A VTS operator observes a vessel on the radar that is steering a course of 090°T at a speed of 10 knots. However, the vessel's ground track (Course Over Ground) displayed by the system is 105°T, and its Speed Over Ground is 11 knots. What navigational phenomenon best explains this difference?

1. Gyrocompass error on the vessel.
2. Poor holding ground in the area.
3. The effect of wind on the vessel's superstructure (leeway).
4. A strong current setting in a southeasterly direction.