Large, silent green light moved very slowly NW towards Navy Base - abruptly changed course to SW and went supersonic (again, silent)

I was riding a scooter back towards my hotel, after having dinner at the Hard Rock restaurant in Key West Florida. I was slowing down to approach a stop sign at the end of Caroline Street, at Whitehall Street. I did not have anything to drink that evening. Cloud cover was low over the entire island. I noticed a large, green light just above the cloud cover, moving very slowly in a North-West direction, towards the Navy Base on Key West. When the light got fairly close to the Navy Base, it abruptly changed course in a South-West direction and sped up to a near-subsonic speed, quickly disappearing over the horizon (behind trees and buildings). Immediately after it disappeared, at least 6 other people on the sidewalk along Caroline Street started exclaiming about the light and it's strange behavior, along with me. We all wondered about it for a while, then continued on our separate ways. During the entire experience, the UFO made absolutely no sounds - the abrupt change of course and speed did not appear to have any affect on the object.