It is believed that Bali has 2 seasons: dry and wet. Dry lasts approximately from April to October. At this time, there is almost no rain, the temperature is about 26-27 degrees, the ocean is cool, and in the evenings you sometimes want to wear hoodies, especially for bike rides. This is the perfect time to surf on the south coast, the spots work great, the waves come in nice and even.
Then October comes and the first rains begin. It is getting hotter outside, the air is more humid and slowly but surely the island turns into a huge oven) the current changes and the water in the ocean becomes very warm. But at the same time, the winds are also changing, which drive heaps of garbage from Java to the shores of the southern coast.
Already now in Kuta you can swim with plastic cups, bottles, soft toys and lonely shale. Further it will be worse. Every day the beaches are cleaned, but, as you understand, it is impossible to clean everything. Have to put up with what you have. Waves begin to come to the west coast and everything smoothly moves there.
As for the rain, it happens in every way. Sometimes it doesn't rain for a week, sometimes it rains all night and it's sunny during the day. May pour a week without stopping. Maybe a couple of drops during the day. It rains the most in winter and closer to the center of the island.
By the way, if you are going to Bali and you check the weather forecast and see rain every day, don't worry) The fact is that the weather station is high in the mountains and it really drips there every day. But more often than not, when rain is forecast, the coast is dry and sunny.