GENEVA - The U.N. weather agency says there is a "moderately high likelihood" that El Nino -- the weather phenomenon that brings above normal rainfall -- will develop, but is likely to be weak if it does.

World Meteorological Organization spokeswoman Clare Nullis told reporters Tuesday that experts believe El Nino could begin in September or October and last through year-end. However, the WMO says that neutral conditions could also remain.

El Ninos are characterized by unusually warm ocean temperatures in the central and eastern equatorial Pacific, and have been associated with drought in Australia or heavy rainfall in Ecuador and Peru. The last El Nina -- its cold-water counterpart -- ended in April.

In June, WMO had noted a "slight chance" for the return of El Nino conditions by September.