The World Meteorological Organization says floods in Libya were caused by extreme rainfall from a storm system called a medicane, or Mediterranean hurricane.
The WMO says the storm, named Daniel, developed in Greece in early September. It brought a record 750 millimeters of rain -- or about 18 months of precipitation -- in 24 hours to central Greece last week.
Greece's state-run news agency is reporting that at least 15 people died.
The storm grew stronger before making landfall in Libya.
Suzanne Gray, a professor of meteorology at the University of Reading in Britain, says that although medicanes occur only once to three times per year, they can be devastating upon making landfall due to flooding, storm surges and strong winds.