I haven't been stopped by any storm but I have a sheltered urban ride...there aren't any open areas where I'm exposed to risk of lightning strike or being blown off a bridge. Mind you, if the sky turns green I may run for cover.

Brakes are less effective when wet, but still should be adequate if they're properly tuned. Go a bit slower and ride more defensively. Don't challenge for right of way...they may not even see you...hang back at any intersection and go when it's clear. Don't worry about getting wet...it will happen. Once you're soaked, you can't get wetter, so relax. Ride with fenders...they may not keep you dry but they keep you relatively clean.