[orbat]

You generally need line-of-sight for microwave links and the longest known link is something like 350km, and even using tropospheric scatter you can't go over ~500km, so you'd need multiple relay stations with microwaves.

Using a lower band and bouncing off the ionosphere gets you much further but only works if ionosphere weather is OK, and it'll have lower bandwidth (not necessarily a problem though), and encryption is a no-no for amateur radio in most countries

[Bluestein]

What would it be like - heaven forbid - to have weather-dependant transatlantic links?

(Decently fast, just ... periodically off ...)