across most of the sub-surface of the eastern equatorial Pacific, while in the west areas between 75 m and 200 m depth were somewhat warmer than average, reaching more than 3 degrees warmer than average for this time of year in a small pocket.