An American traveler moving between Gulf and Atlantic beaches notices the difference immediately in the sand and the water. Both follow from the Gulf being a semi-enclosed basin.
Limited fetch means smaller waves
Wave size depends on wind speed, how long it blows, and the distance of open water it blows across. That distance, the fetch, is bounded in the Gulf and effectively unlimited on the open Atlantic.
The Atlantic coast also receives long-period swell generated by distant storms far offshore, energy that has traveled thousands of miles. The Gulf has far less access to such swell.
The practical result is that Gulf beaches are commonly calmer on an ordinary day, though tropical systems within the basin can produce severe conditions rapidly.
The sand comes from different places
Much of the sand along parts of the northern Gulf is quartz carried down from inland highlands over long geological periods, weathered and sorted until it is unusually fine and pale.
Atlantic beaches vary enormously along their length, ranging from coarse glacial material in the northeast to shell-rich and quartz sands further south, giving very different textures.
Grain size then drives beach slope. Fine sand produces the wide, flat, shallow-gradient beaches characteristic of much of the Gulf shore.
Water temperature reflects a shallow enclosed basin
A partially enclosed body of water with broad shallow margins warms more readily in summer than an open coast exposed to deep offshore circulation.
Atlantic beach temperature is also strongly affected by wind direction, since offshore winds can drive warm surface water away and bring cooler water up from below within a day.
Tidal range differs substantially
Tidal range along much of the Gulf is modest and the pattern in places differs from the twice-daily cycle familiar on the Atlantic coast, because tides depend on basin geometry.
A small range means the beach looks similar all day, while larger Atlantic ranges expose and cover substantial areas of sand and flats between tides.
What this means for choosing a trip
Calm shallow water and fine sand suit small children and long walks. Consistent surf, dramatic tidal change and cooler swimming suit different visitors entirely.
Neither coast is uniformly one thing, and conditions on any given day depend on wind and weather, so posted beach conditions and lifeguard guidance remain the reference for the water itself.