The UN weather agency said on Thursday that La Nina, a phenomenon linked to flooding and drought, had re-emerged in the tropical Pacific since August but its impact is expected to be weaker this time.

"This La Nina is expected to persist through the end of this year and into early 2012, possibly strengthening to moderate intensity," said the World Meteorological Organisation in a statement.

"However, it is likely to be considerably weaker than the recent episode that was linked to flooding and drought in different parts of the world."

La Nina is characterized by unusually cool ocean surface temperatures in the central and eastern tropical Pacific.

It is the opposite of El Nino, which is marked by unusually warm ocean surface temperatures.

Both factor in the fluctuations of the world's climate.

In late 2008 La Nina was blamed for icy conditions that claimed dozens of lives across Europe.

The weather phenomenon can also bring about strong rainfall in Indonesia, Malaysia and Australia, as well as drought in South America.

The current La Nina follows closely behind the moderate to strong one that started in September 2010 and ended with neutral conditions established in May this year, the WMO said.

"Historical precedents and the latest outputs from forecast models suggest that peak intensity of this La Nina will be reached in late 2011 or early 2012, and that it is very unlikely to reach conditions as strong as those of the 2010-11 La Nina event," the statement said.