WMO Says Moderate to Strong La Niña Expected to Continue into 2011
Geneva, 11 October 2010 (WMO) - Moderate to strong La Niña conditions are now well-established in the equatorial Pacific Ocean, and are likely to continue at least until the first quarter of next year, according to the El Niño/La Niña Update issued today by the World Meteorological Organization. La Niña conditions may possibly further strengthen during the next four to six months.
La Niña is characterized by unusually cool ocean temperatures in the central and eastern tropical Pacific. It is the opposite of El Niño, which is characterized by unusually warm ocean temperatures. Both events can last for 12 months or more and disrupt the normal patterns of tropical precipitation and atmospheric circulation, and have widespread impacts on climate in many parts of the world accompanied by the associated climate-related risks.
“Almost all forecast models predict continuation and possible further strengthening of this La Niña episode for the next 4-6 months, taking the event well into the first quarter of 2011,” says the WMO Update.
This is because of the strong interaction between the oceanic and atmospheric aspects of the current event and the large area of below-average subsurface temperatures.
The current La Niña developed quickly in June and July 2010, following the dissipation of the 2009/2010 El Niño in April. Since August, the event has been moderate to strong.
In the central and eastern equatorial Pacific, sea surface temperatures are around 1.5 degrees Celsius cooler than average. The atmosphere across the tropical Pacific is now well coupled to this sea surface temperature pattern, with strengthened trade winds and reduced cloudiness over a substantial part of the central and eastern equatorial Pacific.
The subsurface waters of the central and eastern equatorial Pacific also strongly reflect La Niña conditions, with temperatures being 2 to 6 degrees Celsius below average. This large volume of anomalously cold water will likely maintain or strengthen the cold waters already at the ocean surface.
Climate Risk Management
Although the current La Niña has some similarities to past events, its impact upon local climates may differ from those observed in the past. For management of climate-related risks, it is therefore important to consult regional climate information and seasonal outlooks that consider both the prevailing La Niña conditions and other factors with potential influence on the local climate.
National and regional meteorological institutions and regional Climate Outlook Forums around the world have been issuing detailed, regionally tailored climate outlooks to help governments, businesses and civil society prepare for - and thus reduce - climate risks such as flooding and drought situations generally associated with La Niña.
The El Niño/La Niña Update is a consensus-based product prepared by WMO in close collaboration with the International Research Institute for Climate and Society (IRI), USA, based on input from climate prediction centres and experts around the world. It is a contribution to the United Nations Inter-Agency Task Force on Natural Disaster Reduction.
Workshop on El Niño/Southern Oscillation in South America
El Niño and La Niña represent opposite extremes in the El Niño/Southern Oscillation Cycle, or the ENSO Cycle. The ENSO cycle is a natural large-scale climatic phenomenon and refers to the coherent and sometimes strong year-to-year variations in sea- surface temperatures, rainfall patterns, surface air pressure, and atmospheric circulation that occur across the equatorial Pacific Ocean and is the subject of intense research in many countries due to the associated climatic impacts around the world.
To further this research, with a specific focus on South America, the World Climate Research Programme is sponsoring an International Workshop on ENSO, Decadal Variability and Climate Change in South America, being organized in collaboration with the International Centre for Research on El Niño (Centro Internacional para la Investigación del Fenómeno El Niño, CIIFEN) during 12-14 October in Guayaquil, Ecuador.
Climate experts around the world will discuss subjects including naturally occurring decadal variability in ENSO impacts, differences in the details of sea-surface temperature patterns between El Niño events, and the influence of global warming on ENSO and on the way ENSO affects global weather patterns. This research will lead to more useful information for decision-making in the wider community.
Notes to Editors:
Generally, during La Niña episodes rainfall is increased across the western equatorial Pacific, Indonesia and the Philippines and is nearly absent across the eastern equatorial Pacific. Wetter than normal conditions tend to be observed during December-February over northern South America and southern Africa, and during June-August over southeastern Australia. Drier than normal conditions are generally observed along coastal Ecuador, northwestern Peru and equatorial eastern Africa during December to February, and over southern Brazil and central Argentina during June-August.
La Niña episodes also contribute to large-scale temperature departures throughout the world, with most of the affected regions experiencing abnormally cool conditions. These include: below-normal temperatures during December-February over southeastern Africa, Japan, southern Alaska and western/central Canada, and southeastern Brazil; cooler than normal conditions during June-August across India and southeastern Asia, along the west coast of South America, across the Gulf of Guinea region, and across northern South America and portions of central America; and warmer than normal conditions during December-February along the Gulf coast of the United States.
El Niño/La Niña events change the likelihood of particular climate patterns around the globe, but the outcomes of each event are never exactly the same. Further, it is important to recognize that while the state of El Niño or La Niña may be the most important factor leading to climate risk assessments in many regions, climate extremes may also develop as a consequence of ocean/atmosphere interactions outside of the tropical Pacific. Therefore, climate outlooks should adequately incorporate the effects of both the current La Niña and other climate factors of importance to specific locations.
More detailed interpretations of regional climate fluctuations will be generated over the coming months and will be made available through National Meteorological and Hydrological Services. For web links, please visit http:
For details on the International Workshop on ENSO, Decadal Variability and Climate Change in South America, visit www.clivar.org/meetings/enso_2010.php
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