Tropical Storm Melissa is drifting slowly west-northwest through the central Caribbean, bringing heavy rainfall and flooding risks to Haiti and Jamaica over the coming days, according to the US National Hurricane Center (NHC).

At 3pm Irish time (10am local) the storm’s centre was located 485km south-southwest of Port-au-Prince in Haiti and 525km southeast of Kingston in Jamaica.

Maximum sustained winds were recorded at 85km/h with higher gusts, and further strengthening is expected. Melissa could reach hurricane strength by Friday.

A Hurricane Watch is in effect for Haiti’s southwestern peninsula from the Dominican border to Port-au-Prince while a Tropical Storm Watch is in place for Jamaica.

Melissa is forecast to continue moving slowly northwest before turning north-northwest then westward again by the weekend. The storm is expected to approach Jamaica and southwestern Haiti later this week.

Rainfall totals of 125 to 250mm are forecast across southern Haiti, the southern Dominican Republic and eastern Jamaica with higher amounts possible in some areas. Flash flooding and landslides are expected, particularly in mountainous regions.

The NHC also warned that swells generated by Melissa will affect Hispaniola, Jamaica and eastern Cuba over the next few days, creating hazardous surf and rip current conditions.

The minimum central pressure is estimated at 1000mb.