There's been a lot written about this, and I'll post some links for you....
And while Sirius will provide you with good coverage, I'd not be too quick to dump your wefax unit (I love my Furuno
FAX-408, and my old Alden still works most of the time)......but, if you decide to get rid of it, let me know.....
Not knowing how you are equipped, but someone considering offshore
passages should (in my opinion) not rely on just one source of weather data/forecasts, and certainly not put their eggs in the Sirius basket alone.....(since their coverage is good, but not complete.....and the data/forecasts they provide are availble elsewhere, for FREE, and much more reliably...)
Here are some photos of my Nav Station, showing my WeFax set-up, etc... Nav Station
Here's a discussion of weather data and forecasts for offshore
Where Do You Get Weather Updates in Bahamas ?
Here's some discussion of Sirius coverage in the Caribbean, etc...
And, here's some detailed Sirius Satellite
I do hope this helps....