You see this flashing yellow X signal above your lane. What does it mean?

Lane use signals control the traffic flow on lanes whose direction may change during the day. A flashing yellow signal above your lane indicates that the lane is for left turns only. Use this lane with caution; vehicles traveling in the opposite direction may use the lane for left turns, too. [Lane Control Signals, Traffic Signals, Chapter VI: Traffic Signs, Signals and Markings, Official Hawaii Driver's Manual]