Hi makesurf.
Umina in a SW'er can be pretty ugly if the tides are high. Gets very messy & bumpy indeed. Went there the last big SSW'er and didn't even bother rigging as it looked very uninviting and dangerous!
If it goes S then it would be good when mid-tide or heading to low. Watch out for the sand banks which are frequent, but sailing behind them can give you some good runs.
Wave height for Saturday is 3m+ so be careful if you go. I will be checking it for a potential Sunday sail but Saturday is out for me.
Plenty of kiters to keep you company as well, mostly good guys/girls, just stay upwind of them if you can.