Invests run from 90 to 99, followed by a letter: L for the Atlantic basin and E for those in the eastern Pacific. After 99, it starts over again and the next invest would be 90.

The disturbance had a 90 percent chance of cyclone formation through seven days as of Friday, the National Hurricane Center said.

A tropical wave has been designated as Invest 91L. It's likely to become a tropical depression by the weekend.