Meteorologists have been tracking the storm for the past week, with its chances of forming increasing gradually. Tropical Storm Sara is expected to form by Thursday morning, becoming a hurricane by Friday night and a major hurricane by Saturday night, AccuWeather said.

The National Hurricane Center is tracking Invest99L as it moves over the central Caribbean Sea and gives the tropical rainstorm a 90% chance of developing into a tropical depression in the next two days.

The National Hurricane Center began advisories Wednesday on a system it forecasts to become the season’s next tropical depression or storm. Long-range forecast models predict it will intensify into a hurricane and threaten Florida by the middle of next week.