Jamaica braced Saturday for strong winds and heavy rain from Tropical Storm Ernesto, which could build into a hurricane as it brushes past the island, US forecasters said.

At 1500 GMT, Ernesto was about 590 miles (950 kilometers) east-southeast of Kingston, moving westward at 18 miles per hour with top winds blowing at 50 miles per hour, according to the Miami-based National Hurricane Center.

The latest forecast says the storm would pass just south of the island as a category one hurricane on Monday, though the NHC urged Jamaicans to monitor Ernesto's progress.

Jamaica has issued a tropical storm watch for the island, meaning tropical storm conditions are possible in the coastal area within the next 48 hours.

But forecasters warned the storm is also headed for Honduras, Guatemala, Belize, Mexico's Yucatan Peninsula and Cuba as a hurricane between Tuesday and Thursday.

Further east, Tropical Storm Florence had top winds of 45 miles per hour as it moved in a west-northwestward direction at 16 miles per hour. The sixth named storm of the Atlantic season was located about 415 miles west of the southernmost Cape Verde Islands and was not expected to reach hurricane status.