I’ve done several rain races and after the first 5-10 minutes I seriously forgot it was raining. The only real thing you need to be mindful of is whether any of the corners are slick, like painted lines or new asphalt etc. The water only really matters in the turns and then usually only if the road is unusually smooth.
The one time I had a rough time was a super technical crit on a freshly asphalted street that was like an ice skating rink. I freaked a bit and got lapped within 15 minutes but their were guys who looked to me like they hardly backed off at all. Of course, other guys crashed 