I have just been up there and ridden some of the course. Currently very dry, even dusty in places, there are a couple of puddles, but you can ride around them all. I was on Small Block 8 tyres and they were fine.
The forecast for tomorrow looks to be a bit wet. I don’t think there has ever been a proper wet race a Frith Hill before, so not really sure how it will hold up to lots of rain and riders. Generally it is a fairly hard surface that drains well, and no clay, so I think it will be okay. I would imagine a few more roots will appear and a few sections will get cut up. Personally I would stick with the Rocket Rons, as there will be lots of sections where speed is more important than grip.