Welcome to the WeatherCat forum!
Sorry you are having upload troubles. I am uploading to all three of those services so we know this feature works. Hang in there..
One thing we have noticed about uploading to WU from WeatherCat is complicated WU account passwords don't seem to work. If yours is complex, try changing it to a short simple one and see if that gets you out of the gate with WU. However, as you are unable to upload to WeatherCloud and PWS, that might indicate something more complicated with the setup. I assume you can see all your WeatherCat data on your iMac?
If you have enabled Log FTP Operations in WeatherCat | Preferences | Misc2 then you can check the WeatherCat logs in the Console app in Utilities. Open the Console and expand ~/Library/Logs. Then scroll down to WeatherCat. You will see 8 logs, covering today and the previous 7 days. You should be able to scroll through and find our what is being recorded to the log when WC attempts to FTP to the three services you are trying to access.
If you haven't yet enabled Log FTP Operations, there won't be anything to see. Enable it, wait a while, and then go look for the FTP messages in the log. Edouard, who is way smarter than me (but only in certain things), will likely log in later today and have other things for you to check.
Let us know as you make progress.