Tropical Storm Fiona could deliver a devastating 400mm of rain to some Caribbean islands.

Tropical Storm Fiona continues to move toward the Caribbean as more tropical storm watches are issued. The storm currently has estimated maximum sustained winds of 50mph, moving west at 15mph.

The rains from the tropical storm are forecast to start affecting the northern Leeward Islands, including the U.S. and British Virgin Islands Friday afternoon and evening.

Over the weekend Fiona will be around Puerto Rico and Hispaniola, which could receive up to 250mm of rain throughout the weekend. Flash flooding and mudslides are possible, especially over higher terrains. High seas are also forecast for the eastern Caribbean as Fiona travels over the region.

More devastating impacts may be possible for the Dominican Republic early Monday, where there could be nearer to 400mm of rain.

Fiona's impacts will largely depend on how much the system strengthens. There is plenty of dry air that could get into the system and wind shear that will disrupt its thunderstorm activity and shift it from the centre.

Fiona is also expected to move near or even over land, which tends to weaken systems, as they prefer to feed off the warm waters.

However, Fiona's track, and subsequent strength, will highly depend on how strong the Bermuda High (an Atlantic semi-permanent high-pressure system that tends to steer tropical storms and hurricanes) gets, and if it will then steer away from too much land.

It is currently located over the central north Atlantic and it seems it will retract a bit east allowing the system to swing northward, missing the U.S. East coast.

Later down the line, the storm system could get caught up in the jet stream and end up affecting our weather in the British Isles as an extra-tropical storm, however Fiona's track can still shift plenty in the next few days.