Tropical Storm Melissa is forecast to become a major hurricane within days. Although the exact track is uncertain, some models bring it close to Florida’s east coast.

Tropical Storm Melissa's forecast is filled with uncertainty, prompting some dire worst-case scenarios for Caribbean islands.

Tropical Storm Melissa is barely moving through the Caribbean, and that’s exactly what makes it so dangerous. The longer it lingers, the more rain it dumps. Haiti, Jamaica and the Dominican Republic could face days of relentless downpours and mudslides.

Melissa is expected to significantly strengthen by late Friday and over the weekend, when the storm could become a hurricane as early as Saturday.

Best-case scenario: “The best-case scenario for Florida would be if Melissa moves over eastern Cuba or Hispaniola and then gets pulled out to sea. That would spare Florida from impacts, though it would likely bring life-threatening and possibly catastrophic flooding to parts of Hispaniola, eastern Cuba, and the Dominican Republic."

This map from the National Hurricane Center shows the likely path of Hurricane Humberto as it tears through the Atlantic. The hurricane "is drifting slowly in weak steering currents," the center said, though it added that Humberto is "gradually increasing speed while moving west-northward to northwestward".

First Karen and then Jerry, both short-lived tropical storms fizzled in cooler Atlantic waters. Here's what's being watched now.