Nearly 9 inches (23 centimeters) of rain fell on the mountainous country late Wednesday, followed by another 6 inches (15 centimeters) early Thursday, according to the Antigua Weather Service.
"The situation is grim. It is dangerous," said Ian Pinard, Dominica's communications minister.
Two people were reported missing in the capital, and another three in the island's southeastern region, said national disaster official Don Corriette.
