Factbox: U.S. weather forecaster's El Nino/La Nina watch

Reuters

(Reuters) - The U.S. weather forecaster said on Thursday the chances of El Nino striking during the Northern Hemisphere summer exceed 65 percent, three months after issuing its first alert that the weather pattern could return this year.

The latest outlook is broadly inline with Australia's Bureau of Meteorology (BOM), which said this week the weather pattern is likely to emerge as early as July. It pegged the likelihood at 70 percent.

The anomaly heats up tropical oceans in East Asia, sending warm air into the United States and South America, often causing flooding and heavy rains. It can also trigger drought conditions in Southeast Asia and Australia, regions that produce some of the world's major food staples, such as sugar cane and grains.

Here are some details about recent weather alerts by the Climate Prediction Center (CPC), an agency of the U.S. National Weather Service.

May: Conditions will remain neutral for the Northern Hemisphere spring, but the chances of El Nino striking increase during the remainder of the year, exceeding 65 percent during the summer.

((Click here for CPC's latest outlook: http://link.reuters.com/tuv97k))

March: CPC issued its first El Nino watch since October 2012, warning the phenomenon that can wreak havoc on weather and roil global crops could strike as early as the Northern Hemisphere summer.

The CPC issues an alert when there is a chance of El Nino or La Nina conditions developing in the coming six months.

The previous El Nino alert lasted five months from June until October 2012, but the anomaly did not materialize. The CPC dropped the alert in November 2012.

The last time the global weather system was roiled by extreme weather anomalies was in 2011 by El Nino's infamous counterpart La Nina.

In 2011, La Nina conditions, an abnormal cooling of waters in the equatorial Pacific, caused extreme weather conditions in Asia and the Americas.

The phenomenon was also blamed for the worst drought in a century in Texas, the country's biggest cotton growing state, and severe dry spells in South America that killed crops.

The CPC dropped its La Nina watch in May 2012.

(Reporting by Josephine Mason; Editing by Marguerita Choy)

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