Randy,
There are several ways, but probably the least expensive is to listen to the WX broadcasts by the Coast Guard and other entities on the HF/SSB frequencies. This means you must have a receiver on board capable of receiving those reports, and you must know the schedules and frequencies.
If your
boat is not already equipped with a
SSB radio, you can buy a relatively inexpensive receiver for under $100 which can do a pretty good job. They sell under various names (Degen, Tecsun, and others) and are mostly made in
China. You might do some
research online to find out which ones are the
current favorites.
Times and frequencies for USCG
offshore and high seas broadcasts can be found on their website. Also, the
commercial marine station WLO in
New Orleans broadcasts
weather on a number of their working frequencies. The ham WaterWay net provides
East Coast weather at 0745 EDT daily on 7268 LSB, and the MM Net on 14300 sometimes provides weather info.
Nearshore (under 25 miles or so), you can get WX via
VHF from a network of coast stations.
There's a wealth of weather info on the WWW, if you have a way to get it (e.g., via satphone to someone ashore with a good
Internet connection).
There are several satellite-based solutions to obtain WX also, but they aren't cheap!
Bill