El Nino weather system appears for 1st time since 2010

El Nino, a temperature anomaly in the Pacific Ocean that can cause unusual weather patterns around the world, is back.

Australia's Bureau of Meteorology announced today that El Nino thresholds have been reached in the tropical Pacific from the first time since March 2010.

El Nino is the name given to unusually warm temperatures in the equatorial Pacific that can cause changes to wind, rainfall and temperature patterns in other parts of the globe. For example, in Canada, an El Nino that lasts through the winter months generally leads to warmerwinters from British Columbiato central Quebec and drier conditions inland.

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Australia's Bureau of Meteorology isn't the only organization confirming the arrival of El Nino the U.S. National Oceanic and Atmospheric Administration had announced El Nino's arrival back in March, but said it was weak and unlikely to have major effects on weather patterns. An update in April said El Nino had strengthened slightlyover the course of March.

As of early May, "it's getting close to what we would term moderate," saidMike Halpert, deputy director for NOAA's climate prediction centre, in an interview with CBC News. He added thatthe two organizations have slightly differentthresholds for El NinoAustralia's is 0.3 degrees higher.

El Nino typically leads to heavy rainfall on the U.S. Gulf Coast and western North America. But NOAAsaid this year's El Nino is likely too late and too weak to ease the drought in California.

NOAA predicted a 70 per cent chance that El Nino conditions would last through summer and a 60 per cent chance they'd continue through fall. It is set to give another update Thursday.

Greatest effect in winter

The Australia Bureau of Meteorology predicts this El Ninowill strengthen during winter.

However, as of the beginning of April, NOAA research scientist Emily Becker said in a blog post thatit was way too early to know if this El Nino will be strong "or even if El Nino will continue into this coming winter the time of year when [it] exerts its greatest influence on global precipitation and temperature patterns."

Based on climate models, meteorologists had been expecting an El Nino for much of last year, but it never arrived.

According to Environment Canada,El Ninoeventsgenerally appear every two to seven years andlast 12 to 18 months, although one El Nino in the early 1990s lasted four years. The last El Nino in 2009-10 was a strong one, while the previous one, in 2006-07, was weak to moderate, NOAA says.

Some of the weather patterns linked to El Nino include heavy rainfall in the central Pacific and western North America and reduced rainfall over Indonesia.