The Dominican Republic coast was lashed by winds
A mother and her two children, were killed in the capital, Santo Domingo, after torrential rain and crushed the wooden shack they were living in.
During Saturday, Iris was upgraded from a tropical storm to a hurricane as its winds strengthened to more than 120km/h (75mph).
Haiti, Jamaica and Cuba have issued hurricane warnings as Iris sweeps on in a north-westerly direction.
About 8cm (3in) of rain fell on Saturday in the Dominican Republic, and there were tide surges of more than 1.2 metres ( 4 to 5 ft).
The government of Haiti, which lies to the west of the Dominican Republic on the island of Hispaniola, has advised inhabitants on the south coast and in low-lying areas to move to higher ground.
Open sea
After crossing Haiti, Hurricane Iris will cross open water.
A spokesman for the National Hurricane Centre in Miami, Richard Knabb, said: "As it gets into open water, we expect it to develop more rapidly."
It could then hit Jamaica close to the capital, Kingston, and travel through the centre of the island on Sunday.
If the hurricane continues in the same direction, it could strike the tourist area in north-west Jamaica by Sunday evening.
Iris started on Thursday as a tropical depression that brought strong winds and heavy rainfall to the islands of St Vincent and St Lucia, but caused no significant damage or loss of life.
A tropical storm is classified as a hurricane if maximum winds reach 119km/h (74mph).
The hurricane season in the Caribbean occurs from June to the end of November.