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

The SST map for June 2021 shows SSTs were close to average across most of the equatorial Pacific Ocean, although SSTs over the eastern Pacific Ocean warmed slightly resulting in a small region of warm anomalies off the coast of Ecuador and a reduction of cool anomalies present in May.

SSTs were warmer than average in waters around the west and much of the south of Australia.

June 2021 values of the three key NINO indices were: NINO3 0.2 °C, NINO3.4 0.2 °C, and NINO4 +0.2 °C.

Sea surface temperatures (SST) for the tropical Pacific Ocean for the week ending 4 July 2021 were close to average across the equatorial Pacific Ocean.

Warmer than average SSTs continue over the western Pacific Ocean south of the equator, parts of the Maritime Continent, across the Tasman Sea, and around the coast of Australia.

All three NINO indices are within the ENSO-neutral range. The latest values of the three NINO indices in the tropical Pacific for the week ending 4 July 2021 were: NINO3 +0.3 °C, NINO3.4 + 0.3 °C, and NINO4 +0.2 °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 30-day Southern Oscillation Index (SOI) for the 30 days ending 4 July was +5.1. The 90-day SOI value was +2.8. Both are within ENSO-neutral thresholds.

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.

Trade winds for the 5 days ending 4 July were close to average across the tropical 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.

The Madden–Julian Oscillation (MJO) is currently weak to moderate in strength. Most climate models suggest the MJO will weaken and approach the Maritime Continent over the next fortnight. This can have the effect of increasing westerly wind anomalies over the Indian Ocean, reinforcing the negative IOD.

The latest weekly value of the Indian Ocean Dipole (IOD) index to 4 July was −0.27 °C. The IOD index has been below the negative IOD threshold (−0.4 °C) for six consecutive weeks prior to this week.

While a negative IOD event is not declared until the index has been below the threshold for at least 8 weeks, this pattern can still influence Australian rainfall as the event develops.

Three of the models forecast development to occur during winter with another one indicating development in early spring. Most of the five surveyed climate models anticipate values of the IOD index will remain within negative thresholds into the middle of spring.

Weekly sea surface temperatures (SSTs) in the Indian Ocean were warmer than average across much of northern and eastern halves of the basin. SSTs around the Horn of Africa and the Arabian Peninsula have warmed slightly.

A negative IOD, and a warmer eastern Indian Ocean generally, increase the chances of above average winter–spring rainfall for parts of southern Australia.

Cloudiness near the Date Line has fluctuated around the mean since the start of April. While generally remaining close to average, cloudiness has been slightly less than average (positive OLR anomalies) during June.

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

The four-month sequence of equatorial Pacific sub-surface temperature anomalies (to June) shows a pattern consistent with a neutral ENSO state. Weak warm anomalies were present across much of the column depth from the Date Line westwards, and also close to the surface in the top 100 m depth east of 140°W.

For the five days ending 4 July, a layer of weak warm anomalies existed above very weak cool anomalies. Warm anomalies in excess of 2 °C exist between the depths of 25 m and 75 m in the eastern Pacific. There has been little change compared to two weeks ago. The strength of the anomalies is consistent with an ENSO neutral state.

Indian Ocean Dipole (IOD) index values continue to be negative. A negative IOD event is declared when there have been at least 8 weeks below the IOD index threshold of −0.4 °C. A negative IOD increases the chances of above average winter-spring rainfall for parts of southern Australia.

The most recent weekly IOD value is −0.27 °C, which is above the negative IOD threshold (−0.4 °C) but follows on from the IOD index being below the negative IOD threshold for the previous six weeks. Most climate models surveyed by the Bureau predict the IOD to return to below the negative IOD threshold, with a negative IOD event likely for the second half of the southern hemisphere winter and into spring.

The El Niño–Southern Oscillation (ENSO) remains neutral with most oceanic and atmospheric indicators within the neutral range. Cloudiness near the Date Line has been below average over the past fortnight, although this is weak and a localised pattern. Most climate model outlooks indicate a neutral ENSO state is likely to continue for the remainder of the southern hemisphere winter and spring despite tropical Pacific sea surface temperatures slowly cooling over the coming six months. This may be contributing to the wetter than average climate outlooks for parts of Australia.

The Southern Annular Mode (SAM) has been positive for the past four weeks. Forecasts suggest SAM will return to neutral levels over the coming week. Neutral SAM has little influence on Australian climate, while positive SAM typically means cold fronts and troughs are shifted further south than their usual winter path.

It is likely some of the wetter weather seen during June may have been a result of the developing negative IOD event, while the drier weather for parts of southern WA and western Tasmania may have been influenced by the positive SAM.

The Madden–Julian Oscillation (MJO) is currently over the Indian Ocean. Most climate models indicate the MJO will weaken approaching the Maritime Continent over the coming week. Should the MJO maintain its strength, an MJO near the Maritime Continent typically leads to stronger westerly winds over the Indian Ocean, which can reinforce the negative IOD.

Climate change continues to influence Australian and global climate. Australia's climate has warmed by 1.44 ± 0.24 °C over 1910–2019, while southern Australia has seen a reduction of 10–20% in cool season (April–October) rainfall in recent decades.

The Southern Annular Mode (SAM) index is strongly positive at present. SAM is expected to weaken to neutral levels over the coming week, and then remain close to neutral over the next two weeks.

At this time of year positive SAM typically results in cold fronts and storm tracks shifting further south than their usual winter path. This can increase rainfall over parts of eastern Australia, but reduce rainfall for much of south-east South Australia, western and central Victoria, Tasmania, and the west coast of Western Australia.

The El Niño–Southern Oscillation (ENSO) is currently neutral. All of the international climate models surveyed by the Bureau anticipate NINO3.4 will remain neutral during winter despite temperatures gradually cooling over the coming months. Two models forecast temperatures reaching the La Niña threshold during September.

This shift towards cooler forecast values of NINO3.4 may be contributing to the wetter than average rainfall outlooks for parts of the country.