Hurricane Melissa strengthened into a Category 4 storm on Sunday, unleashing torrential rain and threatening to bring catastrophic flooding to the northern Caribbean.

Tropical Storm Melissa continues to slowly move northwest with sustained winds near 70 mph -- just shy of becoming the fifth hurricane of this Atlantic season.

Tropical Storm Melissa is set to intensify this weekend, and Jamaica and other Caribbean islands are bracing for harsh weather, forecasters with the National Hurricane Center in Miami said Thursday morning.

Tropical Storm Melissa has formed in the Caribbean, making it the 13th named storm in the Atlantic this year, the Miami-based National Hurricane Center announced Tuesday morning. The NEXT Weather team at CBS Miami said no direct impacts are expected to South Florida at this time,

The southern peninsula of Haiti remains under a hurricane watch, and all of Jamaica is under a hurricane watch and a tropical storm warning. Both countries are forecast to see a tremendous amount of rain, enough to potentially spawn life-threatening mudslides and flash flooding in Haiti and the island of Hispaniola.