Current state of the Pacific and Indian Ocean
El Niño to persist into early 2016
Issued on 4 August 2015 | Product Code IDCKGEWW00
The 2015 El Niño is now well-established and continues to strengthen. In the coming weeks, the central tropical Pacific Ocean (the NINO3.4 region) may exceed the peak values reached during the 2002 and 2009 El Niño events, but current anomalies remain well short of the 1982 and 1997 peaks. Note that peak values are normally recorded late in the year. Trade winds remain weakened and are likely to contribute to more warming of the tropical Pacific Ocean. Other indicators such as cloudiness near the Date Line, the Southern Oscillation Index, and sub-surface temperatures in the tropical Pacific Ocean remain typical of an established El Niño.
International climate models surveyed by the Bureau of Meteorology all indicate that El Niño will continue to strengthen, and persist into early 2016. Typically, El Niño peaks during the late austral spring or early summer, and weakens in the following year.
El Niño is usually associated with below-average winter–spring rainfall over eastern Australia and above-average daytime temperatures over the southern half of the country. However, El Niño is not the only influence on rainfall and temperature; other factors, such as sea surface temperatures to the north of Australia and in the Indian Ocean, also affect Australia's climate.
The Indian Ocean Dipole (IOD) remains neutral. A positive IOD event remains possible, with three of the five international models indicating a positive IOD is likely during late winter to spring. A positive IOD is typically associated with reduced winter and spring rainfall over parts of southern and central Australia.
Next update expected on 18 August 2015 | print version
- Impact on rainfall:
- El Niño: average rainfall
- El Niño: past events
- La Niña: average rainfall
- La Niña: past events
- Weekly sea surface temperatures
Over the past fortnight, sea surface temperature (SST) anomalies have decreased slightly in the eastern equatorial Pacific. Warm anomalies persist along the equator from the South American coastline to about 160°E. Anomalies for the week ending 2 August exceeded +2 °C across nearly all of the eastern equatorial Pacific and smaller areas of the central Pacific.
All five NINO indices again exceeded +1 °C this week.
Warm anomalies are present across most of the northern half of the Pacific basin, except for parts of the northwest. The eastern half of the northern Pacific is more than one degree warmer than average, and two degrees warmer than average in places. Warm anomalies are also present along parts of the east coast of Australia, in areas to Australia's west, and across much of the Indian Ocean.
- Monthly sea surface temperatures
The SST anomaly map for July 2015 shows positive anomalies extended from the South American coastline, across the equatorial Pacific, past the Date Line to around 160°E. Compared to June, the strength of these anomalies have increased in the eastern Pacific. Strong warm anomalies also persisted across much of the northeast of the Pacific Basin, with weak warm anomalies to Australia's east, and moderate to strong warm anomalies across much of the Indian Ocean.
NINO3 measured its warmest monthly anomaly since the 1997–98 El Niño, with an anomaly of +1.9 °C for July 2015, ahead of +1.7 °C in June 2015 and +1.6 °C December 2009. The July 2015 value of NINO3.4 was +1.5 °C.
In the coming weeks, the NINO3.4 region may exceed the peak anomaly values reached during the 2002 (+1.6 °C) and 2009 (+1.7 °C) El Niño. The current El Niño has already exceeded the 2006 peak of +1.2 °C, but current anomalies still remain well short of the 1982 and 1997 peaks (+2.8 °C and +2.7 °C respectively). Note: peak values are typically recorded late in the year.
Baseline period 1961–1990. Index June July Temperature change NINO3 +1.6 +1.9 0.3 °C warmer NINO3.4 +1.3 +1.5 0.2 °C warmer NINO4 +1.1 +1.1 no change
- 5-day sub-surface temperatures
The sub-surface temperature map for the 5 days ending 2 August shows temperatures are warmer than average in the top 100 m of the central to eastern equatorial Pacific and cooler than average below the surface of the ocean in the western equatorial Pacific. Water in far eastern Pacific sub-surface is very much warmer than average, with anomalies around 75 m depth reaching more than 6 °C warmer than average. Warm anomalies in the east-central Pacific are somewhat stronger than they were two weeks ago.
Cool anomalies in the western equatorial Pacific remain similar to what they were two weeks ago, with a broad area more than 2 °C cooler than average between around 100 m and 200 m depth.
- Monthly sub-surface temperatures
The four-month sequence of sub-surface temperature anomalies (to June) shows a generally consistent pattern of anomalies throughout the past three months. Warm anomalies were evident for June across the top 100 m to 200 m of the equatorial Pacific sub-surface between about 160°E and the South American coast. Anomalies across large areas of the eastern half of the equatorial Pacific reached more than +4 °C. Cool anomalies persisted in the sub-surface of the western equatorial Pacific.
- Southern Oscillation Index
The Southern Oscillation Index (SOI) has risen somewhat over the past two weeks, but remains firmly within negative values. The 30-day SOI value to 2 August was −14.4.
Sustained positive values of the SOI above +7 may indicate La Niña, while sustained negative values below −7 may indicate El Niño. Values of between about +7 and −7 generally indicate neutral conditions.
- Trade winds
Trade winds for the 5 days ending 2 August show westerly anomalies were present over the western half of the equatorial Pacific. Trade winds were reversed (i.e. westerly winds) to the west of the Date Line.
Trade winds have been consistently weaker than average, and on occasion reversed in direction (i.e. westerly rather than easterly), since the start of 2015.
- Cloudiness near the Date Line
Cloudiness near the Date Line was above average during the second half of July and early August.
Cloudiness along the equator, near the Date Line, is an important indicator of ENSO, as it typically increases (negative OLR anomalies) near and to the east of the Date Line during El Niño and decreases (positive OLR anomalies) during La Niña.
- Model outlooks
All eight of the surveyed international climate models indicate the central Pacific Ocean will warm further during the coming months. All surveyed models indicate that NINO3.4 will remain above El Niño thresholds until at least the end of 2015.
- Indian Ocean Dipole
The Indian Ocean Dipole (IOD) is currently neutral. The weekly value of the IOD index to 2 August was −0.10 °C. Sea surface temperatures in the Indian Ocean are warmer than average over much of the basin.
Three of the five surveyed international climate models indicate a positive IOD event will occur during the southern hemisphere winter and spring.
Positive IOD events, often associated with lower rainfall in central and southeastern Australia, are more likely to occur during El Niño. Between 50% and 60% of all historical El Niño events have seen a positive IOD develop at the same time. Positive IOD events are often associated with lower rainfall in parts of central and southeastern Australia. Conditions will be monitored closely.
See also: IOD forecasts