MIAMI (AFP) - Tropical Storm Irma formed in the eastern Atlantic on Wednesday (Aug 30) and is forecast to gain hurricane strength as it heads towards the Caribbean, US weather monitors said.

Irma is currently some 770km west of Cape Verde, the Miami-based National Hurricane Centre said in its 2100 GMT bulletin (5am on Thursday, Singapore time).

It has maximum sustained winds of 95kmh and is moving west at a speed of 24kmh.

Irma comes in the wake of Harvey, which has pummelled Texas and Louisiana with soaking rains for days, unleashing deadly floods and leaving thousands of homes under water.

The storm is currently far from land, but heading straight towards the southern Caribbean, to the area between the US island territory of Puerto Rico and South America's northern coastline.

"Some strengthening is forecast during the next 48 hours and Irma is expected to become a hurricane Thursday or Friday," the NHC said.

Irma is forecast to reach the Lesser Antilles islands in the Caribbean in the middle of next week.