Tropical storm Richard has formed in the Caribbean, becoming the 17th named storm of the Atlantic hurricane season.

Richard's maximum sustained winds Thursday were near 65 km/h. Additional strengthening is forecast, and Richard could become a hurricane over the weekend.

The National Hurricane Center in Miami says the tropical storm could dump 10 to 20 centimetres of rain on Jamaica, with some isolated areas getting 30 centimetres. These rains could cause life-threatening flash floods and mud slides.

Richard is located about 350 kilometres south-southeast of Grand Cayman and is moving southeast at about nine km/h.