The World Meteorological Organisation warned in July that the combination of tropical wind patterns over the Pacific Ocean and cooler than normal sea temperatures off western Latin America could have a "planetary" impact.

WMO climatologist Omar Baddour told journalists that the link between "La Nina" and flooding in western Africa had been closely studied since the 1990s.

"We have found a very close relationship between La Nina and the phenomenon of flooding in West Africa," Baddour told journalists.

"It was therefore very probable that a rather rainy season would occur in the region extending from Sudan in the east to Senegal in the west," he added.

At least 1.5 million people have been affected and 270 have died in some of Africa's worst flooding in decades, which has struck 18 countries.

West African nations including Ghana and Nigeria are amongst the worst affected, along with Sudan and Uganda on the other side of the continent.

The WMO said the greater probability of wet weather in West Africa at the end of summer had been highlighted in a long term forecast given at a regional forum of African weather experts in May.

"The season started a little later compared to the average, but the months of August and September especially have been very very rainy in West Africa," Baddour underlined.

The WMO on Thursday called for a sharp boost in investment in weather forecasting, especially in developing nations, to help them deal with the impact of climate change and greater incidence of extreme weather conditions.

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