Here's a problem you might not have considered when thinking about autonomous vehicles: what happens when it rains?

Ross Gerber, co-founder of Gerber Kawasaki and a long-time Tesla Inc. (TSLA) investor, shared his latest experience with the company's Full Self-Driving system on Wednesday, and it wasn't particularly encouraging for anyone living somewhere with weather.

When Cameras Can't Tell Rain From Dirt

Gerber took his Cybertruck out for a test drive in the rain running FSD version 14.2.1.25. The system promptly threw up an "Autopilot Visibility Limited" warning on the screen, asking him to clear dirt or debris from the FSD camera.

"There is no dirt. It's just rain," Gerber explained on X, the social media platform. He continued: "Not sure of teslas plans if FSD doesn't work well in rain or direct sunlight…"

The investor encouraged other users to try the system in wet conditions themselves. It's worth noting that Gerber had previously praised the improvements Tesla made with the v14 update, so this isn't just reflexive criticism from a skeptic.

Meanwhile, Musk Talks Up Robotaxi Progress

The timing of Gerber's rain report is interesting because Tesla CEO Elon Musk recently claimed significant progress on autonomous driving. Musk shared that he was driven around Austin in a Tesla Robotaxi with no safety monitor in the vehicle while he sat in the passenger seat.

If true, that would represent a meaningful step toward Musk's stated goal of launching driverless operations in Austin by the end of the year. A Tesla Robotaxi has also been spotted testing autonomously in the city recently.

But here's the thing: if the cameras struggle to distinguish raindrops from debris, that's a pretty fundamental challenge for a system that relies entirely on camera-based vision. No lidar, no radar in the newer models, just cameras. And apparently cameras that get confused when water falls from the sky.

Price Action: According to market data, TSLA slid 0.11% to $485.03 during the after-hours trading session.