This is the standard setup for a lot of radios, ...
That may be true, but I regard it as less-than-optimal. The ICOM M402 that I'd been considering (for so long it's now out-of-production) didn't work that way, nor, near as I can tell, do the other ICOMs. The user's manual for the Standard Horizon Explorer GX 1600 says that radio doesn't work that way, either. Each of those, when you've got weather alert enabled,
always watches the weather channel. Somebody on another sailing forum has an older SH radio, and his doesn't require that it be scanning for the weather alert to work, either. So I'm really hoping the GX1500S user's manual is wrong.
The problem with having it work the way the user's manual for the GX1500S suggests, and the way you say your Raymarine works, is that if you're stopped on a channel, perhaps holding a conversation, and there's a weather alert, you'll miss it.
Thanks for the follow-up, Bill.
Jim