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

El Niño consolidates

Issued on 23 June 2015 |

The 2015 El Niño continues to strengthen. Central and eastern tropical Pacific Ocean sea surface temperature indices are more than 1 °C above average for the sixth consecutive week. International climate models surveyed by the Bureau of Meteorology indicate further consolidation is likely. El Niño events typically strengthen during the second half of the year, reaching full strength during late spring or early summer. It is not possible at this stage to determine how strong this El Niño will be.

El Niño is typically associated with below-average winter and spring rainfall over eastern Australia and above-average daytime temperatures over the southern half of the country during the second half of the year. The strength of an El Niño does not always determine the strength of its effects on Australia's climate. There are examples of weak El Niño events resulting in widespread drought and strong El Niño events with little impact on rainfall.

The Indian Ocean Dipole (IOD) is currently neutral. Of the five international models that provide IOD outlooks, three suggest a positive IOD is likely during the southern spring. A positive IOD is typically associated with reduced winter and spring rainfall over parts of southern and central Australia.

Next update expected on 7 July 2015 | print version

Weekly sea surface temperatures

Over the past fortnight, sea surface temperature (SST) anomalies have increased in the eastern equatorial Pacific. Warm anomalies extend along the equator from the South American coastline to just west of the Date Line, with anomalies for the week ending 21 June in excess of +2 °C in much of the eastern equatorial Pacific.

All five NINO indices again exceeded +1 °C this week. It is unusual to have such a broad extent of warmth across the tropical Pacific; the last time this occurred was during the 1997–98 El Niño.

Warm anomalies persist across most of the northeast of the Pacific Basin, extending down the western coastline of North America and into South America. Warm anomalies are also present in areas to Australia's west, and across much of the Indian Ocean.

Click to see full-size map showing temperature anomalies in the tropical Pacific
Baseline period 1961–1990.
Index Previous Current Temperature change
(2 weeks)
NINO3 +1.5 +1.7 0.2 °C warmer
NINO3.4 +1.3 +1.4 0.1 °C warmer
NINO4 +1.2 +1.1 0.1 °C cooler
Monthly sea surface temperatures

The SST anomaly map for May 2015 shows positive anomalies across the equatorial Pacific. These positive anomalies extend from the South American coastline, and past the International Date Line to around 160°E. The northeast Pacific Ocean continues to remain above average, while SST anomalies surrounding Australia cooled compared to April, with May anomalies in the Australian region generally close to average. All five NINO indices averaged over the month were greater than +1 °C, which again has not occurred since the 1997–98 El Niño.

Click to see full-size map showing temperature anomalies in the tropical Pacific
Baseline period 1961–1990.
Index April May Temperature change
NINO3 +0.8 +1.2 0.4 °C warmer
NINO3.4 +0.8 +1.1 0.3 °C warmer
NINO4 +1.1 +1.1 no change
5-day sub-surface temperatures

The sub-surface temperature map for the 5 days ending 21 June shows temperatures are cooler than average below the surface of the ocean in the western equatorial Pacific and warmer than average in the top 150 m of the central to eastern equatorial Pacific. Water in the top 75 m of the far eastern Pacific is more than 5 °C warmer than average. This general pattern is consistent with El Niño.

Compared to two weeks ago, the area of warm anomalies in the eastern equatorial Pacific sub-surface has contracted while the area of cool anomalies in the west has increased.

Monthly sub-surface temperatures

The four-month sequence of sub-surface temperature anomalies (to 22 June) shows a generally similar pattern has been maintained in June so far as was present for May and April, although the strength of warm anomalies has increased across the three month period.

For June to date, warm anomalies are evident 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 persist in the sub-surface of the western equatorial Pacific.

Southern Oscillation Index

The Southern Oscillation Index (SOI) has risen over the past two weeks, although this return to neutral values is expected to be temporary and results from local weather factors rather than a change in the broadscale pattern.

The latest 30-day SOI value to 21 June was +0.7. The 90-day SOI remains within El Niño territory, indicating persistent higher atmospheric pressure in the western Pacific at the three-month timescale.

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 over the western half of the tropical Pacific were weaker than average for the 5 days ending 21 June. Trade winds have been consistently weaker than average, and on occasion reversed in direction, since the start of 2015.

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

Cloudiness near the Date Line

Cloudiness near the Date Line has returned to above-average values during the past two weeks. Cloudiness has been generally above average since the start of March, with brief forays into slightly below average values at the end of May and start of June.

Cloudiness along the equator, near the Date Line, is an important indicator of ENSO conditions, 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 late 2015.

Click to see full-size map of NINIO3.4 SST plumes from POAMA forecasts, updated daily.
Indian Ocean Dipole

The Indian Ocean Dipole (IOD) is currently neutral. The latest weekly value of the IOD index to 21 June is −0.07 °C. 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 or spring.

Positive IOD events, often associated with lower rainfall in central and southeastern Australia, are more likely to occur during El Niño. Approximately 50% to 60% of the time that El Niño has developed in the past, a positive IOD has also developed. Positive IOD events are often associated with lower rainfall in central and southeastern Australia. Conditions will be monitored closely.

Click to see full-size map of IOD SST plumes from POAMA forecasts, updated daily.

See also: IOD forecasts