A million Africans already suffering from severe flooding have been warned of further misery to come with heavy rain predicted from West to East.
Some African countries have endured months of flooding
The United Nations says 250 people have died and more than 600,000 people been made homeless across 17 countries.
The World Food Programme has urged governments to do all they can to help provide immediate relief.
WFP has launched an $60m appeal for food aid to Uganda alone, where it estimates 1.7 m people will go hungry.
North-eastern Uganda has lost most of its crops to flooding, after the heaviest rains in three decades.
"We anticipate that the situation will worsen," said Elizabeth Byrs from the UN Office of the Coordination of Humanitarian Affairs (OCHA), with a flood zone already stretching "from the Atlantic coast to the Red Sea."
In Ethiopia, more than 4,000 people are stranded in the eastern Afar region after a dam collapsed.
The UN relief co-ordinator in the Sudanese capital, Khartoum, John Clarke, told the BBC more than 250,000 had been left homeless in that country alone.
Countries in East Africa regularly flood at this time of year, but West African nations are much less able to deal with the deluge, the World Food Programme says.
In northern Ghana, more than 30 people have died and flooding has ruined the supply of clean water.
The Ghanaian Navy, local and international agencies are coordinating their emergency response.
Deaths directly attributed to the floods include:
- 32 in Ghana
- 41 in Nigeria
- 33 in Burkina Faso
- 20 in Togo
- 12 in Niger
- 4 in Somalia
- 4 in Morocco
- 2 in Mauritania
- 64 in Sudan
- 21 in Uganda
- 18 in Rwanda
- 12 in Kenya
- 17 in Ethiopia.