La Niña shows some weakening
Issued on Tuesday 14 February | Product Code IDCKGEWWOO
The La Niña showed some signs of weakening over the past fortnight as the tropical Pacific Ocean warmed. However, La Niña remains in place and is likely to influence Australian climate over the coming months. Climate models surveyed by the Bureau show a continued decline of La Niña, with a neutral ENSO state expected in the southern hemisphere autumn.
Over the past fortnight, sea surface temperatures have warmed across the tropical Pacific, most significantly over the central to eastern Pacific regions, associated with a brief easing of the trade winds. Other indicators of La Niña, such as the Southern Oscillation Index (SOI), and cloudiness over the equatorial Pacific Ocean have generally remained steady at La Niña levels.
La Niña periods are usually, but not always, associated with above normal rainfall and below normal daytime temperatures from winter through summer across eastern and northern Australia. Tropical cyclone risk is increased for northern Australia during the cyclone season (November to April), peaking in February and March. For detailed rainfall, temperature and tropical cyclone outlooks, please see: www.bom.gov.au/climate/ahead.
Please Note: The ENSO Wrap Up will now be issued on Tuesdays.
Next update expected by 28 February 2012 | print version
Further Details
Sea Surface Temperatures
Sea Surface Temperatures
- Monthly sea surface temperatures:
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Sea surface temperature (SST) anomalies continued to cool in the central equatorial Pacific Ocean during January, but warmed in the eastern Pacific. The sea surface temperature (SST) anomaly map for January shows cool anomalies in the central Pacific near to and just east of the dateline more than 1 °C cooler than normal.
Index December January Temperature change NINO3 −0.6 −0.4 0.2 °C warmer NINO3.4 −0.8 −0.9 0.1 °C cooler NINO4 −0.8 −1.0 0.2 °C cooler 
- Weekly sea surface temperatures:
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During the past two weeks, sea surface temperature anomalies in the central equatorial Pacific have warmed; all three NINO indices monitored also show warming during this period. The SST anomaly map for the week ending 12 February shows cool anomalies remain across most of the central equatorial Pacific, with areas more than 1 °C cooler than normal for this time of the year.
Index Previous Current Temperature change
(2 weeks)NINO3 −0.5 −0.2 0.3 °C warmer NINO3.4 −1.0 −0.7 0.3 °C warmer NINO4 −1.0 −0.8 0.2 °C warmer 
Pacific ocean sub-surface temperatures
Sub-surface Pacific Ocean temperatures
- Monthly sub-surface:
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The four-month sequence of sub-surface Pacific Ocean equatorial temperature anomalies shows that the cool anomalies in the sub-surface of the central and eastern Pacific continued to expand during January. A large volume of water in the sub-surface of the Pacific between about 160°W and 100°W is more than 4 °C cooler than average. West of the dateline, warm anomalies have strengthened, with the warmest water here now reaching more than 4 °C warmer than average for January. 
- Weekly sub-surface:
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The volume of cooler than average water in the sub-surface of the eastern tropical Pacific has continued to show weakening over the past two weeks. The map for the 5 days ending 12 February shows a small volume of water more than 4 °C cooler than usual for this time of the year remains in the sub-surface. The surface of the far eastern tropical Pacific shows shallow warm anomalies have developed over the past two weeks. 
Animation of recent sub-surface changes | Archive of sub-surface temperature charts
- Southern Oscillation Index:
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During the past fortnight, the Southern Oscillation Index (SOI) dropped to near La Niña threshold levels before increasing again. The latest (12 February) 30-day SOI value is +11.9.
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:
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Trade winds have continued to strengthen slightly over the past two weeks in the western tropical Pacific. The latest wind anomaly map, for the 5 days ending 12 February, shows trade winds continue to be stronger than average across most of the equatorial Pacific, although westerly winds have emerged in the eastern Pacific.
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 dateline:
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Cloudiness near the dateline has remained suppressed over the past two weeks.
The majority of outlooks from leading international climate models surveyed by the Bureau indicate that the current La Niña will decline over the coming weeks. The current event is expected to persist through the remainder of summer, but neutral values are forecast for the coming autumn.
- Climate Models:
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The majority of outlooks from leading international climate models surveyed by the Bureau indicate that the current La Niña will decline over the coming weeks. The current event is expected to persist through the remainder of summer, but neutral values are forecast for the coming autumn.
- Indian Ocean Dipole:
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The Indian Ocean Dipole (IOD) typically has little influence in Australia over summer. The IOD index is currently neutral; the index value for the week ending 12 February was −0.4.
Recent forecasts from the POAMA model predict neutral IOD conditions for autumn.
Archive
Related links
- About the 2010−11 La Niña
- About ENSO
- El Niño
- La Niña
- IOD
- World Meteorological Organization El Niño/La Niña Update
- Tropical (MJO) Monitoring
Impact on Rainfall
Climate links
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