Depends on the radio spectrum. Long range equals HF.

Your project boils down to a microphone accessory box on a radio. A
box connecting baro, temp, wind, etc to an hf radio could provide
worldwide coverage, so long as sufficient data was piggy backed over
normal operations, else a radio powering itself up periodically to
perform weather duties might be an objectionable usurpation of a
skipper's radio minimise traffic and power option.

Tx ID, GPS location and a packet of met sent out to any smartened
receiver in range could be routed to a network auto calculated at each
router to send the local report data shoreward. Confirmation would be
needed to enable routing reports. An optimal network must survive noisy
reception and minimise jabber.

So, a cable connector to a radio, incorperating met and routing data
might even display the best concocted weather map from local data or
even a podcast.

So, you need some software?

It seems it might be easiest if it was an option on a gps involving
satellite feedback of routing confirmations sent from world met report
hq. Otherwise, met reports would need to reproduce for a fixed time
period, growing in volume without retransmit control. Routing
confirmations minimise traffic. (minimal msg "id # rx'd ok (favoured
route node #)")

So, GPS would become a promulgation arm of a word wide weather net fed
by locals on radio, retransmission controlled, reception confirmed by
gps data. Isn't there a system like that already, using weathership
bouyes powered by wave and solar generators? It seems there should be
some bandwidth available on gps transmissions.

As well, with a "Sinking!" button on board, redundant emergency service
becomes a doddle.

Then, there is the local radar map on cell phone crowd who would like
it. With gps phones sending small paints to the traffic radar computer,
like in the English Channel?

Terry K