Yes, starting this morning we're seeing intermittent 502, 503 and 404 errors. Still looking into it, but making the same requests minutes later sometimes works.

I'm still working through transitioning to WeatherKit, but besides this change to when weather alerts are available, I've definitely experienced the regular 401 responses and the lack of summaries on weather alerts (there is no "messages" variable present in weather alerts like the REST docs show). I've had great results getting help from Apple by using a technical support incident (TSI). Support will try to help resolve the problem, otherwise they may reach out to a responsible engineer and verify if it's a known issue that's being worked on. I'm still rewriting my code and testing with Weatherkit, but if I'm still seeing these types of problems when I'm done that's what I'll try.

I've noticed this too. The precursor Dark Sky API returned weather alerts once they were issued, but Weatherkit isn't returning them until after the event onset time. Was this an intentional change?