Geneva, 25 September 2012 (WMO) – A weak El Niño may develop in September and October and last until the northern hemisphere winter, according to the World Meteorological Organization's new El Niño/La Niña Update.
The El Niño phenomenon is due to large-scale interactions between the ocean and the atmosphere. It is characterized by unusually warm ocean surface temperatures in the central and eastern tropical Pacific, in contrast to the unusually cool ocean surface temperatures witnessed in the same region during La Niña events. Both El Niño and La Niña have a large influence on weather and climate around the globe.
"Our ability to predict the climate a season in advance has improved dramatically thanks to increased scientific understanding about El Niño/La Niña events," said WMO Secretary-General Michel Jarraud. "Provision of El Niño/La Niña Updates in support of climate services has become an important tool for the disaster risk reduction, water management, agricultural and health sectors," he said.
WMO is spearheading international efforts to improve climate services, including through the provision of seasonal predictions and regional climate outlooks, to help countries cope with climate variability and adapt to climate change. An extraordinary session of the World Meteorological Congress at the end of October will decide on the implementation plan for a Global Framework for Climate Services.
The WMO El Niño/La Niña Update is a consensus product based on inputs from climate prediction centres and experts around the globe. It is recognized as an authoritative source of information on a phenomenon which potentially has a major impact on lives and livelihoods in many parts of the world.
During July and August 2012, the tropical Pacific sea surface temperature increased and exceeded weak El Niño thresholds, according to the Update. But atmospheric characteristics of El Niño – sea level pressure, trade winds and cloudiness – have not yet developed. An atmospheric response is necessary for an El Niño to have global impacts. The ocean-atmosphere system as a whole therefore is considered to be currently in a neutral state (neither El Niño nor La Niña) but is "more likely than not" to respond in due course in a manner consistent with an El Niño.
The majority of climate forecast models say there is a "moderately high likelihood" that El Niño conditions will develop during September and October and last into the northern hemisphere winter 2012-2013. If an El Niño event does develop, it is most likely to be weak, according to WMO's Update. That said, continuation of neutral conditions could not be ruled out.
It is important to note that El Niño and La Niña are not the only factors that drive global climate patterns. Conditions in the tropical Indian and Atlantic oceans, for instance, also have an important influence on surrounding continental climate patterns.
More detailed interpretations of regional climate fluctuations will be generated by the climate forecasting community over the coming months and will be made available through the National Meteorological and Hydrological Services.
El Niño was originally recognized by fishermen off the coast of South America as the appearance of unusually warm water in the Pacific ocean around Christmas time. El Niño means the "Little Boy" or "Christ child" in Spanish. It is the opposite of La Niña or "Little Girl."
No two El Niño/La Niña events are the same and they also vary depending on the time of the year during which the conditions evolve. In some parts of the world, other climate phenomenon (such as the North Atlantic Oscillation) also play a critical in influencing the climate.
WMO's Updates do not address the specific impacts of El Niño/La Niña events, and the National Meteorological and Hydrological Services have the operational responsibility to use the available information on El Niño/La Niña and other factors to determine country-specific climate impacts. (See http://www.wmo.int/pages/members/members_en.html for list of members)
Past El Niño events during the northern hemisphere autumn and winter have been associated, among others, with drier than normal conditions in parts of Australia, Indonesia, the Philippines, northeastern Brazil, southeastern Africa and parts of Asia.
Wetter than normal conditions have, in the past, tended to be experienced in Ecuador and northern Peru, as well as southern Brazil to central Argentina and parts of eastern Africa. El Niño winters tend to be mild over western Canada and parts of the northern United States, and wet over the southern United States.
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