La Niña weather, with possible floods and droughts, likely to last for months – UN

La Niña weather, with possible floods and droughts, likely to last for months – UN

The La Niña weather pattern is likely to continue and may strengthen over the next four to six months, potentially bringing abnormal conditions to widely separate areas of the world, from floods to droughts to below or above normal temperatures, the United Nations weather agency reported today.
La Niña, characterized by unusually cool ocean temperatures in the central and eastern tropical Pacific, is the opposite of El Niño, characterized by unusually warm ocean temperatures, and both events can last for 12 months or more, disrupting normal tropical rainfall atmospheric circulation, with widespread impacts on climate in many parts of the world.

But although the current La Niña has similarities to past events, its local impacts may differ from those observed in the past, the World Meteorological Organization (WMO) warned in its latest update, stressing that for managing climate-related risks, it is important to consider both prevailing La Niña conditions and other factors with potential influence on the local climate.

Generally with La Niña, rainfall increases across the western equatorial Pacific, Indonesia and the Philippines and is nearly absent across the eastern equatorial Pacific. Wetter-than-normal conditions tend to prevail during December-February over northern South America and southern Africa, and during June-August over south-eastern Australia.

Drier-than-normal conditions are generally observed along coastal Ecuador, north-western Peru and equatorial eastern Africa during December-February, and over southern Brazil and central Argentina during June-August.

La Niña also contributes to large-scale temperature anomalies worldwide, with most affected regions experiencing abnormally cool conditions. Below-normal temperatures occur during December-February in south-eastern Africa, Japan, southern Alaska, west and central Canada, and south-eastern Brazil, and during June-August in India, south-eastern Asia, the west coast of South America, the Gulf of Guinea, northern South America and portions of Central America.

Warmer-than-normal conditions occur during December-February along the Gulf coast of the United States.

“Almost all forecast models predict continuation and possible further strengthening of this La Niña episode for the next 4 to 6 months, taking the event well into the first quarter of 2011,” WMO said.

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.