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

Sea surface temperature (SST) anomalies for the week ending 12 May were warmer than average across nearly the entire tropical Pacific Ocean. Compared to two weeks ago, the surface of the ocean has warmed slightly in the west and cooled slightly in the east — a weakening of the typical El Niño pattern. Most of the tropical Pacific region is half to one degree warmer than average.

Waters are also warmer than average across much of the southern Pacific Ocean, particularly across areas south of 30°S. SSTs are up to two degrees warmer than average over a broad area extending across the Tasman Sea, along the New South Wales coast, and well to the east of New Zealand. Waters around the rest of Australia are generally close to average temperatures, although weak cool anomalies are present to the southwest of Australia and in the west of the Great Australian Bight.

The latest values of the three key NINO indices in the tropical Pacific for the week ending 12 May are: NINO3 +0.7 °C, NINO3.4 +0.7 °C and NINO4 +0.7 °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.

Indicators have been close to El Niño thresholds over the past several months, but signs have emerged of a weakening of these patterns. As a result, the Bureau's ENSO Outlook has been downgraded to El Niño WATCH. This means the chance of El Niño developing in 2019 is approximately 50%, which is still double the normal likelihood.

While sea surface temperatures in the tropical Pacific Ocean remain close to El Niño levels, water beneath the surface has slowly cooled over the past few months. Atmospheric indicators such as the Southern Oscillation Index (SOI) and cloudiness near the Date Line have generally remained in the neutral range, despite short-term El Niño-like SOI values in the last fortnight.

International models surveyed by the Bureau indicate that sea surface temperatures in the tropical Pacific are likely to remain near El Niño thresholds until mid-winter, before cooling in late winter to spring. By August, two of the eight models are clearly at El Niño levels, with another two near El Niño thresholds.

El Niño typically brings drier than average conditions for eastern Australia during winter–spring, and warmer days across the southern two-thirds of the country.

The Indian Ocean Dipole (IOD) is currently neutral. However, models show a tendency towards positive IOD values during the forecast period, with five of six models suggesting a positive IOD event is likely to develop in winter, and persist into mid-spring.

Cloudiness near the Date Line has been generally above average since early December, however, values have fluctuated closer to average 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 12 May are close to average to the west of the Date Line. The weakened trade winds in the western Pacific are likely tied in with the current passage of the Madden-Julian Oscillation, and could temporarily warm parts of the tropical Pacific Ocean again. 

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.

While most climate models forecast El Niño-like warmth to persist the early austral winter, the ocean is forecast to cool over late winter and spring.

While seven of eight surveyed climate models anticipate El Niño thresholds will be met for June, for August and September two models remain in El Niño territory and two are at borderline values, with the remaining four models indicating neutral conditions are most likely.

Note that model accuracy when forecasting through the autumn months is lower than at other times of the year, due to the natural cycle of ENSO. Forecast accuracy improves for outlooks issued in June.

Sea surface temperatures (SSTs) for April were warmer than average across most of the tropical Pacific Ocean. Temperature anomalies in many areas had decreased slightly compared to March.

A significant area of warmer than average SSTs were present surrounding southeast Australia, extending across the Tasman Sea and well to the east of New Zealand; temperatures were up to two degrees warmer than average in much of this region. Waters were also warmer than average in coastal waters of much of the Great Australian Bight, while areas of cool anomalies were present to the southwest of Australia.

The March values for NINO3 were +0.7 °C, NINO3.4 +0.7 °C, and NINO4 +0.6 °C, with values for both the central and western regions cooler than for March.

The 30-day Southern Oscillation Index (SOI) remains neutral. The SOI value for the 30 days to 12 May was −6.2, while the 90-day average was −8.3.

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) is currently neutral. The latest weekly index value to 12 May is +0.06 °C.

All six of the international climate models surveyed by the Bureau indicate that the IOD will be positive for June. For July, one model drops back to neutral, but the other five models forecast positive IOD values to persist through to at least the end of the outlook period (October).

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 April) shows that although the sub-surface of the tropical Pacific has continued to cool, weak positive anomalies persist across most of the top 100 m of the sub-surface. Below 100 m depth, cool anomalies have strengthened, and some parts of the sub-surface are up to three degrees cooler than average.

Temperatures for the five days ending 12 May show waters were warmer than average in the shallow sub-surface of the eastern equatorial Pacific, with waters in much of the top 50 m east of 130°W more than two degrees warmer than average. Compared to two weeks ago, warm anomalies in this area have reduced.

Elsewhere temperatures were close to average, although there are some small pockets of cool anomalies more than two degrees cooler than average in the deeper sub-surface in the east, and at around 200 m depth near the Date Line.