Weak La Nina Possible In 2011, No Chance Of El Nino: WMO

Stephanie Nebehay PlanetArk 2 Sep 11;

La Nina, a weather phenomenon typically linked to flooding in the Asia-Pacific, African drought and a more intense hurricane season over the Atlantic, could occur in a weak form this year, the World Meteorological Organization said Thursday.

A borderline La Nina situation has developed in recent weeks in the tropical part of the Pacific Ocean, where sea surface temperatures have cooled slightly, but there is an equal chance of neutral conditions returning, the United Nations agency said.

"If a La Nina event does occur, current indications are that it would be considerably weaker than the moderate to strong 2010-2011 episode, which ended in May 2011," the WMO said in a statement calling for continued close monitoring.

But there is virtually no prospect of El Nino, its opposite weather phenomenon which warms the Pacific, occurring this year, it said in an assessment based on data from climate prediction centers and experts worldwide.

La Nina, a natural cooling of the Pacific Ocean, occurs every 2 to 7 years, causing major climate fluctuations including altered tropical rainfall patterns, according to WMO expert Rupa Kumar Kolli.

The 2010-2011 La Nina episode was linked to disastrous flooding in parts of Australia, Indonesia, Southeast Asia, and parts of South America including Colombia, the WMO said.

It also contributed to drought in parts of the Horn of Africa, southeastern South America and the southern United States, and weaker winter monsoons in Sri Lanka and southern India.


"The last La Nina situation, which was moderate to strong in intensity, was believed to have caused the drought conditions over the greater Horn of Africa which we all know is undergoing a famine type of situation," Kolli said, referring to parts of Somalia which have been declared famine zones.

"So for them this can be considered to be cause for additional alert," he said.

But the climate over eastern Africa is strongly influenced by the Indian Ocean, which can create opposite effects, so both factors must be taken into account, he added. Experts were now meeting in Entebbe, Uganda to chart a regional outlook.

La Nina weather could return to delay planting of Brazil's grain crop again, forcing Chinese buyers to rely on U.S. Gulf port soybeans longer and putting Brazil's corn output at risk, grain specialists said Tuesday.

Brazil's coffee belt may face more weather risks if rainfall is erratic in the world's top coffee-growing country, as some forecasters fear, during the critical flowering phase that will define next year's crop.

La Nina is also closely associated with a more intense hurricane season over the tropical North Atlantic, Kolli said.

"At this stage either a normal (hurricane) season or a slightly more intense season, that's what we can expect based on a neutral to La Nina type of outlook available to us today."

A low-pressure system pushing northwest through the Gulf of Mexico has a strong chance of becoming a tropical cyclone in the next two days and threatening southern U.S. states, the National Hurricane Center said Thursday.

The warning came after Irene battered the eastern U.S. coast with up to 15 inches of rain at the weekend.

(Editing by Mark Heinrich)

La Nina risks increase, to detriment of E. Africa: UNAFP Yahoo News 2 Sep 11;

There is a 50 percent chance the climatic condition known as La Nina -- which is associated with droughts in East Africa -- will return this year, the UN weather agency said Thursday.

"We are increasing the probability of La Nina from 25 to 50 percent," Rupa Kumar Kolli, a climate expert at the World Meteorological Organization said, explaining that the rise was due to recent temperature observations in the Pacific.

"La Nina is associated with drought conditions in east Africa. The last La Nina situation was believed to have caused the drought condition in the greater Horn of Africa," he told reporters, referring to the La Nina event which ended in May.

He however stressed that meteorological predictions were difficult to make and depended on a variety of local conditions.

"And even if a La Nina situation reemerges, it is very likely it will be a very weak La Nina event," Kolli explained.

Over 12 million people across the Horn of Africa are reeling from the region's worst drought in decades, which led UN in July to declare the first famine this century.

According to a WMO press statement, La Nina is characterised by "unusually cool ocean surface temperatures in ... the central and eastern tropical Pacific."

The weather pattern was blamed for extremely heavy downpours in Australia, southeast Asia and sSouth America over late 2010 and early 2011, the WMO said in May.

Although the ocean temperatures in the Pacific leveled to their long-term, or "neutral" conditions that month, "observations during recent weeks indicate a drift toward the cool side ... in terms of surface as well as subsurface ocean temperatures," WMO said today.

"If this cooling persists ... for another few weeks then we will be going into another la Nina situation," Kolli said.

"For (the Horn of Africa), this can be understood as a cause for additional alert," Kolli added.