1. I just checked the hourly weather forecast for the next 48 hours. Starting about 1:00pm on Sunday each hour shows a 30% chance of isolated thunderstorms. These are not as heavy as scattered.
2. I would not suggest a canopy, they are more a hindrance than a help and if the rain is heavy it comes sideways anyway.
3. What I do is have two ponchos. One is over the seat and the other is over me, with the back over the seat. Yes, my lower legs and feet will get wet, but last time I looked I do not melt away.