What's your definition of long period, though?
True about the sand sources - the spots I am thinking about may not have a rivermouth right THERE but within a couple miles for sure.
12-18, emphasis on 15-18?
Swells over 18 seconds are very rare here. Once every three to five summers, some fetch will stall right along South Africa and we'll get a true Southern Hemi in far North Florida.
North Florida tends to have some deeper sections of sandbar out the back, and it can turn the walls into long tapered lines. The Sebastian Inlet area and the Treasure Coast, those will be hammering closeouts at the beachbreaks.
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At what point are we calling an inlet a submarine canyon? El Porto has a massive canyon. It's not always that hot. St. Andrews, New Smyrna, Duranbah, and South Stradbroke have inlets. The first two might be Florida slop. The second two are Australia and therefore we have to make a big deal about some head high waves there.
Canyons are cool and all but they don't block wind. Give me some refraction resulting in positive interference and make it not too crowded and we're good.