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

The SST map for May shows SSTs were close to average across most of the equatorial Pacific Ocean, although cool anomalies remained in some small areas of the tropics in the east of the Basin, extending along the coastline of South America. These cool anomalies have weakened compared to April.

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

May values of the three key NINO indices were: NINO3 −0.2 °C, NINO3.4 −0.1 °C, and NINO4 +0.1 °C.

Sea surface temperatures (SST) for the tropical Pacific Ocean for the week ending 20 June 2021 were close to average across the equatorial Pacific Ocean.

Warm anomalies have increased in the western Pacific, with warmer than average SSTs extending across waters 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 20 June were: NINO3 +0.3 °C, NINO3.4 + 0.2 °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 20 June was −2.7. The 90-day SOI value was +2.2. 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 20 June 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 and indiscernible. Most climate models suggest the MJO will re-emerge briefly in the African region, with the possibility it may move into the Indian Ocean during July. However, the MJO is unlikely to have significant influence on Australian rainfall at this time of year.

The Indian Ocean Dipole (IOD) index has been below the negative IOD threshold (−0.4 °C) for five consecutive weeks. The latest weekly value of the IOD index to 20 June was −0.70 °C.

While a negative IOD event is not declared until the index remains below the threshold for at least 8 weeks, this pattern can still influence Australian rainfall as the event develops, with wetter than average conditions in central and southern Australia more likely.

Most of the five surveyed climate models anticipate values of the IOD index will remain within negative thresholds into the middle of spring. Four of five models predict negative IOD will persist until October, with two of these continuing into November.

Weekly sea surface temperatures (SSTs) in the Indian Ocean were warmer than average across much of the southern and eastern halves of the basin, while small areas of cooler than average SSTs around the Horn of Africa and the Arabian Peninsula have strengthened compared to two weeks ago.

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 17 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 west, and close to the surface in the top 100 m depth east of 140°W.

For the five days ending 20 June, sub-surface temperatures were close to average across most of the equatorial Pacific, consistent with an ENSO neutral state. Warm anomalies in excess of 2 °C exist between the depths of 25 m and 100 m in the eastern Pacific. There has been very little change compared to two weeks ago.

The Indian Ocean Dipole (IOD) index has been below the negative IOD threshold for the past five weeks, with no models forecasting a rise in the index any time soon. Large parts of the eastern Indian Ocean are now warmer than average, with cooler than average waters near the Horn of Africa—a pattern typical of a negative IOD. Four of the five climate models surveyed by the Bureau predict a negative IOD for the second half of the southern hemisphere winter and into spring.

A negative IOD event is declared when there have been at least eight weeks below the IOD index threshold of −0.4 °C. Negative IOD conditions increase the chances of above average winter–spring rainfall for parts of southern Australia.

The El Niño–Southern Oscillation (ENSO) remains neutral with all oceanic and atmospheric indicators within the neutral range. Most climate model outlooks indicate this neutral ENSO state is likely to continue for the southern hemisphere winter and early spring, with tropical Pacific sea surface temperatures slowly cooling over the coming six months. This cooling pattern may be partly contributing to the wetter than average climate outlooks for parts of eastern Australia.

The Southern Annular Mode (SAM) has been positive for the past fortnight. Forecasts suggest SAM will return to neutral levels for the coming fortnight. 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.

The Madden–Julian Oscillation (MJO) is currently weak or indiscernible. Most climate models suggest the MJO will re-emerge briefly in the African region. At this time of the year, the MJO influence is primarily in the northern hemisphere, and it therefore has less influence on northern Australia.

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 coming days, and then remain 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 winter, with one model reaching the La Niña threshold during September, and two of the seven models indicating the possibility of La Niña in late spring.

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