* No repetition of 1997/98 disasters seen
* Likely to last well into 2010
* Drought or heavy rains still predicted in some regions
GENEVA, Aug 19 (Reuters) - An El Nino building up in the Pacific looks like being only a mild version of the phenomenon that has in the past brought devastation around the globe, the United Nations weather agency WMO said on Wednesday.
But the World Meteorological Organisation warned that even a weak El Nino -- a phenomenon in which changing sea temperatures in the Pacific Ocean affect weather around the world -- could seriously disturb normal climate patterns in many regions, bringing drought to some places and heavy storms to others.
"What appears to be emerging is a weak to moderate El Nino, but one that will continue for the rest of this year and stretch into the first quarter of 2010," senior WMO climate scientist Rupa Kumar Kolli told a news conference.
He said the new El Nino would have nothing like the strength of the 1997-98 version -- the worst on record -- which produced extreme weather that wreaked death and destruction across the southern hemisphere and parts of the north.
That El Nino brought huge storms which battered western coasts and towns in Latin America, killing hundreds of people there and elsewhere around the globe and causing billions of dollars of damage in Asia and Australia.
Both developing countries and richer nations have been anxiously watching the new event in the Pacific, fearing that even minor changes in weather patterns could seriously damage economies already battered by the global recession.
Kolli was presenting a WMO situation report and outlook for the alternating and linked El Nino/La Nina events in which sea surface temperatures in the Pacific, the world's largest ocean, either climb above average or drop below it.
Kolli did not say how El Nino would affect any particular region.
The varying water temperatures alter atmospheric patterns and air circulation across other continents and seas, often combining with unrelated local weather developments to create wildly fluctuating extremes.
Warnings have already been issued in Australia and South Africa of potential drought and crop failure as seasonal rains fail to appear, while farmers in eastern Africa have been told to expect heavier rainfall than usual.
The WMO report said Pacific temperatures were likely to be between 0.5 and 2 degrees Celsius above the norm for the past 100 years during the new El Nino -- much lower than the 5 and in places 7 degrees above the norm of the 1997-98 event.
Australia's Bureau of Meteorology reported earlier in the day that there had been no strengthening over the past two weeks of the new El Nino -- a Latin American Spanish term meaning Christ Child. [ID:nSYB006057]
Experts say a strong event along the lines of 1997-98 would be signalling its arrival already through a sharp rise in Pacific sea temperatures from June to August.
The WMO said even a weak event, with temperatures only 0.5 degrees Celsius above normal, "can have a substantial impact on climate patterns in many parts of the world." Kolli said it could already be helping delay monsoons in India.
The WMO scientist also echoed an August 6 prediction from the U.S. government's Climate Prediction Centre that the new El Nino would reduce the number of hurricanes likely to hit the western Atlantic and Caribbean in the coming season.
(Editing by Jonathan Lynn and Tim Pearce)
Residents carry food rations from the United Nations World Food Programme (WFP) following prolonged drought at camp in Laikipia, 290 km (180 miles) east of Nairobi, August 18, 2009. The Kenyan ...
