ENSO Wrap-Up
Current state of the Pacific and Indian oceans

For the week ending 2 July, sea surface temperatures (SSTs) were slightly warmer than average across most of the equatorial Pacific Ocean. Generally weak warm anomalies are also present across much of the South Pacific, including areas immediately south of the equator.

The NINO3.4 SST anomaly has remained at around +0.5 °C since mid-April, while NINO3 and NINO4 both warmed slightly to +0.4 °C and +0.6 °C respectively.

The tropical Pacific Ocean is currently neutral. Most climate models indicate the Pacific is likely to remain ENSO neutral for the remainder of 2017. This means the Bureau’s ENSO Outlook is currently INACTIVE, with neither El Niño nor La Niña expected to influence Australia’s climate this year.

Although the tropical Pacific Ocean is slightly warmer than usual, this warmth is within the ENSO neutral range. The Southern Oscillation Index (SOI) has recently been negative due to higher than normal atmospheric pressure in the Australian region, but all other ENSO indicators are at neutral levels.

In the tropical Indian Ocean, the Indian Ocean Dipole (IOD) is also neutral, with no sign of either negative IOD or positive IOD present in the ocean or atmosphere. However, some climate models suggest a positive IOD could develop in the coming months. Positive IOD events are typically associated with below average winter and spring rainfall over central and southern Australia.

Cloudiness near the Date Line is slightly below average. Cloudiness has been fluctuating around average for the past three months, though has tended towards less cloud than average overall.

Equatorial cloudiness near the Date Line typically increases during El Niño (below average OLR) and decreases during La Niña (above average OLR).

Trade winds for the 5 days ending 2 July were near average over the tropical Pacific.

During La Niña events, there is a sustained strengthening of the trade winds across much of the tropical Pacific, while during El Niño events there is a sustained weakening, or even reversal, of the trade winds.

Seven of eight international climate models surveyed by the Bureau indicate that ENSO-neutral conditions are likely for the second half of 2017.

However, while the likelihood of El Niño developing in the coming months is low, climate outlooks for winter suggest below average rainfall for southeastern and southwestern Australia, combined with warmer than average days.

SST anomalies for June show sea surface temperatures were slightly warmer than average across most of the equatorial Pacific Ocean. Weak warm anomalies were present across most of the Pacific south of the equator, including around Australia, and also warmer than average in waters around southern and western Australia, to the north of the Maritime Continent, and across large parts of the North Pacific between about 20 and 30°N.

The June values for the NINO3.4, NINO3 and NINO4 regions were +0.5 °C, +0.3 °C and +0.5 °C, respectively.

The 30-day Southern Oscillation Index (SOI) to 2 July was −10.0 (90-day value −5.5). Values have dropped steadily over the past two weeks, and are currently within El Niño territory, but it remains to be seen if this will be sustained.

Sustained positive values of the SOI above +7 typically indicate La Niña while sustained negative values below −7 typically indicate El Niño. Values between about +7 and −7 generally indicate neutral conditions.

The Indian Ocean Dipole (IOD) is neutral. The weekly index value to 2 July was −0.25 °C.

Three out of six climate models predict a positive IOD will develop during late winter to early spring.

A positive IOD typically brings below average winter–spring rainfall to parts of southern and central Australia.

The four-month sequence of sub-surface temperature anomalies (to June) shows water temperatures in the sub-surface of the equatorial Pacific Ocean were generally near average. Areas of weak warm anomalies persist in the top 150 m of the tropical Pacific west of 160°E, while an area of weak cool anomalies was present at around 150 m depth to the east of the Date Line.

The sub-surface temperature map for the 5 days ending 2 July shows temperatures were generally close to average across the equatorial Pacific Ocean. Cool anomalies at a depth of 100 to 200 m in the central Pacific have continued to weaken, although a small area remains more than 3 degrees cooler than average.