All moorings are a first come first serve basis. They are suppose to kick everyone out at 9am and then resell the moorings but that never happens. You pretty much take your chances. You can however get a water taxi from just about anywhere around avalon. Cost is another factor at 4 per person each way.
Good luck. You can always set the pick at the quary just to the east of avalon in usually nice conditions.
There is almost NO chance that you could get a can on Labor Day weekend. As Bill points out, your only small chance is if you went out there now and got on a can. Contrary to what was said above, the policy is not to kick off everyone off at 9 AM (assuming you are will to pay for the next day as the "mooring day" for payment purposes expires at 9AM just like a hotel checkout). Rather the policy is that, once you are on a can, you continue to be first in line and will not be kicked off for a non-owner who shows up (the owner has to call by midnight the night before to give the Harbour Dept notice that they must have the mooring open by 9 AM - hence the 9AM kickoff). If the owner shows up, you will be kicked off but given first priority to move to another free can if one is available. Last priority is given to those who are waiting out front but not currently on a can.
There is no way to check availability as the Harbor Dept will generally not respond to phone or radio calls (other than to say "nothing's available") unless you are there on your boat at the harbor mouth. That's the only you will get an open can. There is no way to reserve or get real info as to what might be open other than being there in person.
The likely outcome if you went out today is that you'd get on a can inside. Then by Thursday or Friday, you would get moved around and by Saturday you'd likely be thrown out completely but there's a SMALL chance that you would keep getting moved but still end up with a can out in Hamilton or Descanso. The whole thing is a pain because you must be on your boat until 9 AM on the mooring every day so you can respond to the Harbor Dept's request that you move or vacate. If you went out on Thursday the chance of retaining a can would be zero imo.
Avalon will be doing it's RV park imitation this weekend.Talked to a friend in the Del Ray Yacht club earlier today and he told me that they have over 30 boats leaving today for the long weekend. Just incase you havn't read enough in the previous posts. Mark/Time Out ch 72
You might have a chance if you can get there early..contact the red Harbor patrol boat and get on their list to go inside asap...you will probably be put on an outside mooring for a day or two or you can choose to anchor west toward White's Landing where it is usually more calm than off the outside Descanso or Hamilton Beach moorings...Between 7 and 9 am, they come by and tell you if an inside mooring has opened up..Departing boaters must be off the moorings by 9 am...Weekends are tough but weekdays frequently have openings even on popular dates... Good luck