This happened to me last night. Thought the weather had eased up for the day so I thought I'd go for a quick pootle. Road bike, no guards, biblongs and windproof gillet/jersey. Didn't really take notice of the clouds I was riding into
10 miles in, started to spit. Hmmm, don't mind a bit of drizzle..
Suddenly and without warning the heavens opened up to what I can only describe as a cow pissing on a flat rock!. I turned round and plowed through it the 10 miles back home. I looked as if I'd jumped in and out of a swimming pool. Shoes full of water etc.
I'll admit that mudguards would have helped but I wonder what waterproof jacket would have made a difference.
I think when it gets like that there isn't much you can do in regards to not getting wet. I think ill settle for a snorkel and HTFU.
Rob