I think you know the answer - if you need to ask, don't.
A 30 knot wind off St Catherines point can easily be very nasty - albeit it, I'd be happy enough I could keep us safe if I got caught out and the weather turned. It's certainly doable, but running solo in a "small" rib (no offence intended - my best days boating ever used to be on a 4 or 5m searider with a 50/60 - and I am likely to own one again) with a nasty swell and no shelters or harbours on the south side if you change your mind or have a mechanical issue.....it's a what, 70 mile round trip? No problem when it's calm, but could be lifeboat nasty round st catherines in the rough.
Nasher's point re. swell - yeah, good point, sometimes you go past/round prince at the needles and it all smooths out.
But even so, 30 knots of wind, esp since it's been windy for a few days, will whip up a goodun round st catherines I reckon. I'd stay at home.