ENSO Wrap-Up
Current state of the Pacific and Indian Ocean
Near El Niño conditions persist in tropical Pacific Ocean
Issued on 23 December 2014 | Product Code IDCKGEWW00
The tropical Pacific Ocean continues to border on El Niño thresholds, with rainfall patterns around the Pacific Ocean basin, and at times further afield, displaying El Niño-like patterns over recent months.
Indicators remain broadly consistent with borderline El Niño conditions. Sea surface temperatures have exceeded thresholds for a number of weeks, and the Southern Oscillation Index (SOI) has generally been negative for the past few months. Trade winds have been near-average along the equator, but weaker in the broader tropical belt. Together, these indicate some weak coupling of the atmosphere and ocean may be occuring.
Climate models expect little change over the next two to three months, with most predicting a persistence of the current warm sea surface temperatures. If current conditions do persist or strengthen into next year, 2014–15 is likely to be considered a weak El Niño. As a result, the Bureau's ENSO Tracker status remains at ALERT.
Regardless of El Niño status, El Niño-like impacts are likely to continue, as shown by recent seasonal outlooks. For Australia, this means drier and warmer than average weather is likely in many areas.
Next update expected on 6 January 2014 | print version
- Weekly sea surface temperatures
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The pattern of sea surface temperature (SST) anomalies in the equatorial Pacific remains generally similar to two weeks ago, with warm anomalies along the entire equator (see SST anomaly map for the week ending 21 December). Warm anomalies have decreased slightly in magnitude across the broader western tropical Pacific, particularly west of the Date Line. Warm anomalies are also present across most of the Indian Ocean, large parts of the northern Pacific Basin and waters around the coastline of Australia. Warm anomalies have increased in waters around northern Australia over the past week.
In the central equatorial Pacific, the NINO 3.4 region has remained above the +0.8 °C threshold value for El Niño for the past 7 weeks. An anomaly greater than +0.8 °C for a sustained period typically indicates El Niño.
Baseline period 1961–1990. Index Previous Current Temperature change
(1 week)NINO3 +0.9 +0.9 no change NINO3.4 +0.9 +0.9 no change NINO4 +1.1 +1.1 no change - Monthly sea surface temperatures
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The SST anomaly map for November shows warmer than average waters across the entire equatorial Pacific as well as across much of the northern Pacific Basin, around southern and northwestern Australia and across much of the Indian Ocean. This pattern was generally similar to the previous month, although SSTs along the equator have warmed again during November.
Baseline period 1961–1990. Index October November Temperature change NINO3 +0.7 +0.9 0.2 °C warmer NINO3.4 +0.6 +0.9 0.3 °C warmer NINO4 +0.8 +1.0 0.2 °C warmer
- 5-day sub-surface temperatures
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The sub-surface temperature map for the 5 days ending 21 December shows temperatures are warmer than average below the surface of the eastern equatorial Pacific. Sub-surface waters are more than 3 °C warmer than average in an area east of 120°W at around 100 m to 50 m depth. This pool of warmer-than-average water has continued to move slowly eastward and rise closer to the surface over the past week.
- Monthly sub-surface temperatures
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The four-month sequence of sub-surface temperature anomalies (to 22 December) shows warm anomalies are present across most of top 100 m of the equatorial sub-surface profile for December. There are small areas of weak cool anomalies present at around 150 m depth in the western and central equatorial Pacific. Warm anomalies near to the surface have expanded eastward during December, when compared to November.
- Southern Oscillation Index
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The Southern Oscillation Index (SOI) has dropped slightly over the past week. The latest 30-day SOI value to 21 December is −6.1.
Sustained positive values of the SOI above +8 may indicate La Niña, while sustained negative values below −8 may indicate El Niño. Values of between about +8 and −8 generally indicate neutral conditions.
- Trade winds
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Trade winds were near-average over the majority of the tropical Pacific for the 5 days ending 21 December, but slightly stronger than average in the far western equatorial Pacific (see map).
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.
- Data Source:
- TAO/TRITON data
- Time-longitude wind anomalies
- Cloudiness near the Date Line
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Cloudiness near the Date Line has generally been near average over the past week.
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
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Four of the eight surveyed international climate models predict that central Pacific Ocean SSTs will reach El Niño thresholds before autumn. Around half of the models predict SSTs will be above the threshold value during some or all of the austral autumn, while the others indicate warm but neutral conditions. On the whole, these outlooks continue to indicate that peak central equatorial Pacific SSTs are unlikely to rise far beyond the threshold value.
- Indian Ocean Dipole
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The Indian Ocean Dipole (IOD) index remains neutral. The latest weekly index value to 21 December is −0.4 °C. Climate models surveyed in the model outlooks favour a continuation of neutral IOD values for the remainder of the southern hemisphere summer.
The IOD typically has little influence on the Australian climate from December to April.
