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Weak La Niña may cause wet weather in parts of the world

Parts of the world may experience increased rainfall over the next few months due to the likelihood of weak La Niña conditions, according to a forecast from the World Meteorological Organization (WMO). It would mark the second La Niña in as many years.

La Niña, which is also referred to as a "cold event," is characterized by unusually cool ocean temperatures in the central and eastern equatorial Pacific along with changes in the tropical atmospheric circulation. It is the opposite of El Niño, which is characterized by unusually warm ocean temperatures.

An update from the World Meteorological Organization said sea surface temperatures in the eastern tropical Pacific are approaching La Niña levels since cooling started in August. Atmospheric patterns, however, are currently not showing features that are typically associated with La Niña events.

As a result, the organization estimates with a 50 to 55 percent probability that La Niña conditions will develop in the final quarter of this year. If it does occur, it will likely remain weak and conditions would return to normal in the first quarter of 2018.

"Large-scale climate events like La Niña extend their influence over countries which are home to many millions of people," said WMO Secretary-General Petteri Taalas. "Our ability to predict these events in advance is vitally important to help planning in sensitive sectors like farming, water management, public health, energy and transport and provide early warnings of the associated risks."

La Niña episodes feature a wave-like jet stream flow over the United States and Canada during winter, with colder and stormier than average conditions across the North and warmer and less stormy conditions across the South.

And while every La Niña is unique, it is often associated with wet conditions in eastern Australia, Indonesia, the Philippines, Thailand and South Asia. It usually leads to increased rainfall in northeast Brazil, Colombia, and other northern parts of South America, and drier than normal conditions in Uruguay, parts of Argentina, coastal Ecuador and northwestern Peru.

La Niña events are generally also associated with increased rainfall in southern Africa, and rainfall deficiency in equatorial eastern Africa - for instance eastern Kenya and Somalia, as well as deficient northeast monsoon rainfall in the southernmost parts of South Asia.

La Niña tends to suppress tropical cyclone activity in the central and eastern Pacific basins, and enhances it across the Atlantic basin.

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