+1 about the thunderstorms. No one will expect you to risk your life in order to finish the ride.
If you can get fenders for your bike, I recommend them. I have SKS Raceblades which are easy to put on my road bike when I need them. They will help keep you dry.
Put a bit less air in your tires than usual for better grip in wet conditions. Be careful when riding over metal (like manhole covers) or painted lines on the road. Also be careful if there are any wet leaves on the ground.
The jacket (which looks very nice, btw) is rated "warmer" by TE. My Showers Pass jacket has the same rating. I recently wore it for a rainy ride with temps in the low 60s. I wore a thin long sleeved wool base layer and a sleeveless jersey, and I was too warm. I've also worn it on a totally overcast day with temps in the high 40s and was too warm with the same wool base layer and a long sleeved jersey. So for temps in the 50s I would recommend one layer under your jacket. I'd probably go with a short sleeved jersey and arm warmers.
Sunglasses with clear or yellow lenses will help keep the rain out of your eyes. So will a helmet visor or cycling cap with a brim.
Good luck!!
- Gray 2010 carbon WSD road bike, Rivet Independence saddle
- Red hardtail 26" aluminum mountain bike, Bontrager Evoke WSD saddle
- Royal blue 2018 aluminum gravel bike, Rivet Pearl saddle
Gone but not forgotten:
- Silver 2003 aluminum road bike
- Two awesome worn out Juliana saddles