Weather predictions nine days out are always a bit fragile but right now, the National Weather Service is predicting that for the days of the con, San Diego will be having highs around 75° and lows around 70°, whereas the AccuWeather (private) service is saying highs around 80° and lows around 70°. So if you plan on highs around 78° and lows around 70°, you should be real close.
Those are temps for the entire city. Down by the water where the convention is, we usually have temps that are 5° lower unless you're in the middle of a crowd (add 10°) or you foolishly venture into the videogame areas of the convention hall where much of you will melt, starting with your ears.
And for those of you who keep campaigning to move the convention to Las Vegas, it will be at least 106° there. Which is one of about nineteen reasons why I think such a move will never happen. Nor should it, Dear God.