Rule of thumb in Mauritius, when it's raining everywhere, head north to the beaches of Grand Baie. Most of the time the weather is good there. Which was true for us, as we escaped the rains of Port Louis and our party ended up on the beach. Mont Choisy is an old favourite beach as it's clean, the water really nice to be in, and the beach buzzing with a nice mix of people.
Mont Choisy beach is one of the beaches you can just take your beach bag and go off to the beach, as there's always many vendors selling food, ice cream, drinks and "konfi" (fruit salad with chillies), so you can grab something on the go.
Mont Choisy beach has clean waters to swim in as it's not full of corals, and there's designated safe areas to swim in. I have never actually seen a lifeguard on any of the Mauritian beaches though. There's changing room facilities (it does stink though), and there's a clean water cold shower outside to rinse off.
There's activities that you can do on the beach including tube riding (you sit on an inflatable seat and a speedboat drags you around, while you hold onto dear life) or parasailing (You are attached to a parachute and a speedboat drags you around. It is pretty slow up there, but you can take a moment and relax and enjoy the view). Prices vary depending on whether the people think you're a local or a tourist. Tube riding shouldn't cost you more than 200 rupees. Parasailing costs upwards of 800 rupees. I'd choose tube riding over parasailing any day.
Mont Choisy Beach
Address: Coastal Road, Mont Choisy, Grand Baie, North Mauritius
How to get there: Public transport (bus) from Port Louis, or taxi, or tour bus
Entrance fee: Free, public beach