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

The SST map for July 2021 shows SSTs were close to average across most of the equatorial Pacific Ocean, although warmer than average SSTs continued in the eastern Pacific Ocean close to South America.

SSTs were warmer than average in waters around the north and south-east of Australia.

Values of the three key NINO indices for July 2021 were: NINO3 +0.1 °C, NINO3.4 +0.0 °C, and NINO4 +0.1 °C.

Sea surface temperatures (SST) for the tropical Pacific Ocean for the week ending 1 August 2021 were close to average across the majority of the equatorial Pacific Ocean, with warmer than average SSTs in the east close to South America.

Warmer than average SSTs continue over the far western Pacific Ocean, including parts of the Maritime Continent, around the coast of northern and eastern Australia, and across the Tasman Sea.

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 1 August 2021 were: NINO3 0.0 °C, NINO3.4 −0.1 °C, and NINO4 +0.1 °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 1 August 2021 was +15.1. The 90-day SOI value was +8.5.

The 30-day value has remained similar over the past few weeks, with some pressure patterns showing La Niña-like characteristics, although it is possible some of this pressure influence may be coming from the Indian Ocean.

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 30 July 2021 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 active over the Western Hemisphere, and is expected to remain at moderate or weak strength as it progresses eastwards across Africa during the next week.

It is unlikely the MJO will influence Australia rainfall patterns during the next fortnight. Farther afield, when the MJO is near Africa it typically means below average cloudiness and rainfall across much of much of India and parts of south-east Asia.

A negative IOD event is underway.

The latest weekly value of the Indian Ocean Dipole (IOD) index to 1 August 2021 was −0.76 °C. The IOD index has generally been below the negative IOD threshold (−0.4 °C) since mid-May.

Four of the five international climate models surveyed by the Bureau anticipate the IOD index will remain within negative thresholds through spring, with four of five models then returning to neutral values after November.

Weekly sea surface temperatures (SSTs) in the Indian Ocean were warmer than average across much of the eastern half of the basin. SSTs around the Horn of Africa and the Arabian Peninsula have cooled again, with cool anomalies strengthening close to the coastline.

A negative IOD, and a warmer eastern Indian Ocean generally, increase the chances of above average winter–spring rainfall for parts of southern and eastern Australia. Negative IOD also makes below average maximum temperatures more likely across southern Australia, while maximum and minimum temperatures are more likely to be above average for the northern tropics of Australia.

Cloudiness near the Date Line has generally been close to or slightly below average (positive OLR anomalies) since April, and tended to be a little more consistently below average during June and the first half of July.

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 July) shows a pattern consistent with a neutral ENSO state. Weak warm anomalies were present across much of the column depth west of the Date Line, while weak cool anomalies were present across the central and eastern equatorial Pacific between around 175 m depth and 75 m depth. These cool anomalies developed during July. 

For the five days ending 30 July, sub-surface temperatures were close to average across most of the equatorial Pacific, although a region of cooler than average water has emerged in the sub-surface of the central equatorial Pacific. Anomalies reach more than three degrees cooler than average around 150 m depth between 160°W and 145°W.

Overall, the subsurface remains consistent with an ENSO neutral state.

The negative Indian Ocean Dipole (IOD) event continues. A negative IOD increases the chances of above average winter–spring rainfall for much of southern and eastern Australia. It also increases the chances of cooler than average days in southern Australia for winter–spring, and warmer than average nights across northern Australia.

The most recent weekly IOD index value is −0.76 °C, with warmer than average waters in the eastern tropical Indian Ocean, and average to cooler than average waters in the western tropical Indian Ocean. Most climate models surveyed by the Bureau predict negative IOD conditions are likely to persist throughout spring.

The El Niño–Southern Oscillation (ENSO) remains neutral with most oceanic and atmospheric indicators within the neutral range. While pressure patterns show some La Niña-like characteristics, as indicated by the latest Southern Oscillation Index (SOI) 30-day value of +15.1, it is likely that some of this shift in pressure is driven from warm conditions in the eastern Indian Ocean. Most climate model outlooks indicate the central tropical Pacific is likely to cool over the coming months, with three of seven models surveyed by the Bureau indicating this cooling will be enough to reach La Niña thresholds in spring, with the remaining four models staying neutral. Along with the negative IOD, this may be contributing to the wetter than median climate outlooks in Australia

The Southern Annular Mode (SAM) index has recently been positive, but is forecast to return to neutral levels in the coming days, and remain so for at least the next fortnight. A neutral SAM has little influence on Australian climate.

The Madden–Julian Oscillation (MJO) is currently in the Western Hemisphere. Most climate models indicate the MJO will move towards Africa over the coming week, although climate models indicate the strength of the MJO could range from moderate to weak. An MJO near Africa typically means below average cloudiness and rainfall across much of much of India and parts of southeast Asia.

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 currently positive, but it expected rapidly return to neutral values over coming days and remain so for the remainder of this fortnight.

A neutral SAM has little influence on Australian climate.

The El Niño–Southern Oscillation (ENSO) is currently neutral. Most of the international climate models surveyed by the Bureau anticipate NINO3.4 will cool during the coming months, but vary in how much cooling they expect. Three of the seven surveyed models anticipate NINO3.4 will meet or exceed La Niña thresholds from October through December. The remaining four models predict a neutral ENSO pattern to continue through to the end of 2021.

La Niña typically enhances spring rainfall in northern and eastern Australia, and the shift towards cooler forecast values of NINO3.4 may be contributing to the wetter than average rainfall outlooks for parts of the country.