Current state of the Pacific and Indian Ocean
Further easing of El Niño
Issued on 2 February 2016 | Product Code IDCKGEWW00
El Niño remains strong, but continues its gradual decline. Climate models suggest a return to neutral levels in the second quarter of 2016.
Close to the equator, the surface of the Pacific Ocean has now cooled by 0.5 °C since the El Niño peaked in late 2015. Below the ocean surface, cooler than average waters now extend into the central tropical Pacific Ocean. In the atmosphere, trade winds have recently returned to near-normal levels in the central and eastern Pacific, although the Southern Oscillation Index (SOI) has been strongly negative in recent weeks. During Australia's northern wet season, it is not unusual to see big fluctuations in the SOI due to the passage of tropical systems, and hence its value may not be representative of the overall ENSO state.
Based on the 26 El Niño events since 1900, around 50% have been followed by a neutral year, and 40% have been followed by La Niña. Models suggest the neutral state is the most likely for the second half of 2016, followed by La Niña, with a repeat El Niño assessed as very unlikely. Historically, the breakdown of strong El Niño events brings above average rainfall to some-but not all-parts of Australia in the first half of the year.
The Indian Ocean Dipole has little influence on Australian climate between December and April. However, Indian Ocean sea surface temperatures remain very warm across the majority of the basin which may provide extra moisture for rain systems across Australia.
Next update expected on 16 February 2016 | 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
Equatorial sea surface temperature anomalies (difference from normal) in the eastern Pacific have cooled over the past fortnight. Warm anomalies in the southeastern Pacific Ocean, off the coast of Chile, have expanded and strengthened, and the warm anomalies in the northwest have weakened. Elsewhere in the Pacific, anomalies remain mostly the same.
Surrounding Australia, anomalies off the Western Australian coast have cooled over the past fortnight. Anomalies surround most of southern and eastern Australia, with those around Tasmania greater than +3 °C in places. Warm anomalies continue to cover most of the Indian Ocean.
- Monthly sea surface temperatures
The SST anomaly map for December 2015 shows warm SST anomalies extended across nearly the entire equatorial Pacific. Warm anomalies were also present across some of the eastern half of the Pacific Basin in the northern hemisphere.
Compared to November, warm anomalies decreased slightly in some areas along the equator, and over the northeast of the Basin. Moderate to strong warm anomalies persisted across much of the Indian Ocean but showed some reduction in waters immediately adjacent to Australia.
In December, the NINO3 index in the eastern Pacific remained steady, while NINO3.4 and NINO4 showing some small decline from their event peak in November. Values in the Bureau dataset were +2.4 °C, +2.3 °C, and +1.6 °C respectively, and remain indicative of a strong El Niño event.
Baseline period 1961–1990. Index November December Temperature change NINO3 +2.4 +2.4 no change NINO3.4 +2.4 +2.3 0.1 °C cooler NINO4 +1.7 +1.6 0.1 °C cooler
- 5-day sub-surface temperatures
The sub-surface temperature map for the 5 days ending 31 January shows temperatures more than 2 °C warmer than average in the top 125 m of the ocean east of 150 ° W, tapering off to shallower depths in the central Pacific. The subsurface of the western Pacific is mostly cooler than normal reaching less than −4 ° on the Date Line, 150 m below the surface.
Both the warm anomalies in the east and the cool anomalies in the west have strengthened over the last fortnight. The focus of the cool anomalies has shifted from the western Pacific to the Date Line, and the cool anomalies extend out to 150° W, 15° further than last fortnight.
The sub-surface pattern of warm anomalies in the east and cool anomalies in the west remains consistent with El Niño. Cool anomalies are expected to migrate eastwards and cool the surface of the equatorial Pacific in the coming weeks, in line with the expected eventual return to an ENSO neutral state.
- Monthly sub-surface temperatures
The four-month sequence of sub-surface temperature anomalies (to January) shows a decrease in warm sub-surface temperature anomalies compared to December, while the area of cool sub-surface anomalies has strengthened and contracted.
During January, warm anomalies were present in the top 150 m of the equatorial Pacific sub-surface, extending between about 170°E and the South American coastline. These warm anomalies have cooled by about a degree compared to December. Cool anomalies for January covered much of the western Pacific at around 150 m depth, with a narrow area of cool anomalies underlying warm anomalies in the central region.
- Southern Oscillation Index
The 30-day Southern Oscillation Index (SOI) dipped to an event-to-date minimum of −23.6 on 26 January. The latest 30-day SOI to 31 January is −19.2.
Fluctuations of the SOI during Australia's northern wet season (October–April) are not unusual as the passage of tropical systems near Darwin and Tahiti affects atmospheric pressure. During this period, the SOI should be used cautiously; 90-day values can provide a more reliable guidance. The current 90-day SOI is −11.9.
Sustained positive values of the SOI above +7 typically indicate La Niña, while sustained negative values below −7 typically indicate El Niño. Values of between about +7 and −7 generally indicate neutral conditions.
- Trade winds
Trade winds for the 5 days ending 31 January are mostly close to normal across the equatorial Pacific Ocean. This follows a surge in westerly wind along the equator that occurred during mid-January.
Apart from the recent fortnight, 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.
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 been mixed during January with episodes of both above average and below average convection. Cloudiness near the Date Line has generally been above average since March 2015.
Cloudiness along the equator, near the Date Line, is an important indicator of ENSO, as it typically increases (negative Outgoing Long-wave Radiation (OLR) anomalies) near and to the east of the Date Line during an El Niño event and decreases (positive OLR anomalies) during a La Niña event.
- Model outlooks
All eight international climate models surveyed by the Bureau indicate central Pacific sea surface temperatures (SSTs) will continue to cool.
All but one model indicates central Pacific SSTs will fall below El Niño thresholds between April and June.
- Indian Ocean Dipole
The Indian Ocean Dipole (IOD) is neutral. The Dipole Mode Index value to 31 January was −0.51 °C.
The IOD does not typically influence Australian climate during the months December to May. When the monsoon trough is in the southern hemisphere (as it typically is between the months of December to May) neither positive nor negative IOD events are able to form.
More generally, sea surface temperatures (SSTs) remain significantly warmer than average across most of the Indian Ocean basin, with a large part of the Indian Ocean measuring warmest on record for this time of year. This unusually warm ocean is likely to increase the available moisture for weather systems travelling across Australian in the coming weeks and months, increasing the likelihood of good falls occurring across southern Australia.
See also: IOD forecasts