Current state of the Pacific and Indian Ocean
Late season El Niño remains possible
Issued on Tuesday 23 September 2014 | Product Code IDCKGEWW00
Despite most ocean and atmospheric indicators falling short of El Niño thresholds, model outlooks and recent observations indicate that a late El Niño remains possible. The Bureau’s ENSO Tracker indicates there is at least a 50% chance of El Niño developing over the coming months, which is double the long-term likelihood.
The Southern Oscillation Index (SOI) has now remained negative for several weeks, and some renewed warming has occurred across the equatorial Pacific Ocean over the past fortnight. Both support the possibility of El Niño becoming established in the months ahead. Six of the eight international climate models surveyed by the Bureau indicate El Niño, or near-El Niño, conditions are likely for the southern summer.
El Niño is often associated with below-average rainfall over large parts of southern and eastern inland areas of Australia and above-average daytime temperatures over southern Australia. Such impacts can often occur while an event is developing, as experienced in some locations over the past several months.
The Indian Ocean Dipole (IOD) in the tropical Indian Ocean continues to show signs that it has returned to a neutral state. Waters to the north of Australia and in the Timor Sea are now at near-average temperatures. All climate models surveyed by the Bureau indicate the IOD will continue to weaken, with neutral conditions likely to become well established during the coming months.
Next update expected on 7 October 2014 | print version
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- Weekly sea surface temperatures
The ocean surface has warmed in the central tropical Pacific Ocean over the past two weeks while cooling in the far eastern tropical Pacific. Positive sea surface temperature (SST) anomalies are present along most of the equatorial Pacific (see SST anomaly map for the week ending 21 September). Warm anomalies also remain in areas of the southeastern Indian Ocean and across most of the northern Pacific Basin. Cool anomalies to the north and northwest of Australia have largely dissipated over the past fortnight.
- Monthly sea surface temperatures
The SST anomaly map for August shows the equatorial Pacific cooled somewhat around 120°W in the eastern Pacific and warmed across the western Pacific when compared to the preceding month. August SSTs were near-average across much of the central tropical Pacific and warmer than average elsewhere across the tropics, extending into the northern Pacific basic with warm anomalies also present to Australia’s northwest and extending into the Indian Ocean.
Baseline period 1961–1990. Index July August Temperature change NINO3 +0.7 +0.5 0.2 °C cooler NINO3.4 +0.2 +0.3 0.1 °C warmer NINO4 +0.4 +0.7 0.3 °C warmer
- 5-day sub-surface temperatures
The sub-surface temperature map for the 5 days ending 21 September shows temperatures across most of the equatorial Pacific sub-surface are near average, to slightly warmer than average in the eastern equatorial Pacific. As substantial areas of the central and eastern Pacific have low data coverage, as indicated by point observations (cross markings) on the image below, other sources of sub-surface data have also been considered.
- Monthly sub-surface temperatures
The four-month sequence of sub-surface temperature anomalies (to 22 September) shows that, for September to date, warm anomalies are present below 150 m depth in the western Pacific and across the shallow sub-surface from west of the Date Line to around 120°W. The sub-surface plot also shows areas of cool anomalies in the sub-surface of the far western and shallow eastern equatorial Pacific.
- Southern Oscillation Index
The Southern Oscillation Index (SOI) has hovered around −10 over the past fortnight. The latest approximate 30-day SOI value to 21 September is −10.1.
Sustained positive values of the SOI above +8 may indicate a La Niña event, while sustained negative values below −8 may indicate an El Niño event. Values of between about +8 and −8 generally indicate neutral conditions.
- Trade winds
Trade winds over the equatorial Pacific are near-average (see anomaly map for the 5 days ending 21 September).
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 of the trade winds.
- Cloudiness near the Date Line
Cloudiness near the Date Line has fluctuated around average during the past two weeks, but has generally been on the below average side, as has been the trend since the end of July.
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
Six of the eight international climate models surveyed by the Bureau indicate the possibility of ocean conditions nearing or exceeding El Niño thresholds by early summer, with the remainder favouring persistence of neutral conditions. For those models which indicate suprassing El Niño thresholds, the forecast peak central equatorial Pacific SSTs generally only exceed threshold levels by small margins, suggesting any event is likely to be relatively weak.
- Indian Ocean Dipole
The Indian Ocean Dipole (IOD) index has risen over the past two weeks. The latest weekly index value to 21 September is 0.0 °C; well within the neutral range.
Waters in parts of the eastern Indian Ocean remain warmer than average although anomalies in this region have been declining over recent weeks and waters to the northwest of Australia are now near average temperatures for this time of year. It is likely that the 2014 negative IOD event had ended. All climate models surveyed in the model outlooks favour a continuation of neutral IOD values over coming months.