Got home a while ago after a 2hr drive through continuous heavy rain here in the bay area. Speeds ranged from near standstill to 70ish. Visibility ranged from decent to poor (couldn't see 3-4 carlengths ahead) . I drove with AP enabled as much as it would stay on. Except for a 10 minute period through driving rain when it disengaged and would not turn back on, it worked very well. During the period where Autosteer would not work, TACC still worked fine. There were two instances where the AP 'lost' the lane marker dots (the lanes themselves were barely visible in the nighttime rain) and wandered into the adjacent lane. I let it wander while keeping track of the next lane, before bringing it back into my lane. Acceleration and deceleration were not jerky. I kept the spacing in front at 4 throughout, which was plenty. Overall, my experience follows this article: Tesla Autopilot Performs Surprisingly Well in Heavy Rain