One rating for a day at the beach or a swim. GoDay scores every daylight hour on warmth, sunshine, water temperature and how calm the sea is, then finds the best 2 hours of each day.
Also on the page, but not in the score: tide (a model estimate).
A thunderstorm holds the score at 1, and one due within two hours at 4. Air under 14°C (57°F) holds it at 2, and under 18°C (64°F) at 4. Steady rain holds it at 3, light rain at 5, waves over 2.5 m (8 ft) at 4, and heat over 40°C (104°F) at 4.
Daylight counts too: at dusk the score is held at 4, and once it's dark at 2.
Air of 26 to 36°C (79 to 97°F), mostly sunny skies, a breeze under 20 km/h (12 mph), and water of 21°C (70°F) or warmer.
GoDay rates the swim from wave height: up to 1 m (3 ft) is calm, and past 2.5 m (8 ft) it's rated dangerous. It can't see rips, currents or stingers, so swim where there are lifeguards and follow their advice.
Yes. UV is on the conditions cards, and very high UV counts a little against the score. Wear sunscreen whatever the rating says.