I love Ritas rain announcement, it basically says that its going to hurt like hell.
I will ALWAYS remember a TTF fireworks meet 2005/6 in the morning, myself, Kaycee, Ant and Sammie - Nemesis front row in torrential rain. I couldnt even open my eyes it was that painful. But the ride was phenomenally fast, and so intense.
2005... will never forget that ride, I had a hat on that came down over my eyes and I couldn't get it back up... most disorientating, crazy ride ever!
If it's really torrential rain, some rides will close as per ride operator training, because of potential to over-speed through the slippery brakes (only very minutely), which can cause breakdowns! On a couple of occasions I closed Oblivion very temporarily when the rain was ridiculous.
So it's only truly heavy, torrential rain that will cause closures, and as soon as it calms down, they'll re-open.
It's rare, so don't worry about it!