I have a similar issue. With my OLD VHF radio (a Standard, circa 2007) I could toggle between channel 16 and the weather channel (channel 2) with the 16/+ button.
In USA mode on my new Furuno VHF radio, I can't even see a number listed for a weather channel unless I drill down in the menu and turn on "Weather mode."
This does allow me to hear a weather channel, but I'm unable to program the weather channel as a secondary channel to toggle back and forth between 16.
Any suggestions on how to do this?