Tropical Storm Melissa is showing signs of reorganising as it continues to produce torrential rain across parts of the Caribbean.

The US National Hurricane Center has warned of life-threatening and potentially catastrophic flash flooding and landslides in southern Haiti and Jamaica through the weekend.

At 3pm GMT on Friday, Melissa was centred around 345 kilometres southeast of Kingston and 405 kilometres southwest of Port-au-Prince. Maximum sustained winds were recorded at 75 km/h.

Melissa is moving slowly to the east-southeast at 4 km/h. A gradual turn to the northeast and then north is expected later on Friday and into Saturday, before the storm shifts westward. On its current track the system is forecast to pass near or just south of Jamaica early next week.

Forecasters expect gradual strengthening today followed by rapid intensification over the weekend. Melissa is forecast to become a hurricane on Saturday and could reach major hurricane strength by Sunday.

A hurricane watch is in place for Jamaica and for the southwestern peninsula of Haiti. Both areas are also under tropical storm warnings.

The heaviest rainfall is expected in southern Haiti and eastern Jamaica where totals of 250 to 500 millimetres are likely, with locally higher amounts possible.

The National Hurricane Center says catastrophic flash flooding and landslides are likely in these regions. Further heavy rain is also expected across the southern Dominican Republic.

Minor coastal flooding may develop in Jamaica on Saturday as tropical-storm-force winds begin to affect the island. However, forecasters caution that the risk of a more significant storm surge early next week is uncertain due to Melissa’s slow movement and shifting structure.

Swells from the storm are already affecting parts of Hispaniola, Jamaica, and eastern Cuba.

Residents in the region are being urged to follow updates from local authorities.