US government scientists say the periodic climate phenomenon known as El Nino has developed in the Pacific Ocean, threatening extreme weather in many parts of the world.
The scientists say this El Nino is likely to strengthen towards the end of the year and into early 2007.
The phenomenon begins with a warming of waters in the eastern Pacific and scientists say there has been a steep rise in water temperature over the past two weeks.
The scientists say this may explain why this year's Atlantic hurricane season has so far been weaker than expected as winds associated with El Nino often disrupt and weaken storm function.
They are also predicting a milder than average winter in north America and wetter weather for the US Gulf Coast and Florida.
