UPDATE 1-Another big storm, growing stronger, set to hit central Mozambique

(Adds details, OCHA quote)

JOHANNESBURG, Jan 22 (Reuters) - A powerful storm nearing Mozambique is expected to intensify into a tropical cyclone on Friday, according to forecasts, dumping rain onto already swollen rivers in an area devastated by Cyclone Idai less than two years ago.

Tropical Storm Eloise, currently over the Mozambique channel whose warm Indian Ocean waters fuel its strength, could develop into a category 3 tropical cyclone, Mozambique's National Meteorological Institute (INAM) said.

Cyclones and flash floods, which used to batter this stretch of southeast African coastline only rarely, have become a regular occurrence as warmer waters linked to global warming from greenhouse gas emissions cause stronger storms while rising seas make low-lying coastlines vulnerable to them, experts say.

INAM said Eloise, due to make landfall on Saturday, could pack winds of up to 140 kmh (87 mph) and deliver 200 millimetres (7.87 inches) of rain in 24 hours. This has raised fears of widespread flooding like that which killed over 1,000 people across Mozambique, Malawi and Zimbabwe, displaced many more and wiped out crops when Idai struck in March 2019.

Mozambique, one of the world's poorest countries, was hit by another cyclone, dubbed Kenneth, six weeks later, bringing floods and high winds that flattened several villages.

Eloise is expected to pummel the port city of Beira and surrounding areas - which bore the brunt of Idai. Some areas are already flooded after heavy rains.

"There are growing concerns regarding the potential for widespread floods," the U.N. Office for the Coordination of Humanitarian Affairs (OCHA) said, adding rivers in the region were already on alert due to high water levels.

The International Organisation of Migration says there are 93,418 displaced people in four provinces in Mozambique's central region, most forced from their homes by Cyclone Idai and others displaced by more recent storms and floods.

Idai spawned a vast humanitarian machinery that may mean better preparedness this time around, but resources are already stretched, including by an escalating Islamist insurgency in Mozambique's north.

The International Organisation of Migration said this week that just under 1,000 people had been relocated within Beira or surrounding areas due to flooding. The government is warning people to prepare via phone messages, radio and loudspeakers. Last time it was criticised for not doing enough to prepare.

After hitting land, Eloise is forecast to lose strength as it travels inland to southern Zimbabwe, eastern South Africa and far eastern Botswana, but carry heavy rains with it. (Reporting by Emma Rumney; Editing by Tim Cocks and Mark Heinrich)