By Fanja Saholiarisoa ANTANANARIVO, Feb 19 (Reuters) - Nearly 25,000 people are in need of humanitarian aid after a series of floods in Madagascar, while another tropical storm threatens the island's southwest region, a government official said on Monday. Rising flood waters have covered houses, cut off main roads, and destroyed an estimated 200,000 tonnes of rice on the world's fourth-largest island. "The number of victims has risen to exactly 24,780 people ... but this number will rise because some affected regions have not yet been able to send their figures," said Jacky Rolland Randimbiarison, executive secretary of the island's emergency management agency. So far this cyclone season -- which usually lasts between November and March -- six cyclones have hit Madadgascar, the worst of which were Bondo and Clovis in January, Randimbiarison said. He said another tropical storm, Favio, was threatening southwestern Madagascar.