I live in So. Cal. , do a fair amount of 1 to 3 day Tuna trips out of the San Diego area and am willing to help out where ever I can. I do not know if you are referring to surf or charter fishing. I do not fish the surf but from what I understand So. Cal. surf fishery is not real exciting. But mabe more is happening then I realize, consequently I have attached 3 links below that should have resources for anything you need to know about the So Cal surf.
http://www.scsurffishing.com/
http://www.insidesportfishing.com/html/fishing_the_socal_surf.html
http://socalangling.tripod.com/
Now charter fishing is another story. It is unfortunate as to the time you will be here as from Sept. through May is the off season for the 1 to 3 day boats as far as the Albacore and Yellow Fin are concerned. You would have to go on at least a 5 day'er to get into the Yellow Fin but they are pricey (around $1800) . There are rare 1 to 3 day trips out of San Diego that go down in to Mexican waters and bottom fish for Rock fish and Yellow Tails.
My suggestion is to hit the All Coast Fishing Link below which has all the landing reports in the San Diego Bay area and check the fish counts of all the boats that go out. That will give you up to date firsh hand information on exactly what is happening. Here is how to do that.
Go to this link:
http://www.sport-fish-info.com/
Hit the FISHING REPORTS TAB
Scroll all the way to the bottom . The bottom 4: Seaforth Landing, H & M landing , Fishermans Landing and Point Loma Landing are all San Diego area Landings. They give the daily fish counts for all boats that go out and the duration of the trip. Start keeping track of whats happening a couple of weeks before you hit San Diego and you will be well informed on whats hot and whats not.
Like I said, if you need any more information on boat selection, techinques, active fisheries in Jan, anyting at all just fire away.
Walt