Lots of factors in play but Tropical Storm Sara is expected to form this week and could become a major hurricane threatening the US next week.

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.

In a worst-case scenario for the U.S., a major hurricane could hit Florida's Gulf coast, but forecasters say it would have to clear several hurdles.