Intellicast is a great site and the only one I use for weather- it's owned by WSI Corp; this company supplies the aviation world with up-to-the-minute weather for flight planning. Go to your local airport and you'll see their dishes mounted on just about every corporate and FBO hangar. Their radar is just about as good as it gets. A good site to add to your favorites.
Jim

How is a wave actually measured? Is it from bottom out to the top, or is it from horizon to top? Is a 6ft swell actually 12ft from bottom to top?

crest to tough
The site has descriptions. Read through it.
The measurements are average in a short period of time. If its 3' seas there is likely to be a 4' or 5' sneak in every now and then. But one 5' in the bunch doesn't make it 5' seas.

That is why some people describe them as 3s and 5s.

Nice link. How do I physically measure a wave? I mean if I want to say i was in 4-5's what would be needed for the OSO gods to believe me?. Should I just hang over the swim platform with a tape measure and have somebody take a pic? Or maybe rig up a floaty with a pole?? Or should I just assume that the waves crashing over my bow are 4ft tall

Thanks Jim