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

Sea surface temperatures (SSTs) for the week ending 23 June remain warmer than average across much of the equatorial Pacific Ocean, although some areas of the eastern equatorial Pacific have returned to near average temperatures.

Waters are also warmer than average across much of the southwest Pacific, including around the east and southeast of Australia. Sea surface temperatures around the remainder of Australia are broadly close to average, with weak negative anomalies along parts of the western and southern coastline.

The latest values of the three key NINO indices in the tropical Pacific for the week ending 23 June are: NINO3 +0.4 °C, NINO3.4 +0.6 °C and NINO4 +0.7 °C. All three have cooled compared to two weeks ago.

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 immediate likelihood of El Niño developing has passed, meaning the ENSO Outlook has been reset to INACTIVE. While the possibility of El Niño can't be completely ruled out for 2019, the tropical Pacific Ocean is more likely than not to remain in an ENSO-neutral phase over the coming months. Model outlooks indicate a positive Indian Ocean Dipole is likely to drive Australia's weather for much of the rest of 2019, meaning the likelihood of a drier than average winter–spring remains.

Oceanic and atmospheric indicators are now largely at ENSO-neutral levels. Tropical Pacific sea surface temperatures have cooled over the past fortnight but remain slightly warmer than average. Cloudiness near the Date Line and trade winds have been close to neutral over recent weeks, while the Southern Oscillation Index (SOI) has hovered around El Niño threshold values over the past month. With little anomalous warmth in the ocean sub-surface, most climate models indicate the tropical Pacific will continue shifting further away from El Niño thresholds through the winter.

In the Indian Ocean, waters remain average to cooler than average in eastern parts, and warmer than average further west; a pattern typical of a positive Indian Ocean Dipole (IOD). While the IOD index fell below the positive IOD threshold this week, climate models indicate this is likely to be temporary, with positive IOD values forecast to persist through winter and into spring. Typically, a positive IOD brings below average winter-spring rainfall, above average temperatures, and an earlier start to the fire season for southern and central Australia.

Cloudiness near the Date Line has fluctuated around average values since late April.

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 5 days ending 23 June were close to average across most of the tropical Pacific, and weaker than average over a small area of the western 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 latest weekly NINO3.4 value to 23 June is +0.6 °C, which is 0.2 °C below the El Niño threshold. Similarly, NINO3 values have cooled to +0.4 °C, while NINO4 is +0.7 °C. Most climate models predict the tropical Pacific Ocean will continue to cool, with all eight surveyed climate models anticipating ENSO-neutral values during the late austral winter and spring.

Considering that current NINO index values are neutral, indicators in both atmosphere and ocean continue to ease, and model outlooks favour an ENSO-neutral state for the coming months, the Bureau ENSO Outlook has been reset to INACTIVE.

SSTs for May were warmer than average across most of the tropical Pacific Ocean. Temperature anomalies in some areas decreased slightly from April.

SSTs show a broad area of warmer than average water surrounds southeast Australia, extending across the Tasman Sea and well to the east of New Zealand; temperatures are up to two degrees warmer than average in much of this region. Much of the rest of the Australian region SSTs are close to normal, but weak negative anomalies are present to the southwest of Australia.

The May values for NINO3 were +0.7 °C, NINO3.4 +0.7 °C, and NINO4 +0.6 °C, with values holding steady compared to April.

The 30-day Southern Oscillation Index (SOI) has remained near El Niño threshold levels over the past two weeks, while 90-day values have remained neutral. The SOI for the 30 days ending 23 June was −8.7, with the 90-day value −5.6.

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) index has dipped into neutral values during the last week, while the overall pattern remains positive. The latest weekly index value to 23 June is +0.26 °C.

However, the positive IOD-like SST pattern in the Indian Ocean remains. Surface waters in the central to western Indian Ocean are warmer than average, while in the east, cool anomalies are present south of the Indonesian island of Java, extending eastward to the island of Sumba. The latest fall in the IOD values is simply due to average to cooler than average waters right on the African coastline, most likely generated in association with severe tropical cyclone Vayu. This means the strongest anomalies are just outside the boxes used to calculate the IOD index (see map of IOD regions).

Five of the six international climate models surveyed by the Bureau indicate positive IOD values are likely to continue through the austral winter and spring, suggesting a positive IOD event may be underway. To be considered a positive IOD event, values above the positive threshold (+0.4 °C) would need to be sustained for at least eight weeks.

A positive IOD often results in below average winter–spring rainfall over southern and central Australia.

The four-month sequence of equatorial sub-surface temperature anomalies (to 20 June) shows a pattern of very weak shallow warm anomalies, and very weak cool anomalies at greater depth — a pattern which has been evident, although progressively weakening, since April.

Weak positive anomalies persist across most of the top 100 m of the sub-surface, with most of this region within one and a half degrees of average. In areas of both the east and west below 100 m depth, weak cool anomalies persist, with anomalies up to one degree cooler than average in the east and mostly less than two degrees cooler than average in the west.

Temperatures for the five days ending 23 June show waters are within one degree of average temperatures across nearly the entire sub-surface of the equatorial Pacific. Compared to two weeks ago, very weak warm anomalies in the shallow sub-surface and very weak cool anomalies below 100 m depth have weakened further, with only very small volumes of water remaining more than two degrees warmer or cooler than average.